Accepted Manuscript Differential metabolic and endocrine adaptations in llamas, sheep and goats fed high and low protein grass-based diets A. Kiani, L. Alsted, M.O. Nielsen PII:
S0739-7240(15)00028-4
DOI:
10.1016/j.domaniend.2015.03.006
Reference:
DAE 6129
To appear in:
Domestic Animal Endocrinology
Received Date: 31 December 2014 Revised Date:
11 March 2015
Accepted Date: 14 March 2015
Please cite this article as: Kiani A, Alsted L, Nielsen MO, Differential metabolic and endocrine adaptations in llamas, sheep and goats fed high and low protein grass-based diets, Domestic Animal Endocrinology (2015), doi: 10.1016/j.domaniend.2015.03.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Differential metabolic and endocrine adaptations in llamas, sheep and goats fed high and
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low protein grass-based diets
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A. Kiani1 , L. Alsted2, and M. O. Nielsen2,*
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Khoramabad, Iran
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Sciences, University of Copenhagen, DK-1870 Frederiksberg C, Copenhagen, Denmark
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Animal Science Group, Faculty of Agricultural Sciences, Lorestan University, P. O. Box 465,
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Department of Veterinary Clinical and Animal Sciences, Faculty of Health and Medical
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Health and Medical Sciences, University of Copenhagen, DK-1870 Frederiksberg C,
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Copenhagen, Denmark. Tel: +45 35330365; Fax: +45 35333020.
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E-mail address: [email protected] (M.O. Nielsen).
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Corresponding author. Department of Veterinary Clinical and Animal Sciences, Faculty of
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Abstract This study aimed to elucidate whether distinct endocrine and metabolic adaptations provide llamas superior ability to adapt to low protein content grass-based diets as compared to the true
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ruminants. Eighteen adult, non-pregnant females (6 llamas, 6 goats and 6 sheep) were fed either
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green grass hay with (HP) or grass seed straw (LP) in a cross-over design experiment over two
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periods of 21 d. Blood samples were taken on day 21 in each period at -30, 60, 150 and 240 min
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after feeding the morning meal and analysed for plasma contents of glucose, triglyceride, non-
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esterified fatty acids, β-hydroxy butyrate (BOHB), urea, creatinine, insulin and leptin. Results
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showed that llamas versus sheep and goats had higher plasma concentrations of glucose (7.1 vs.
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3.5and 3.6 ±0.18 mmol/L), creatinine (209 vs. 110 and 103 ±10 µmol/L) and urea (6.7 vs. 5.6 and
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4.9 ±0.5mmol/L) but lower leptin (0.33 vs. 1.49 and 1.05 ±0.1 ng/ml) and BOHB (0.05 vs. 0.26
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and 0.12 ±0.02 mmol/L), respectively. BOHB in llamas was extremely low for a ruminating
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animal. Llamas showed hyperglycemia co-existed with hyperinsulinemia (in general on the HP
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diet; postprandially on the LP diet). Llamas were clearly hypercreatinaemic compared to the true
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ruminants, which became further exacerbated on the LP diet, where they also sustained plasma
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urea at markedly higher concentrations. However, llamas had markedly lower leptin
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concentrations than the true ruminants. In conclusion, llamas appear to have an intrinsic insulin
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resistant phenotype. Augmentation of creatinine and sustenance of elevated plasma urea
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concentrations in llamas when fed the LP diet must reflect distinct metabolic adaptations of
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intermediary protein/nitrogen metabolism, not observed in the true ruminants. These features can
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contribute to explain lower metabolic rates in llamas compared to the true ruminants, which must
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improve chances of survival on low protein content diets.
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Keywords: Hyperglycaemia; Insulin resistance; Creatinine; Urea; β-hydroxy butyrate
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1. Introduction Llamas (Lama-glama) are herbivorous ruminating animals with an expanded foregut and substantial microbial fermentation like other ruminant animals and with similar end-products of
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fermentation [1]. Despite the similarities with ruminants, the digestive tract in llamas differs
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from that of true ruminants anatomically with less complete separation of individual segments of
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the expanded foregut, and there are functional differences as well [1,2]. Llamas have been shown
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to have higher liquid passage rate but lower passage rate of solid material [3]. We [4]and others
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[5] have previously shown that llamas in addition have lower energy expenditure than ruminants.
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Furthermore, llamas have shown a superior ability to reduce energy requirements for
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maintenance on low protein content, grass-based diets compared to true ruminants [4].
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The functional differences between ruminants and llamas have allegedly provided llamas with a
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superior ability to digest and survive on diets with poor digestibility and low protein contents.
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It is reasonable to believe that this apparent superiority of llamas to small ruminants to survive
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on poor quality diets must be based on other evolutionary traits not only in the function of the
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digestive tract, but also in their intermediary metabolism. Llamas have been reported to have a
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greater protein requirement per unit of energy compared to other ruminants [6], although we
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have shown that they are capable of compensating for inadequate dietary nitrogen supply by
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reducing urinary nitrogen excretion [4]. A few studies have previously looked into metabolic
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characteristics of llamas compared to other true ruminants showing that camelids had high
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concentrations of blood glucose [7]. It has also been suggested that llamas may be able to recycle
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urea (i.e., transferring urea from blood to the digestive tract via saliva) more efficiently
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presumably due to a lower rate of kidney urea excretion and/or greater urease activity compared
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to the ruminants[8].The objective of this study was to test the hypothesis that distinct endocrine
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and metabolic adaptations in llamas have provided them superior ability as compared to the true
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ruminants to adapt to low protein content diets. To test this hypothesis, a comparative cross-over
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experiment was conducted, where metabolic and endocrine profiles were studied in llamas, sheep
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and goats when fed either artificially dried grass hay with 14.8% crude protein (HP) or grass
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seed straw with 6.2% crude protein (LP).
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2. Materials and Methods
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2.1. Experimental animals
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The experiment was conducted at the experimental facility for large animals, Rørrendegård,
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Faculty of Health and Medical Sciences, University of Copenhagen, HoejeTaastrup, Denmark.
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All experimental procedures were approved by the National Committee on Animal
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Experimentation, Denmark. Details regarding the experimental design, feeding, feed analyses,
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nutrient intakes and digestibilities, as well as quantitative data of energy and protein metabolism
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have previously been published by Nielsen et al [4]. Briefly, 18 mature and non-pregnant
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animals including 6 llamas, 6 Danish Landrace goats and 6 Shropshire sheep were used in a
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cross over design experiment. Llamas, sheep, and goats had135 ± 20, 75 ± 6 and 45 ± 5 kg live
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weight (mean ± SD) respectively. Prior to the onset of the experiment, all animals were given an
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anthelmintic treatment (Ivomec® Vet. Injektion (Merial, Skovlunde, Denmark). The experiment
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consisted of two consecutive periods. Each period lasted for 21 d; animals were fed to adlibtum
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to obtain 10% residuals. The daily ration was divided into two equally sized meals given at 07:30
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and 15:30 h. During each period, half of the animals within each species were fed either
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artificiallydried green grass hay with 14.8% crude protein (HP) and the other half were fed grass
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seed straw with 6.5% crude protein content (LP). Daily dry matter, crude protein, and energy
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intakes of llamas, sheep, and goats on both HP and LP diets is shown in Table 1.
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2.2. Blood sampling and blood analysis Blood samples were collected on day 21 in each experimental period at -30, 60, 150 and 240
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min related to the morning feeding time. The day before blood samplings, one jugular vein was
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catheterized under local anesthesia (Lidokain, AstraZeneca, Albertslund, Denmark) with a
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temporary catheter (Portextranslurent PVC, 0.63 ID, 1.40 OD, Smiths SIMS Portex limited,
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UK). Catheters were flushed with heparinized saline (100 IU/mL) after each blood sampling.
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Volume of each blood sample was about 10 mL and the first mL of collected blood was always
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discarded. Blood tubes were centrifuged at 2100 × g at 4°C for 15 min not later than 20 min after
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the blood was sampled. Plasma samples were subsequently transferred to cryotubes and stored at
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-20 °C pending analyses. The analysis plasma glucose, urea, creatinine, β-hydroxy-butyrate
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(BOHB), Non-esterified fatty acids (NEFA), and triglycerides (TG) were performed by using an
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autoanalyzer, ADVIA 1650® Chemistry System (Bayer Corporation, Tarrytown, NY 10592,
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USA) at the Faculty of Science and Technology, Aarhus University, Denmark. All blood
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samples were analyzed in duplicate. Blood plasma glucose and creatinine concentrations were
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determined according to standard procedures (Siemens Diagnostics® Clinical Methods for
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ADVIA 1650).NEFA were determined using the Wako enzymatic method (NEFA, ACS-ACOD
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assay method, Wako Chemicals, Richmond, USA). BOHB was determined by a
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spectrophotometric method [9]. The production of NADH was measured as an increase in the
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absorbance at 340 nm in the presence of β-hydroxybutyrate dehydrogenase in a slightly alkaline
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pH. Blank samples were included and oxamic acid was included in the media to inhibit lactate
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dehydrogenase. Leptin analyses were performed at the University of Western Australia, Perth, by
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a species-specific RIA using ovine leptin raised against bovine leptin[10]. The inter- and intra-
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assay coefficient of variations (CVs) for the leptin assay were below 5 and 10%, respectively.
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Insulin was analyzed with commercially available kits from Mercodia (Mercodia AB
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Sylvenniusgatan 8A, SE-754 50 Uppsala, Sweden). Ovine insulin ELISA was used for the sheep
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and the goats, while bovine insulin ELISA was used for the llamas. Samples for a given species
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were analyzed with one of the kits and no comparisons were made between the ovine and the
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bovine kit. The intra- and inter assay CVs for the specific type of kit were less than 7.5% for
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both the insulin kits.
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2.3. Statistical analysis
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The data were statistically analysed using SAS/STAT® software, version 9.2 of the SAS
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system for windows, copyright© 2008 SAS Institute Inc., Cary, NC, USA [11]. Normality of
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residuals was tested using Shapiro-Wilk test, and homogeneity of variance was evaluated by
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visual inspection of residuals plots. Data were analysed as a cross-over design with two diets (D:
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HP diet or LP diet) and three species (S: llama, sheep, and goat) studied at four different time
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points (TIME) of blood sampling (TIME: -30, 60, 150 and 240 min) and allocated to treatments
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in two different sequences (SEQ: HP followed by LP or LP followed by HP). The MIXED
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procedure was used for statistical analysis, where the main effects of D, S, SEQ, TIME were
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included as fixed effects and ANIMAL as a random effect. The interactions of the parameters
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were also included in the model, limited to 2-way interactions at most, but non-significant effects
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across all variables were excluded. Results are presented as least square means (LSM). Paired t-
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test (PDIFF option of MIXED) was used to examine simple treatment effects when interactions
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existed. Comparisons with P< 0.01 are declared highly significant, P< 0.05 significant and P >
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0.05 are considered as non-significant.
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3. Results Results for dietary intakes, nitrogen and energy digestibilities values as well as water balance and enteric methane emission have been reported previously [4].
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3.1. Plasma Glucose and Insulin
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Remarkably high plasma glucose values were observed in llamas, approximately twice as
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high as the concentrations observed in sheep and goats (Fig. 1). Plasma glucose concentration
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was not significantly different in sheep and in goats. The plasma concentration of glucose did not
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vary notably in relation to time after feeding in any of the three species.
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On the HP diet, llamas had the highest plasma concentrations of insulin followed by goats and sheep had the lowest insulin concentrations (Fig. 1). There were no differences in plasma
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insulin concentrations among the three species when they were fed the LP diet. Both llamas and
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goats but not sheep had lower insulin concentration on the LP compared to the HP diet.
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3.2. Plasma Leptin and Triglycerides
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Plasma leptin concentrations (ng/mL) in llamas were only about one fifth and one third, respectively, of those observed in sheep and goats (Fig. 2). Leptin concentration decreased
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significantly in sheep when shifted from the HP to the LP diet.
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Triglycerides concentrations in plasma (mmol/L) were generally of similar magnitude in
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llamas, sheep and goats and unaffected by the diet fed (Fig. 2). On the HP diet, concentrations of
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TG decreased significantly 4 h after feeding in sheep and goats, but increased to significantly
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higher concentrations in llamas than sheep and goats at this time point. No significant
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postprandial changes in TG concentrations were observed on the LP diet.
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3.3. Plasma NEFA and BOHB No species differences for NEFA concentration were observed when the HP diet was fed
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(Fig 3). NEFA concentrations were increased in all three species on the LP compared to HP diet,
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but in sheep NEFA concentrations increased at 60 and 150 min after feeding and to significantly
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higher concentrations than in llamas and goats. This postprandial NEFA increase was not
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observed in the llamas and goats.
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Sheep had almost twice as high plasma concentrations of BOHB (Fig. 3) than goats and
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approximately 15 times higher BOHB concentrations than llamas when fed the HP diet. Plasma
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concentration of BOHB decreased significantly in sheep, remained unaltered in goats, and
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increased in llamas when they were shifted from the HP to the LP diet.
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3.4. Plasma Urea and Creatinine
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plasma concentrations were decreased by more than 50% on the LP compared to the HP diet in
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sheep and goats, where llamas had a much smaller reduction in plasma urea on the LP diet. Thus,
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on the LP diet llamas had almost twice as high plasma urea concentrations compared to sheep
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and goats.
Llamas compared to sheep and goats had higher plasma concentrations of creatinine (Fig. 4).
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The creatinine plasma concentration was more than 50% higher than sheep and goats when fed
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the HP diet, and when llamas were fed the LP diet, their creatinine concentrations were further
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increased and reached concentrations more than twice as high as those observed in sheep and
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goats. Creatinineconcentrations in sheep and goats were comparable.
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4. Discussion
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4.1. Llamas have developed an insulin resistant phenotype
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reported previously in one other study [12]. These glucose concentrations found in llamas were
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almost twice as high as the values observed in the true ruminants, and substantially higher than
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other previously reported values for herbivore species (4.2 to 6.4 mmol/L) [13]. The
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hyperglycemia in llamas could hardly be ascribed to insufficiency of the pancreas to secrete
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insulin, since llamas compared to sheep and goats were also clearly hyperinsulinemic.
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Furthermore, the depression in pre-prandial insulin concentrations, when the LP rather than HP
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diet was fed, was much more pronounced in llamas than in sheep and goats, and only in the
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llamas was a postprandial increase in insulin observed on the LP diet. This clearly suggests that
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llamas have an intrinsic insulin resistant phenotype, which becomes clearly manifested under
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well-fed conditions.
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Llamas had very high plasma glucose concentrations (7.2 mmol/L or 130 mg/dL), as also
In diabetic humans, insulin resistance has often been associated with obesity and
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hyperleptinemia. The insulin resistance observed in llamas in this study was, however, not
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related to hyperleptinemia in any way, since llamas had extremely low concentrations of leptin
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when fed both the HP and LP diet compared to the true ruminant. It is well-known that plasma
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concentrations of leptin correlate positively with the degree of fatness in ruminant animals [14].
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Hence, the very low plasma concentrations of leptin in llamas agree well with very low fat
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contents in their body of around 3.5% of body weight [15] as compared to fat contents in a sheep
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carcass of about 25% [16].
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We previously reported that metabolic adaptations during evolution have enabled llamas to lower their energy expenditure and maintenance requirement compared to sheep and goats [4].
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This appears to be at least partly a consequence of the development of an intrinsic insulin
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resistant phenotype, which expectedly would be associated with lowered uptake and turnover of
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glucose in peripheral tissues, including the adipose tissue. It is possible that other metabolic
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adaptations contribute to the hyperglycemia observed in the llamas, such as increased rates of
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endogenous glucose production in gluconeogenetic pathways. Levels of PEPCK, a key enzyme
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in hepatic gluconeogenesis, have been reported to be 12 times higher in camel hump than in
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sheep tail [17]. If this also applies to the liver, it could obviously be associated with higher
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gluconeogenetic activity, but such studies have never been made in camelid species.
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4.2. Llamas have distinct adaptations in their intermediary nitrogen metabolism and excretion
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The present study demonstrated that when the LP diet with a low crude protein content (62
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g/kg DM) as compared to 148 g/kg DM in the HP diet was fed, plasma urea concentrations were
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decreased by more than 50% in the true ruminants as expected, whereas only a modest
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depression in urea concentrations was observed in llamas. In ruminating animals, urea is
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recycled to the foregut via saliva, and the excretion of urea into saliva is driven by a
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concentration gradient created by the urea concentration in plasma [18]. Our findings thus
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support the theory that llamas have greater ability, compared to the true ruminants, to recycle
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urea to the foregut when fed low protein diet, but not high protein containing diets due to their
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ability to sustain higher plasma urea concentration. On low protein diets, recycled urea can be an
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important source of nitrogen to sustain microbial fermentation and hence ensure efficient
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digestion and utilization of low protein content feeds [19].
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Despite higher plasma urea concentrations on the LP diet, llamas excreted similar daily
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quantity of nitrogen on a g per metabolic body weight bases (0.14, 0.13 and 0.20 ± 0.03 for
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llamas, sheep, and goat respectively) and on ag per day bases(4.9, 3.0, and 5.6 ± 1.1 for llamas, 10
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sheep, and goat respectively)[4]. This could be ascribed to a decrease in urine volume, whereas
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the concentration of nitrogen in the llama urine was unaffected by the diet [4]. The llama kidney
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thus appeared to reduce urinary nitrogen excretion, when the low protein diet was fed, associated
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with changes in water loss, and independently of plasma urea concentrations. The role played by
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this adaptation of kidney function in regulation of urea recycling remains to be established.
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An intriguing finding was that llamas had markedly higher plasma concentrations also of
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creatinine irrespectively of the diet. Plasma creatinine concentrations were increased even further
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in llamas when fed the LP diet, which was not seen in the true ruminants. This dietary impact
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was unexpected, since serum creatinine stems from muscle tissues, where it is synthesized in
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proportion to creatine and hence muscle mass in the body [20]. Creatinine is excreted in urine by
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renal filtration at a fairly constant rate, and serum creatinine is therefore a commonly used
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marker in the calculation of renal glomerular filtration rate in the human clinic [21]. Creatinine is
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also excreted into urine by tubular secretion, which is impacted by filtration fraction, i.e. the
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proportion of the renal arterial flow entering the renal tubules [22]. This in turn implies that any
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adaptation in a given animal of renal perfusion and filtration fraction potentially may have an
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impact on plasma creatinine as well as urea concentrations, just as it was observed in the llamas
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when fed the LP diet. It is therefore tempting to speculate that llamas during evolution have
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developed distinct mechanisms enabling them to reduce renal perfusion and/or filtration fraction
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and hence urinary nitrogen excretion, particularly when fed low protein diets. Whether high
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plasma creatinine concentrations in llamas could serve as a kind of "supply line" for delivery of
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nitrogen for urea synthesis and recycling to the gastrointestinal tract is an intriguing question that
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needs further investigations.
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4.3. Origin of BOHB in llamas? Plasma BOHB concentrations (0.01 mM/L) in llamas were extremely low on the HP diet,
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and almost equivalent to what can be observed in monogastric animals without any significant
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hindgut fermentation [23]. It was surprising that foregut fermentation was not clearly reflected
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on plasma BOHB concentrations in the llamas, since the relative proportions of acetate,
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propionate and butyrate produced during foregut fermentation was comparable in camelids
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species [24] to that of true ruminants. In agreement with the results of the present study,
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Chandransa et al [25] also reported that concentration of plasma BOHB and acetoacetate in the
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camel fed ad libitum were 33 and 4 times lower than those of the sheep. Basically, plasma
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BOHB originates either from partial oxidation of butyrate in the ruminal epithelium or liver
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following absorption [26], or it is produced during hepatic ketogenesis following incomplete
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oxidation of NEFA.The extremely low concentrations of BOHB in the blood of llamas fed the
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HP diet suggest that butyrate may not be oxidized to BOHB to the same extent in foregut
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epithelium and liver in llamas as in the true ruminants. In accordance with this, the activity of β-
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hydroxybutyrate dehydrogenase (BOHB-deH2) in the rumen epithelium of the camel has been
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reported to be about 10% of the activity found in the sheep [25]. Emmanual[26] also showed that
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the camels' rumen epithelium and liver oxidized negligible quantities of butyrate incompletely
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into ketone bodies or completely into CO2, whereas the camel kidney in contrast to the true
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ruminant kidney oxidized ketone bodies to a large extent.
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BOHB did, however, increase in llamas when fed the LP diet and to concentrations almost
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similar to those found in goats. This suggests that llamas are capable of producing BOHB just as
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the true ruminants as a result of hepatic ketogenesis, during a feeding associated with increased
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plasma concentrations of NEFA due to mobilization of body fat. This process is likely to be
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efficiently suppressed during more favorable nutrition conditions in llamas due to higher plasma
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concentrations of glucose and insulin, which will suppress adipose lipolysis and associated
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hepatic ketogenesis[27] just as in the true ruminants, and due to the generally lower amounts of
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mobilizable body fat in llamas. Thus, BOHB concentrations in llamas appear to reflect hepatic
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ketogenesis and thus metabolic state of the animal, unlike the true ruminants, where BOHB is
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highly influenced by foregut fermentation.
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Conclusions
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concentrations are indicators of an insulin resistant phenotype. The high plasma concentration of
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glucose might partly explain why llamas have lower energy expenditure and fat deposition
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compared to the small ruminant. Ability to uphold high plasma urea concentrations and
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particularly plasma creatinine concentrations on low protein diets, whilst reducing urinary
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nitrogen excretion, must reflect additional distinct adaptations of intermediary nitrogen
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metabolism possible at the renal excretory concentration. This would presumably result in more
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efficient recycling of nitrogen to sustain foregut fermentation on such diets. Together, these
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features may have been essential to improve the chances of survival of llamas in the harsh
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environments.
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Acknowledgments
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The present project was funded by the Danish Research Council for Development Research.
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The authors wish to thank guest researcher Mr. Einstein Tejada, lab technicians Ruth Jensen and
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Vibeke G. Christensen, and animal care taker Dennis S. Jensen, and the farm staff for expert
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technical assistance.
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References [1] San Martin F, Bryant FC. Nutrition of domesticated South American llamas and alpacas. Small Rumint Res. 1989; 2:191-216. [2] Rubsamen K, von Engelhardt W. Morphological and functional peculiarities of the llama forestomach. Ann Rech Vet. 1979; 10:473-475. [3] Robinson TF, Sponheimer M, Roeder BL, Passey B, Cerling TE, Dearing MD, Ehleringer JR. Digestibility and nitrogen retention in llamas and goats fed alfalfa, C3 grass, and C4 grass hays. Small Rumin Res. 2006; 64:162-168. [4] Nielsen MO, Kiani A, Tejada E, Chwalibog A, Alstrup L. Energy metabolism and methane production in llamas, sheep and goats fed high- and low-quality grass-based diets. Arch Animal Nutr. 2014; 68:171-185. [5] Vernet J, Vermorel M, Jouany JP. Digestibility and energy utilisation of three diets by llamas and sheep. Ann Zootech. 1997; 46:127-137. [6] Van Saun RJ. Nutrient requirements of South American camelids: A factorial approach. Small Rumin Res. 2006; 61:165-186. [7] Chandrasena LG, Emmanuel B, Gilanpour H. A comparative study of glucose metabolism between the camel (Camelus dromedarius) and the sheep (Ovis aries). Comp Biochem Physiol A Physiol. 1979; 62:837-840. [8] Hinderer S, Engelhardt W. Urea metabolism in the llama. Comp BiochemPhysiol A Physiol. 1975; 52:619622. [9] Harano Y, Ohtsuki M, Ida M, Kojima H, Harada M, Okanishi T, Kashiwagi A, Ochi Y, Uno S, Shigeta Y. Direct automated assay method for serum or urine levels of ketone bodies. Clin Chim Acta. 1985; 151:177183. [10] Blache D, Celi P, Blackberrv MA, Dynes RA, Martin GB. Decrease in voluntary feed intake and pulsatile luteinizing hormone secretion after intracerebroventricular infusion of recombinant bovine leptin in mature male sheep. Reprod Fertil Dev. 2000; 12:373-381. [11] SAS. Users guide:statistic. SAS Institute, Cary NC, 2008. [12] Cebra CK. Disorders of carbohydrate or lipid metabolism in camelids. Vet Clin North Am Food Anim Pract. 2009; 25:339-352. [13] Kaneko J, Harvey JW, Bruss ML. Clinical Biochemistry of Domestic Animals. Academic Press, 1997. [14] Chilliard Y, Bonnet M, Delavaud C, Faulconnier Y, Leroux C, Djiane J, Bocquier F. Leptin in ruminants. Gene expression in adipose tissue and mammary gland, and regulation of plasma concentration. Domest Anim Endocrinol. 2001; 21:271-295. [15] Polidori P, Renieri C, Antonini M, Passamoniti P, Pucciarelli F. Meat fatty acid composition of llama (Lama glama) reared in the Andean highlands. Meat Sci. 2007; 75:356-358. [16] Mahgoub o, Lodge GA. A comparative study on growth, body composition and carcass tissue distribution in Omani sheep and goats. J Agr Sci. 1998; 131:329-339. [17] Al-Rehaimi AA, Al-Ali AK, Mutairy AR, Dissanayake AS. A comparative study of enzyme profile of camel (Camelus dromedarius) hump and sheep (Ovis aries) tail tissues. Comp Bioch Physiol B Comp Bioch. 1989; 93:857-858. [18] Sands JM, Layton HE. The physiology of urinary concentration: an update. Semin Nephrol. 2009; 29:178195. [19] Reynolds CK, Kristensen NB. Nitrogen recycling through the gut and the nitrogen economy of ruminants: An asynchronous symbiosis. J Anim Sci. 2008; 86:E293-E305. [20] Heymsfield SB, Arteaga C, McManus C, Smith J, Moffitt S. Measurement of muscle mass in humans: validity of the 24-hour urinary creatinine method. Am J Clin Nutr. 1983; 37:478-494. [21] Lin Y, Bansal N, Vittinghoff E, Go A, Hsu C. Determinants of the creatinine clearance to glomerular filtration rate ratio in patients with chronic kidney disease: a cross-sectional study. BMC Nephrol. 2013; 14:268. [22] Huang SH, Sharma AP, Yasin A, Lindsay RM, Clark WF, Filler G. Hyperfiltration Affects Accuracy of Creatinine eGFR Measurement. Clin J Am Soc Nephro. 2011; 6:274-280. [23] Bengtsson G, Gentz J, Hakkarainen J, Hellstrom R, Persson B. Plasma levels of FFA, glycerol, βhydroxybutyrate and blood glucose during the postnatal development of the pig. J Nutr. 1969; 97:311-315. [24] Liu Q, Dong CS, Li HQ, Yang WZ, Jiang JB, Gao WJ, Pei CX, Qiao JJ. Effects of feeding sorghum-sudan, alfalfa hay and fresh alfalfa with concentrate on intake, first compartment stomach characteristics, digestibility, nitrogen balance and energy metabolism in alpacas (Lama pacos) at low altitude. Livest Sci. 2009; 126:21-27.
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[25] Chandrasena LG, Emmanuel B, Hamar DW, Howard BR. A comparative study of ketone body metabolism between the camel (Camelus dromedarius) and the sheep (Ovis aries). Comp Biochem Physiol B Comp Biochem. 1979; 64:109-112. [26] Emmanuel B. Oxidation of butyrate to ketone bodies and CO2 in the rumen epithelium, liver, kidney, heart and lung of camel (Camelus dromedarius), sheep (Ovis aries) and goat (Carpa hircus). Comp Biochem Physiol B Comp Biochem. 1980; 65:699-704. [27] Berg JM, Tymoczko JL, Stryer L. Biochemistry. Liberary of Congress, 2006.
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Table 1 Daily dry matter, crude protein and energy intakes in llamas, sheep and goats fed either dried green grass hay with high protein (HP) content or grass seed straw with low protein (LP) content
Dry matter intake (g) 1736a 1406b 637d Crude protein intake (g)
a
257
Gross energy (MJ) 32.7a a
94
c
66
cde
26.5b 12.0d 18.3c b
c
c
884c d
61
622d
67
*** *** ***
de
9.2
*** *** ***
1.3
*** *** ***
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16.8c 11.8d c
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Digested energy (MJ) 20.8 16.0 7.5 7.3 6.0 2.6 1.1 *** *** ** Values are least squares means ± standard error of means (SEM); a,b,c Mean values within a row with different superscript letters were significantly different (P
S0739-7240(15)00028-4
DOI:
10.1016/j.domaniend.2015.03.006
Reference:
DAE 6129
To appear in:
Domestic Animal Endocrinology
Received Date: 31 December 2014 Revised Date:
11 March 2015
Accepted Date: 14 March 2015
Please cite this article as: Kiani A, Alsted L, Nielsen MO, Differential metabolic and endocrine adaptations in llamas, sheep and goats fed high and low protein grass-based diets, Domestic Animal Endocrinology (2015), doi: 10.1016/j.domaniend.2015.03.006. This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Differential metabolic and endocrine adaptations in llamas, sheep and goats fed high and
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low protein grass-based diets
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A. Kiani1 , L. Alsted2, and M. O. Nielsen2,*
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Khoramabad, Iran
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Sciences, University of Copenhagen, DK-1870 Frederiksberg C, Copenhagen, Denmark
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Animal Science Group, Faculty of Agricultural Sciences, Lorestan University, P. O. Box 465,
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Department of Veterinary Clinical and Animal Sciences, Faculty of Health and Medical
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Health and Medical Sciences, University of Copenhagen, DK-1870 Frederiksberg C,
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Copenhagen, Denmark. Tel: +45 35330365; Fax: +45 35333020.
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E-mail address: [email protected] (M.O. Nielsen).
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Corresponding author. Department of Veterinary Clinical and Animal Sciences, Faculty of
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Abstract This study aimed to elucidate whether distinct endocrine and metabolic adaptations provide llamas superior ability to adapt to low protein content grass-based diets as compared to the true
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ruminants. Eighteen adult, non-pregnant females (6 llamas, 6 goats and 6 sheep) were fed either
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green grass hay with (HP) or grass seed straw (LP) in a cross-over design experiment over two
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periods of 21 d. Blood samples were taken on day 21 in each period at -30, 60, 150 and 240 min
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after feeding the morning meal and analysed for plasma contents of glucose, triglyceride, non-
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esterified fatty acids, β-hydroxy butyrate (BOHB), urea, creatinine, insulin and leptin. Results
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showed that llamas versus sheep and goats had higher plasma concentrations of glucose (7.1 vs.
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3.5and 3.6 ±0.18 mmol/L), creatinine (209 vs. 110 and 103 ±10 µmol/L) and urea (6.7 vs. 5.6 and
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4.9 ±0.5mmol/L) but lower leptin (0.33 vs. 1.49 and 1.05 ±0.1 ng/ml) and BOHB (0.05 vs. 0.26
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and 0.12 ±0.02 mmol/L), respectively. BOHB in llamas was extremely low for a ruminating
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animal. Llamas showed hyperglycemia co-existed with hyperinsulinemia (in general on the HP
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diet; postprandially on the LP diet). Llamas were clearly hypercreatinaemic compared to the true
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ruminants, which became further exacerbated on the LP diet, where they also sustained plasma
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urea at markedly higher concentrations. However, llamas had markedly lower leptin
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concentrations than the true ruminants. In conclusion, llamas appear to have an intrinsic insulin
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resistant phenotype. Augmentation of creatinine and sustenance of elevated plasma urea
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concentrations in llamas when fed the LP diet must reflect distinct metabolic adaptations of
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intermediary protein/nitrogen metabolism, not observed in the true ruminants. These features can
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contribute to explain lower metabolic rates in llamas compared to the true ruminants, which must
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improve chances of survival on low protein content diets.
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Keywords: Hyperglycaemia; Insulin resistance; Creatinine; Urea; β-hydroxy butyrate
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1. Introduction Llamas (Lama-glama) are herbivorous ruminating animals with an expanded foregut and substantial microbial fermentation like other ruminant animals and with similar end-products of
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fermentation [1]. Despite the similarities with ruminants, the digestive tract in llamas differs
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from that of true ruminants anatomically with less complete separation of individual segments of
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the expanded foregut, and there are functional differences as well [1,2]. Llamas have been shown
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to have higher liquid passage rate but lower passage rate of solid material [3]. We [4]and others
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[5] have previously shown that llamas in addition have lower energy expenditure than ruminants.
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Furthermore, llamas have shown a superior ability to reduce energy requirements for
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maintenance on low protein content, grass-based diets compared to true ruminants [4].
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The functional differences between ruminants and llamas have allegedly provided llamas with a
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superior ability to digest and survive on diets with poor digestibility and low protein contents.
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It is reasonable to believe that this apparent superiority of llamas to small ruminants to survive
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on poor quality diets must be based on other evolutionary traits not only in the function of the
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digestive tract, but also in their intermediary metabolism. Llamas have been reported to have a
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greater protein requirement per unit of energy compared to other ruminants [6], although we
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have shown that they are capable of compensating for inadequate dietary nitrogen supply by
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reducing urinary nitrogen excretion [4]. A few studies have previously looked into metabolic
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characteristics of llamas compared to other true ruminants showing that camelids had high
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concentrations of blood glucose [7]. It has also been suggested that llamas may be able to recycle
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urea (i.e., transferring urea from blood to the digestive tract via saliva) more efficiently
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presumably due to a lower rate of kidney urea excretion and/or greater urease activity compared
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to the ruminants[8].The objective of this study was to test the hypothesis that distinct endocrine
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and metabolic adaptations in llamas have provided them superior ability as compared to the true
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ruminants to adapt to low protein content diets. To test this hypothesis, a comparative cross-over
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experiment was conducted, where metabolic and endocrine profiles were studied in llamas, sheep
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and goats when fed either artificially dried grass hay with 14.8% crude protein (HP) or grass
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seed straw with 6.2% crude protein (LP).
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2. Materials and Methods
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2.1. Experimental animals
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The experiment was conducted at the experimental facility for large animals, Rørrendegård,
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Faculty of Health and Medical Sciences, University of Copenhagen, HoejeTaastrup, Denmark.
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All experimental procedures were approved by the National Committee on Animal
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Experimentation, Denmark. Details regarding the experimental design, feeding, feed analyses,
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nutrient intakes and digestibilities, as well as quantitative data of energy and protein metabolism
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have previously been published by Nielsen et al [4]. Briefly, 18 mature and non-pregnant
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animals including 6 llamas, 6 Danish Landrace goats and 6 Shropshire sheep were used in a
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cross over design experiment. Llamas, sheep, and goats had135 ± 20, 75 ± 6 and 45 ± 5 kg live
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weight (mean ± SD) respectively. Prior to the onset of the experiment, all animals were given an
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anthelmintic treatment (Ivomec® Vet. Injektion (Merial, Skovlunde, Denmark). The experiment
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consisted of two consecutive periods. Each period lasted for 21 d; animals were fed to adlibtum
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to obtain 10% residuals. The daily ration was divided into two equally sized meals given at 07:30
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and 15:30 h. During each period, half of the animals within each species were fed either
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artificiallydried green grass hay with 14.8% crude protein (HP) and the other half were fed grass
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seed straw with 6.5% crude protein content (LP). Daily dry matter, crude protein, and energy
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intakes of llamas, sheep, and goats on both HP and LP diets is shown in Table 1.
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2.2. Blood sampling and blood analysis Blood samples were collected on day 21 in each experimental period at -30, 60, 150 and 240
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min related to the morning feeding time. The day before blood samplings, one jugular vein was
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catheterized under local anesthesia (Lidokain, AstraZeneca, Albertslund, Denmark) with a
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temporary catheter (Portextranslurent PVC, 0.63 ID, 1.40 OD, Smiths SIMS Portex limited,
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UK). Catheters were flushed with heparinized saline (100 IU/mL) after each blood sampling.
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Volume of each blood sample was about 10 mL and the first mL of collected blood was always
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discarded. Blood tubes were centrifuged at 2100 × g at 4°C for 15 min not later than 20 min after
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the blood was sampled. Plasma samples were subsequently transferred to cryotubes and stored at
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-20 °C pending analyses. The analysis plasma glucose, urea, creatinine, β-hydroxy-butyrate
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(BOHB), Non-esterified fatty acids (NEFA), and triglycerides (TG) were performed by using an
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autoanalyzer, ADVIA 1650® Chemistry System (Bayer Corporation, Tarrytown, NY 10592,
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USA) at the Faculty of Science and Technology, Aarhus University, Denmark. All blood
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samples were analyzed in duplicate. Blood plasma glucose and creatinine concentrations were
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determined according to standard procedures (Siemens Diagnostics® Clinical Methods for
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ADVIA 1650).NEFA were determined using the Wako enzymatic method (NEFA, ACS-ACOD
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assay method, Wako Chemicals, Richmond, USA). BOHB was determined by a
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spectrophotometric method [9]. The production of NADH was measured as an increase in the
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absorbance at 340 nm in the presence of β-hydroxybutyrate dehydrogenase in a slightly alkaline
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pH. Blank samples were included and oxamic acid was included in the media to inhibit lactate
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dehydrogenase. Leptin analyses were performed at the University of Western Australia, Perth, by
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a species-specific RIA using ovine leptin raised against bovine leptin[10]. The inter- and intra-
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assay coefficient of variations (CVs) for the leptin assay were below 5 and 10%, respectively.
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Insulin was analyzed with commercially available kits from Mercodia (Mercodia AB
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Sylvenniusgatan 8A, SE-754 50 Uppsala, Sweden). Ovine insulin ELISA was used for the sheep
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and the goats, while bovine insulin ELISA was used for the llamas. Samples for a given species
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were analyzed with one of the kits and no comparisons were made between the ovine and the
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bovine kit. The intra- and inter assay CVs for the specific type of kit were less than 7.5% for
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both the insulin kits.
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2.3. Statistical analysis
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The data were statistically analysed using SAS/STAT® software, version 9.2 of the SAS
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system for windows, copyright© 2008 SAS Institute Inc., Cary, NC, USA [11]. Normality of
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residuals was tested using Shapiro-Wilk test, and homogeneity of variance was evaluated by
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visual inspection of residuals plots. Data were analysed as a cross-over design with two diets (D:
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HP diet or LP diet) and three species (S: llama, sheep, and goat) studied at four different time
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points (TIME) of blood sampling (TIME: -30, 60, 150 and 240 min) and allocated to treatments
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in two different sequences (SEQ: HP followed by LP or LP followed by HP). The MIXED
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procedure was used for statistical analysis, where the main effects of D, S, SEQ, TIME were
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included as fixed effects and ANIMAL as a random effect. The interactions of the parameters
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were also included in the model, limited to 2-way interactions at most, but non-significant effects
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across all variables were excluded. Results are presented as least square means (LSM). Paired t-
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test (PDIFF option of MIXED) was used to examine simple treatment effects when interactions
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existed. Comparisons with P< 0.01 are declared highly significant, P< 0.05 significant and P >
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0.05 are considered as non-significant.
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3. Results Results for dietary intakes, nitrogen and energy digestibilities values as well as water balance and enteric methane emission have been reported previously [4].
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3.1. Plasma Glucose and Insulin
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Remarkably high plasma glucose values were observed in llamas, approximately twice as
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high as the concentrations observed in sheep and goats (Fig. 1). Plasma glucose concentration
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was not significantly different in sheep and in goats. The plasma concentration of glucose did not
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vary notably in relation to time after feeding in any of the three species.
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On the HP diet, llamas had the highest plasma concentrations of insulin followed by goats and sheep had the lowest insulin concentrations (Fig. 1). There were no differences in plasma
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insulin concentrations among the three species when they were fed the LP diet. Both llamas and
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goats but not sheep had lower insulin concentration on the LP compared to the HP diet.
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3.2. Plasma Leptin and Triglycerides
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Plasma leptin concentrations (ng/mL) in llamas were only about one fifth and one third, respectively, of those observed in sheep and goats (Fig. 2). Leptin concentration decreased
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significantly in sheep when shifted from the HP to the LP diet.
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Triglycerides concentrations in plasma (mmol/L) were generally of similar magnitude in
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llamas, sheep and goats and unaffected by the diet fed (Fig. 2). On the HP diet, concentrations of
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TG decreased significantly 4 h after feeding in sheep and goats, but increased to significantly
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higher concentrations in llamas than sheep and goats at this time point. No significant
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postprandial changes in TG concentrations were observed on the LP diet.
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3.3. Plasma NEFA and BOHB No species differences for NEFA concentration were observed when the HP diet was fed
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(Fig 3). NEFA concentrations were increased in all three species on the LP compared to HP diet,
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but in sheep NEFA concentrations increased at 60 and 150 min after feeding and to significantly
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higher concentrations than in llamas and goats. This postprandial NEFA increase was not
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observed in the llamas and goats.
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Sheep had almost twice as high plasma concentrations of BOHB (Fig. 3) than goats and
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approximately 15 times higher BOHB concentrations than llamas when fed the HP diet. Plasma
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concentration of BOHB decreased significantly in sheep, remained unaltered in goats, and
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increased in llamas when they were shifted from the HP to the LP diet.
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3.4. Plasma Urea and Creatinine
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plasma concentrations were decreased by more than 50% on the LP compared to the HP diet in
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sheep and goats, where llamas had a much smaller reduction in plasma urea on the LP diet. Thus,
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on the LP diet llamas had almost twice as high plasma urea concentrations compared to sheep
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and goats.
Llamas compared to sheep and goats had higher plasma concentrations of creatinine (Fig. 4).
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The creatinine plasma concentration was more than 50% higher than sheep and goats when fed
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the HP diet, and when llamas were fed the LP diet, their creatinine concentrations were further
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increased and reached concentrations more than twice as high as those observed in sheep and
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goats. Creatinineconcentrations in sheep and goats were comparable.
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4. Discussion
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4.1. Llamas have developed an insulin resistant phenotype
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reported previously in one other study [12]. These glucose concentrations found in llamas were
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almost twice as high as the values observed in the true ruminants, and substantially higher than
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other previously reported values for herbivore species (4.2 to 6.4 mmol/L) [13]. The
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hyperglycemia in llamas could hardly be ascribed to insufficiency of the pancreas to secrete
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insulin, since llamas compared to sheep and goats were also clearly hyperinsulinemic.
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Furthermore, the depression in pre-prandial insulin concentrations, when the LP rather than HP
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diet was fed, was much more pronounced in llamas than in sheep and goats, and only in the
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llamas was a postprandial increase in insulin observed on the LP diet. This clearly suggests that
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llamas have an intrinsic insulin resistant phenotype, which becomes clearly manifested under
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well-fed conditions.
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Llamas had very high plasma glucose concentrations (7.2 mmol/L or 130 mg/dL), as also
In diabetic humans, insulin resistance has often been associated with obesity and
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hyperleptinemia. The insulin resistance observed in llamas in this study was, however, not
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related to hyperleptinemia in any way, since llamas had extremely low concentrations of leptin
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when fed both the HP and LP diet compared to the true ruminant. It is well-known that plasma
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concentrations of leptin correlate positively with the degree of fatness in ruminant animals [14].
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Hence, the very low plasma concentrations of leptin in llamas agree well with very low fat
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contents in their body of around 3.5% of body weight [15] as compared to fat contents in a sheep
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carcass of about 25% [16].
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We previously reported that metabolic adaptations during evolution have enabled llamas to lower their energy expenditure and maintenance requirement compared to sheep and goats [4].
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This appears to be at least partly a consequence of the development of an intrinsic insulin
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resistant phenotype, which expectedly would be associated with lowered uptake and turnover of
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glucose in peripheral tissues, including the adipose tissue. It is possible that other metabolic
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adaptations contribute to the hyperglycemia observed in the llamas, such as increased rates of
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endogenous glucose production in gluconeogenetic pathways. Levels of PEPCK, a key enzyme
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in hepatic gluconeogenesis, have been reported to be 12 times higher in camel hump than in
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sheep tail [17]. If this also applies to the liver, it could obviously be associated with higher
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gluconeogenetic activity, but such studies have never been made in camelid species.
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4.2. Llamas have distinct adaptations in their intermediary nitrogen metabolism and excretion
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The present study demonstrated that when the LP diet with a low crude protein content (62
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g/kg DM) as compared to 148 g/kg DM in the HP diet was fed, plasma urea concentrations were
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decreased by more than 50% in the true ruminants as expected, whereas only a modest
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depression in urea concentrations was observed in llamas. In ruminating animals, urea is
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recycled to the foregut via saliva, and the excretion of urea into saliva is driven by a
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concentration gradient created by the urea concentration in plasma [18]. Our findings thus
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support the theory that llamas have greater ability, compared to the true ruminants, to recycle
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urea to the foregut when fed low protein diet, but not high protein containing diets due to their
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ability to sustain higher plasma urea concentration. On low protein diets, recycled urea can be an
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important source of nitrogen to sustain microbial fermentation and hence ensure efficient
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digestion and utilization of low protein content feeds [19].
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Despite higher plasma urea concentrations on the LP diet, llamas excreted similar daily
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quantity of nitrogen on a g per metabolic body weight bases (0.14, 0.13 and 0.20 ± 0.03 for
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llamas, sheep, and goat respectively) and on ag per day bases(4.9, 3.0, and 5.6 ± 1.1 for llamas, 10
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sheep, and goat respectively)[4]. This could be ascribed to a decrease in urine volume, whereas
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the concentration of nitrogen in the llama urine was unaffected by the diet [4]. The llama kidney
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thus appeared to reduce urinary nitrogen excretion, when the low protein diet was fed, associated
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with changes in water loss, and independently of plasma urea concentrations. The role played by
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this adaptation of kidney function in regulation of urea recycling remains to be established.
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An intriguing finding was that llamas had markedly higher plasma concentrations also of
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creatinine irrespectively of the diet. Plasma creatinine concentrations were increased even further
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in llamas when fed the LP diet, which was not seen in the true ruminants. This dietary impact
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was unexpected, since serum creatinine stems from muscle tissues, where it is synthesized in
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proportion to creatine and hence muscle mass in the body [20]. Creatinine is excreted in urine by
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renal filtration at a fairly constant rate, and serum creatinine is therefore a commonly used
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marker in the calculation of renal glomerular filtration rate in the human clinic [21]. Creatinine is
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also excreted into urine by tubular secretion, which is impacted by filtration fraction, i.e. the
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proportion of the renal arterial flow entering the renal tubules [22]. This in turn implies that any
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adaptation in a given animal of renal perfusion and filtration fraction potentially may have an
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impact on plasma creatinine as well as urea concentrations, just as it was observed in the llamas
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when fed the LP diet. It is therefore tempting to speculate that llamas during evolution have
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developed distinct mechanisms enabling them to reduce renal perfusion and/or filtration fraction
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and hence urinary nitrogen excretion, particularly when fed low protein diets. Whether high
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plasma creatinine concentrations in llamas could serve as a kind of "supply line" for delivery of
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nitrogen for urea synthesis and recycling to the gastrointestinal tract is an intriguing question that
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needs further investigations.
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4.3. Origin of BOHB in llamas? Plasma BOHB concentrations (0.01 mM/L) in llamas were extremely low on the HP diet,
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and almost equivalent to what can be observed in monogastric animals without any significant
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hindgut fermentation [23]. It was surprising that foregut fermentation was not clearly reflected
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on plasma BOHB concentrations in the llamas, since the relative proportions of acetate,
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propionate and butyrate produced during foregut fermentation was comparable in camelids
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species [24] to that of true ruminants. In agreement with the results of the present study,
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Chandransa et al [25] also reported that concentration of plasma BOHB and acetoacetate in the
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camel fed ad libitum were 33 and 4 times lower than those of the sheep. Basically, plasma
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BOHB originates either from partial oxidation of butyrate in the ruminal epithelium or liver
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following absorption [26], or it is produced during hepatic ketogenesis following incomplete
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oxidation of NEFA.The extremely low concentrations of BOHB in the blood of llamas fed the
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HP diet suggest that butyrate may not be oxidized to BOHB to the same extent in foregut
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epithelium and liver in llamas as in the true ruminants. In accordance with this, the activity of β-
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hydroxybutyrate dehydrogenase (BOHB-deH2) in the rumen epithelium of the camel has been
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reported to be about 10% of the activity found in the sheep [25]. Emmanual[26] also showed that
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the camels' rumen epithelium and liver oxidized negligible quantities of butyrate incompletely
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into ketone bodies or completely into CO2, whereas the camel kidney in contrast to the true
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ruminant kidney oxidized ketone bodies to a large extent.
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BOHB did, however, increase in llamas when fed the LP diet and to concentrations almost
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similar to those found in goats. This suggests that llamas are capable of producing BOHB just as
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the true ruminants as a result of hepatic ketogenesis, during a feeding associated with increased
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plasma concentrations of NEFA due to mobilization of body fat. This process is likely to be
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efficiently suppressed during more favorable nutrition conditions in llamas due to higher plasma
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concentrations of glucose and insulin, which will suppress adipose lipolysis and associated
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hepatic ketogenesis[27] just as in the true ruminants, and due to the generally lower amounts of
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mobilizable body fat in llamas. Thus, BOHB concentrations in llamas appear to reflect hepatic
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ketogenesis and thus metabolic state of the animal, unlike the true ruminants, where BOHB is
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highly influenced by foregut fermentation.
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Conclusions
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The very high plasma glucose concentrations in llamas co-existing with high insulin
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concentrations are indicators of an insulin resistant phenotype. The high plasma concentration of
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glucose might partly explain why llamas have lower energy expenditure and fat deposition
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compared to the small ruminant. Ability to uphold high plasma urea concentrations and
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particularly plasma creatinine concentrations on low protein diets, whilst reducing urinary
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nitrogen excretion, must reflect additional distinct adaptations of intermediary nitrogen
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metabolism possible at the renal excretory concentration. This would presumably result in more
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efficient recycling of nitrogen to sustain foregut fermentation on such diets. Together, these
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features may have been essential to improve the chances of survival of llamas in the harsh
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environments.
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Acknowledgments
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The present project was funded by the Danish Research Council for Development Research.
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The authors wish to thank guest researcher Mr. Einstein Tejada, lab technicians Ruth Jensen and
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Vibeke G. Christensen, and animal care taker Dennis S. Jensen, and the farm staff for expert
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technical assistance.
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[25] Chandrasena LG, Emmanuel B, Hamar DW, Howard BR. A comparative study of ketone body metabolism between the camel (Camelus dromedarius) and the sheep (Ovis aries). Comp Biochem Physiol B Comp Biochem. 1979; 64:109-112. [26] Emmanuel B. Oxidation of butyrate to ketone bodies and CO2 in the rumen epithelium, liver, kidney, heart and lung of camel (Camelus dromedarius), sheep (Ovis aries) and goat (Carpa hircus). Comp Biochem Physiol B Comp Biochem. 1980; 65:699-704. [27] Berg JM, Tymoczko JL, Stryer L. Biochemistry. Liberary of Congress, 2006.
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Table 1 Daily dry matter, crude protein and energy intakes in llamas, sheep and goats fed either dried green grass hay with high protein (HP) content or grass seed straw with low protein (LP) content
Dry matter intake (g) 1736a 1406b 637d Crude protein intake (g)
a
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Gross energy (MJ) 32.7a a
94
c
66
cde
26.5b 12.0d 18.3c b
c
c
884c d
61
622d
67
*** *** ***
de
9.2
*** *** ***
1.3
*** *** ***
43
16.8c 11.8d c
d
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Digested energy (MJ) 20.8 16.0 7.5 7.3 6.0 2.6 1.1 *** *** ** Values are least squares means ± standard error of means (SEM); a,b,c Mean values within a row with different superscript letters were significantly different (P
