Importance of birthcoat for lamb survival and growth in the Romane sheep breed extensively managed on rangelands D. Allain, D. Foulquié, P. Autran, D. Francois and J. Bouix J ANIM SCI 2014, 92:54-63. doi: 10.2527/jas.2013-6660 originally published online December 23, 2013
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Importance of birthcoat for lamb survival and growth in the Romane sheep breed extensively managed on rangelands D. Allain,*1 D. Foulquié,§ P. Autran,§ D. Francois,* and J. Bouix* *INRA, UR631, SAGA, Chemin de borde rouge CS 52627, 31326 Castanet Tolosan, France; and §INRA, UE321, Domaine de la Fage, Saint Jean et Saint Paul, 12250 Roquefort-sur-Soulzon, France
ABSTRACT: The Romane sheep breed proved to be adapted to harsh conditions with high prolificacy and lamb survival in outdoor farming, even under bad climate conditions. This breed shows large variability in its fleece type at birth and it has been suggested that lamb survival could be related to birthcoat type. The aim of the present study was to: i) characterize the coat of the lamb at birth and quantify lamb survival in relation to the birthcoat type and its protective properties concerning heat loss in the Romane breed raised under permanent exposure outdoors from birth, and ii) estimate genetic parameters of birthcoat type in relation to lamb survival and live body weight. A total of 7,880 lambs from 104 sires and 1,664 dams were used in a 14-yr experiment. The pedigree file included 9,625 individuals over 15 generations. Birthcoat type, coat surface temperature, coat depth, lamb survival, and growth were measured from birth to weaning. Weather data (temperature, wind speed, relative humidity, and precipitation) were recorded daily during lambing time. Two types of coats were observed at birth: hairy coat (62.9% of lambs) with a long coat depth (average 23.3 mm) or woolly 1 (37.1% of lambs) with a short coat depth (average 8.3 mm).
Birthcoat type was an important factor affecting lamb survival and growth from birth in the Romane breed. Total mortality rate was significantly less in hairybearing coat lambs than in short-woolly coat ones: 7.0% vs. 9.6%, 11.6 % vs. 14.8%, and 15.7 % vs. 20.1 % at 2, 10, and 50 d, respectively, and the relative risks of death increased by 37%, 67%, and 46 % at 2, 10, and 50 d of age, respectively, in short-woolly lambs. At birth, a significant lower coat surface temperature, indicating less heat loss, was observed in long-hairy coat lambs compared with others (21.1°C vs. 26.1°C). Heavier body weights and better growth performances up to the age of 50 d were observed in long-hairy-bearing coat lambs. Lamb survival was positively correlated to weather conditions at lambing time in short-woolly lambs, whereas no relation was observed in hairy-coat lambs. Heritability estimate of birthcoat type (hairy or woolly) is high (0.88). Genetic correlations between birthcoat type, lamb survival, and live body weight at birth were positive and moderate, suggesting that it would be beneficial to take birthcoat into account as an adaptive trait in any genetic strategies for sheep production in harsh conditions on rangelands.
Keywords: birthcoat, body weight, coat surface temperature, growth rate, lamb survival, Romane sheep © 2014 American Society of Animal Science. All rights reserved. INTRODUCTION
J. Anim. Sci. 2014.92:54–63 doi:10.2527/jas2013-6660
properties. The Romane breed, a 50:50 composite breed between the Berrichon du Cher (meat breed) and Romanov (prolific breed with strong maternal ability) that was originally destined for intensive sheep production (Ricordeau et al., 1992), has proven to be very hardy and well adapted to harsh outdoor conditions (Molenat et al., 2005). The Romane breed shows high prolificacy and lamb survival in outdoor farming, even under bad climate conditions. Due to its parental origins, this breed shows large variability in its fleece type, from hairy, long wool type similar to the Romanov breed to
The sheep meat industry in France is currently changing and leaving intensive agricultural areas for less favorable lands without housing. However, sheep breeding in harsh conditions under permanent exposure outdoors requires animals with specific adaptive 1Corresponding
author: [email protected] Received May 2, 2013. Accepted November 12, 2013.
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Importance of birthcoat for lamb survival
the fine, medium crossbreed fleece of the Berrichon du Cher breed, which was infused with Merino during the late 18th century. Thus, at birth, a highly variable coat type from a short, woolly fleece up to a hairy, long coat can be observed in lambs. It has been suggested that birthcoat type had an impact on lamb survival in several breeds (Purser and Karam, 1967; Jacquin et al., 2002; Hatcher et al., 2009), which is a major trait of importance to sheep production in many parts of the world. The aim of the present study was to: i) characterize the coat of the Romane lamb at birth, and quantify lamb survival in relation to the birthcoat type and its protective properties concerning heat loss and resistance to climatic conditions, and ii) evaluate genetic variability of birthcoat type in relation to survival and growth traits in the Romane lamb born and raised outdoors. Material and methods Experimental Animals This experiment was licensed under the guidelines of the French Ministry of Agriculture and the National Committee of Animal Experimentation for animal research. Experimental Animals and Management The study was carried out at the INRA experimental farm of La Fage on the Causses-du-Larzac (43°55´07˝ N, 3°05´41˝ E), a calcareous plateau in southern of France. As previously described (Bouix et al., 2002), the main characteristic of this high altitude territory (800 m above sea level) is aridness. Despite an abundant annual rainfall of 1,000 mm, great permeability of the soil feeds deep subterranean rivers and yields arid growing conditions. Seasons are highly contrasted with cold winters, due to the altitude, and hot summers, due to the southern latitude. Intermediate seasons show extreme variations in temperature, wind, and rainfall. Romane ewes were kept outside as a single flock (350 ewes per year) on a dry steepe rangeland throughout the year, including the lambing period from late March to mid-April. Climate conditions at that period can abruptly vary from severe conditions of low temperature, wind, and rain, or snow, to warm and sunny conditions. Animals are grazed on the rangeland year round and received some feed supplements (roughage, concentrate) in the winter, as previously described (Bouix, 2002; Molenat et al., 2005). The breeding system is characterized by a short lambing period in outdoor conditions from late March to mid-April. For reproduction, AI was used on all ewes in November. Then, 2 weeks later, ewes were distributed in sire groups for natural mating of barren ewes so that the
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sire of each lamb was determined according to the date of birth. The mean litter size observed in the data set was 2.20 lambs born per litter with 20.4%, 46.0%, and 33.6% of the litters as single, double, and triple, respectively. Lambs were left outdoors at birth with their dam, except when a ewe was not completely able to raise her litter or when the litter size exceeded 2 and 3 lambs per primiparous and multiparous dam, respectively. Excess lambs were moved indoors and artificially reared. Lambs were weaned at ~85 d of age. Annual shearing time for ewes is the beginning of July. To take account of the between-year variability, and also to get a sufficient number of animals in the data set, the study lasted 14 years, from 1999 to 2012. Animal Data Recorded At birth, within the first 12 h, all lambs were weighed (at 100-g precision), gender determined, assessed for birthcoat type and measurements of coat depth, and coat surface temperature, with an infrared thermometer (Jacquin et al., 2002). The grading of birthcoat consisted of assigning lambs to 1 of the 9 grades, on the basis of the presence, distribution, density, and length of halo-hair and/or coarse guard hair, determining composition and structure of the coat at birth. The 9 grades are: single woolly coat without halo- or coarse hair having a length 100 lambs per sire family). Linear Models for Coat Depth and Coat Surface Temperature at Birth, and Weights and Growth Rate up to 50 d of Age A linear model was used to identify fixed effects significantly affecting variation of coat depth and coat surface temperature at birth, and variation of lamb weights and lamb growth rate from birth to 50 d of age. The general mixed model using ASREML Software (Gilmour et al., 2009) was (Model 1): Yijkmnpqr = µ + Ci + SXj + Bk + Am + YPn + Sp + Model [1] Lq + eijklmnpqr
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where Yijlmnpqr is the rth observation for the ith birthcoat type, jth gender, kth type of birth, mth age of dam, nth year of production, pth sire, and qth litter of dam; with µ the population mean; Ci the coat type at birth (i= short woolly or long hairy); SXj the gender effect (j= male or female); Bk the type of birth effect (k = 1, 2 or 3+); Am the age of dam effect (m = 5, from 1 to 5 yr and older); YPn the year of production effect (n = 14, from 1999 to 2012); Sp the sire random effect (p = 104), Lq the litter random effect (q = 3,579), and eijkmnpqr the random error. Coat surface temperature of lambs at birth was analyzed by including surface temperature of the cement roofing material as covariate in Model 1. Lamb live bodyweights at 10 (LBW10), 30 (LBW30), and 50 (LBW50) d of age, and average daily gain at 10 (ADG10), 30 (ADG30), and 50 (ADG50) d were analyzed by replacing the birth type effect (Bk) by a composite effect, combining type of birth and rearing type, or number of lambs suckling their dam (BRkl with k = 1, 2, or 3+ born lambs, and l = 1, 2, or 3 suckling lambs per dam). Logistic Regression of Survival Traits Because survival traits were coded as binary traits, a generalized linear model analysis was performed assuming a Bernoulli distribution of the data and using a logit link function. The same fixed effects used in the linear model (Model [1]) were fitted, except that a covariate effect of the weather principal component of the first 2 d of lamb life and a polynomial covariate effect of live body weight at birth were included in the generalized linear model (Model [2]), using the ASREML Package (Gilmour et al., 2009): Yijklmnpqr = µ + Ci + SXj + Bk + Al+ YPm + Sp + Lq + β1WPC + β2LBW0 +eijklmnpqr Model [2] where Yijklmnpqr is the rth observation for the ith birthcoat type, jth gender, kth type of birth, lth age of dam, mth year of production, pth sire, and qth litter; with µ the population mean; Ci the coat type at birth (i = short woolly or long hairy); SXj the gender effect (j= male or female); Bk a birth type effect (k = 1, 2, or 3+ born lambs); Al the age of dam effect (l = 5, from 1 to 5 yr and older); YPm the year of production effect (m = 14 from 1999 to 2012); Sp the sire random effect (p = 104); Lq the litter random effect (q = 3,579); WPC was a covariate effect of the weather principal component of the first 2 d of lamb life and β1 its regression coefficient; LBW0 were orthogonal polynomial (cubic) covariates of live body weight at birth of each lamb q and β2 their regression coefficients; and eijklmnpqr the random error.
In order to test any variation of lamb survival at 2 d of age, according to birthcoat type in relation to weather condition changes at birth, an alternative model similar to Model 2 was used (Model 2a), by combining the coat type effect and WPC covariate in a single covariate coat type-WPC effect (2 levels: 1 for each coat type). For lamb survival at 10, 30, and 50 d of age, the covariate weather component of the first 2 d of lamb life were removed from the analysis Model 2. Relative risks of death within fixed effect were then computed from the estimates of the ASREML solution files. Estimation of Genetic Parameters for Birthcoat Type, Lamb Survival, and Body Weights Genetic parameters for birthcoat type, survival traits, and live body weight at birth were estimated using the Threshold Model (TM) program (available at http://snp. toulouse.inra.fr/~alegarra), developed by Legarra et al. (2008) for their own research, according to methods proposed by Sorensen et al. (1995) and Van Tassel et al. (1998), and used in different publications (Legarra and Ugarte, 2005; Lopez de Maturana et al., 2007). The TM program uses a Bayesian analysis and performs numerical integration through the Gibbs sampler. A chain of 220,000 iterations was used, with a burn-in of 20,000 rounds and saving a sample every 100 iterations. The mean and standard deviation of the estimated marginal posterior density were used as estimate and standard errors of the genetic parameters of interest. To estimate genetic parameters, the same fixed effects, as previously described, were fitted in the model, using the animal and litter as random effects for all traits, and using a maternal genetic effect as additional random effect for live body weights. In a first step, univariate analyses were separately undertaken to estimate heritability of birthcoat type and survival at any age, from birth up to 50 d of age. Then genetic and phenotypic correlations for birthcoat type, lamb weights, and lamb survival at 2, 10, 30, and 50 d of age, respectively, were estimated, using a multivariate analysis with the same model as for univariate analysis. RESULTS Variability and Heritability Estimates of Birthcoat Type in the Romane Breed A total of 7,880 lambs from 104 sires were included in the data analysis. The size of sire family varies from 6 to 252 offspring, with a mean size of 75 lambs. The number of lambs observed at birth and distribution of lambs per birthcoat grade with mean coat depth are shown in Table 2. As the distributions of coat depth and birthcoat grade were very close to being bimodal, the distribution of birth-
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Figure 1. Percentage of lambs bearing a short-woolly coat (SWC) when dam bore a short-woolly (dam SWC) or a long-hairy coat (dam LHC) at birth within the 20 largest sire families (>100 lambs/sire family).
coat grade was transformed into a binary trait by combining grades 1 to 3 as a short-woolly coat (type1) and grades 4 to 9 as a long-hairy coat (type 2), as described Table 2. About 2/3 of Romane lambs had a long-hairy double coat at birth, characterized by a greater coat depth of 23.3 mm vs. 8.3 mm for lambs bearing a single woolly coat (Table 2). Large variations were observed within sire family. In large family sire (>100 lambs), the proportion of shortwoolly lambs varied from 5.5% to 66.7%. Similarly, the distribution of birthcoat was significantly associated (P < 0.001) with the birthcoat type of the dam. A significantly larger proportion of short-woolly lambs was observed in large family sire when the dam had a woolly coat at birth compared with other dams (Fig. 1). The heritability estimates of birthcoat type and coat depth at birth were very high: 0.69 ± 0.03, 0.87 ± 0.01, and 0.75 ± 0.03 for coat type, when considered as a normal and binary trait, and coat depth, respectively (Table 3).
Relations between Birthcoat Type, Lamb Survival, Heat Losses, and Resistance to Climatic Conditions The percentage of lamb survival from birth up to 50 d of age, according to birthcoat type, is given in Table 4. Logistic regression analyses demonstrated that lamb survival was clearly affected by live body weight at birth (P < 0.001), birthcoat type (P < 0.001), gender (P < 0.001), litter size (P < 0.001; Table 5), and age of dam (P < 0.01; not reported in Table 5). Birthcoat type was an important factor affecting lamb survival from birth in the Romane breed. Lambs bearing a short-woolly coat at birth survived significantly (P < 0.001) less than others and total lamb survival rate up to 50 d of age was significantly greater (P 0.05); * P ≤ 0.05; ** P ≤ 0.01; *** P ≤ 0.001. 2Unit of 0.1-kg body weight increase (correspond to precision of weight measure).
relative risks of death increased by 43%, 71%, 57%, and 50 %, at 2, 10, 30, and 50 d of age, respectively, in short-woolly lambs compared with others. Live body weight at birth was also an important component of lamb survival. The relative risk of death increased significantly (P < 0.001), by >10%, when birth weight decreased (Table 5). Optimal survival was observed when birth weight was ~4 kg, whereas lambs having very light and very heavy weights had lower survival rates. A significant difference (P < 0.001) in coat surface temperature was observed, according to birthcoat type (Table 6). Lambs bearing a long-hairy coat had a coat surface temperature of 5.1°C less than that for shortwoolly fleece, indicating less heat loss and better coat protection than lambs having a short-woolly fleece. The protective role of the long-hairy coat was strengthened by analyzing lamb survival at 2 d, according to Model 2a. A significant effect (P < 0.01) of the weather principal component of the 2 first days of lamb life on survival at 2 d of age was observed on short-woolly bearing lambs, whereas no effect was observed on other lambs Table 7. Relative risks of death at 2 d of age, according to weather conditions and birthcoat type in the Romane breed. Relative risks of death were estimated as odds ratios computed from logistic regression (from logistic regression Model 2a). Age of lambs 2d
Short-woolly coat lambs 1.171
Long-hairy coat lambs 0.96
1These risks are significantly different (P ≤ 0.01) from 1 and correspond to a significant decrease of 1 unit of the weather principal component of the 2 first days of lamb life.
Table 6. Number of observations, mean (with residual standard deviation), test of significance and estimate (with standard error) of coat depth (mm), and coat surface temperature (°C) at birth in relation to birthcoat type at birth in the Romane breed (from linear model Model 1) Number of observations Mean (relative SD) Birthcoat type effect Long hairy - short woolly 1These
Coat depth, mm 7,780 17.9 (4.7) P ≤ 0.001 14.7 (0.2)1
Coat surface temperature, °C 7,780 23.7 (2.0) P ≤ 0.001 –5.1 (0.1)1
estimates are significantly (P ≤ 0.001) different from zero.
(Table 7). The relative risk of death is significantly increased under cold, wet, and windy weather conditions. There was a 17 % increase in mortality per 1 unit decrease of the weather principal component (Tables 1 and 7 for weather conditions and risk of death, respectively) in short-woolly lambs. Relationship between Birthcoat Type, Body Weight, and Growth Traits The variability of body weight and growth rate, according to birthcoat type, is presented in Table 8. Body weight and average daily growth rate were clearly affected by birthcoat type. A significantly heavier live body weight at birth (P < 0.001) was observed in long-hairy coat lambs. Such significant differences were still observed up to 50 d of age (Table 8). A significantly greater average daily growth rate (P < 0.001) was observed at any of the 3 periods (0 to 10, 10 to 30, and 30 to 50 d) from birth up to 50 d of age in long-hairy coat lambs (Table 8). Genetic Parameter Estimates of Birthcoat Type, Lamb Survival, and Growth Traits The heritability, genetic and phenotypic correlations between birthcoat type and total lamb survival at specific ages from birth onwards estimated using TM software are Table 8. Estimates of differences (standard errors in brackets) between long-hairy and short-woolly lambs in live body weight at different ages from birth and average daily growth rate of lambs at consecutive periods from birth (from the linear Model 1)
Live body weight (kg) At birth At 10 d At 30 d At 50 d Average daily growth rate (g) From birth to 10 d From 10 to 30 d From 30 to 50 d
n
Birth coat type difference Long-hairy to short-woolly coat
7,880 5,165 5,089 5,058
0.06 (0.02) 0.11 (0.03) 0.24 (0.05) 0.39 (0.07)
5,165 5,089 5,058
5.3 (1.9) 7.0 (1.5) 5.5 (1.5)
All estimates are significantly different (P > 0.001) from zero for each age.
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Table 9. Direct heritability (h²) of total survival traits up to specific ages and genetic correlations (rg; with standard errors) and phenotypic correlations (rp; with standard errors) with birthcoat type estimated using Threshold Model Specific age
Total lamb Survival h²
Genetic correlation rg
Phenotypic correlation rp
At 2 d At 10 d At 30 d At 50 d
0.10 ± 0.05 0.05 ± 0.03 0.04 ± 0.02 0.03 ± 0.02
0.38 ± 0.20 0.34 ± 0.22 0.50 ± 0.20 0.47 ± 0.22
0.12 ± 0.03 0.13 ± 0.03 0.13 ± 0.03 0.11 ± 0.02
presented in Table 9. The heritability estimates of total lamb survival from birth onward were low: 0.10 (±0.05), 0.05 (±0.03), 0.04 (±0.02) and 0.03 (±0.02) at 2, 10, 30, and 50 d of age, respectively. The genetic correlations between birthcoat type and lamb survival ranged from 0.34 to 0.50, indicating moderate positive correlations. Table 10 shows heritability estimates, genetic and phenotypic correlations between birthcoat type, survival at 2 d, and lamb weight (direct and maternal genetic component) at birth. Heritability and maternal genetic estimates of lamb weight at birth were moderate, 0.25 and 0.26, respectively. Genetic correlations between birthcoat type and birth weight (direct and maternal) were low and close to zero. Weak to strong favorable genetic correlations were observed between birthcoat type and survival, and birth weight (direct and maternal genetic) and survival at 2 d, 0.19, 0.53, and 0.55, respectively. DISCUSSION Birthcoat type is extremely variable in the Romane breed. About 2/3 of Romane lambs had a long-hairy double coat at birth with a deep coat depth (23 mm), whereas other lambs had a short-woolly coat with a short coat depth (8 mm). This variability originates from parental origins. The Romane breed is a 50:50 composite breed between the Berrichon du Cher, a medium wool breed that was crossed with Rambouillet Merino in the late 18th century, and the Romanov breed, known to have a hairy, double-coat fleece. Selection objectives of the Romane breed, considered as a new breed at the fourth intercross generation (Ricordeau et al., 1992), are mostly maternal (prolificacy, growth of the lambs between 10 and 30 d) and meat production traits, and any selection on wool traits is unlikely to have deliberately been undertaken. A large variability of the type of coat at birth was observed. The distributions of coat depth at birth and birthcoat grades are near bimodal so that a birthcoat type can be easily assessed as a binary trait. A large variability of birthcoat type was observed within sire family and according to the birthcoat type of the dam. Heritability estimates of birthcoat type and
Table 10. Direct heritability of birthcoat, survival at 2 d, birth lamb weight, and maternal heritability of birth lamb weight (on diagonal), genetic correlations (above), and phenotypic correlations (below) between birthcoat type, survival at 2 d, and lamb weight at birth using Threshold Model
Birthcoat type Survival at 2 d Weight at birth (direct genetic) Weight at birth (maternal genetic)
Birthcoat Survival type at 2 d 0.88 0.19 0.11 0.12 0.01 0.29
Weight at birth Weight at birth direct genetic (maternal genetic) –0.06 0.09 0.53 0.55 0.25 –0.26 0.26
coat depth at birth were very high. These estimates are in agreement with previous estimates of the Romane breed (Allain et al., 2009). High heritability estimates of birthcoat score were also observed in Merino sheep (Morley, 1955; Schinckel, 1955; Gregory, 1982; Ponzoni et al., 1997). Previous studies in the New Zealand Romney sheep have suggested that birthcoat hairiness is under the control of both dominant and recessive major genes (Dry, 1956; Dry, 1958). The QTL affecting staple length and coat structure have been reported in the Romane breed (Allain et al., 1998; Ponz et al., 2001) and in a Sarda– Lacaune backcross experimental design (Allain et al., 2006). Our results with a high heritability estimate, a near bimodal distribution of coat depth and birthcoat grades as well as distribution of birthcoat type according to sire family and birthcoat type of the dam, support these findings and it could be suggested that the variability in birthcoat type is under the control of a few major genes. Birthcoat type is an important factor affecting lamb survival from birth in the Romane breed. Lambs bearing a short-woolly coat at birth survived significantly (P < 0.001) less than others and total lamb survival rate up to 50 d of age was significantly greater (P < 0.001) in lambs bearing a long-hairy coat at birth. The relative risks of death increased by 43%, 71%, 57%, and 50 % at 2, 10, 30, and 50 d of age, respectively, in short-woolly lambs compared with others. A more detailed analysis of lamb survival on live lambs at 2 and 10 d of age showed that relative risk of death was significantly greater in lambs bearing a short-woolly coat at 10 and 30 d of age, respectively. Thus, the protective effect of a long-hairy coat on lamb survival remained significant up to 30 d of age. Thereafter, there were no significant differences in survival of live lambs at 30 d of age, according to birthcoat type. Contradictory results were reported on the relationship between lamb survival and birthcoat type. In Merino lambs, it has been reported that lamb survival was not highly related to the birthcoat type (Cloete et al., 2009; Hatcher et al., 2009), whereas a significant effect of birthcoat type on lamb survival up to a few weeks
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Importance of birthcoat for lamb survival
of age were observed in Welsh mountain sheep (Purser and Karam, 1967) and in different breeds and crossbred sheep (Jacquin et al., 2002). The variability of birthcoat type in Merino is less important than in Romane and Welsh mountain sheep breeds; this could explain the different results. The difference in lamb survival, according to birthcoat type, was correlated to a significant difference in coat surface temperature at birth. Lambs bearing a long-hairy coat had a coat surface temperature of 5.1°C less than that for short-woolly fleece, indicating less heat loss and a better coat protection than lambs having a short-woolly fleece. Such a difference in coat surface temperature could explain the difference observed in lamb survival, according to birthcoat type. Furthermore, lambs bearing a hairy coat at birth have heavier body weights and a better daily growth rate from birth up to 50 d of age. Similar results on growth rate were observed in the Welsh mountain sheep (Purser et Karam, 1967). These results are in accordance with the protective effect of birthcoat type on lamb survival. It can be assumed that lambs bearing a long-hairy coat and having a better coat protection and reduced heat losses were using a larger part of energy intake for growth, rather than maintaining body temperature and survival. The protective role of the long-hairy coat is also efficient against variation in climate conditions at birth. Several weather variables were recorded at daily intervals during lambing time. As weather data were significantly and highly correlated, a principal component analysis was performed to summarize weather conditions of the first 2 d of life of a lamb. A single continuous variable was used as a covariate in order to analyze the effect of weather conditions on lamb survival at 2 d of age. A significant increase in mortality was observed under cold, wet, and windy weather conditions in short-woolly lambs at 2 d of age, whereas no variation, according to weather conditions, was observed in long-hairy lambs. These results support findings in Merinos showing that fine-coated lambs had a much greater rate of heat loss under severe conditions of cold temperature, wind, and rain (Alexander, 1958), or with lower surviving ability of lambs when weather conditions are severe (Mullaney, 1966). Slee et al. (1991) reported similar results with a strong positive relationship between a hairy coat and cold resistance in newborn Merino lambs. When a lamb cannot maintain body temperature, its chance of survival is markedly reduced. Body temperature was not measured in this study, but it could be easily assumed that lambs bearing a short-woolly coat were generating more heat loss than long-hairy lambs and thus could not maintain their body temperature as easily as lambs bearing a long-hairy coat under severe weather conditions. The heritability estimates of total lamb survival from birth onward were low and decreased with age
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of lambs (from 0.10 at 2 d to 0.03 at 50 d). These low estimates are in agreement with results in other sheep breeds (Riggio et al., 2008; Matos et al. 2000; Sawalha et al., 2007; Cloete et al., 2009; Safari et al., 2005; Hatcher et al., 2010). The heritability estimate of survival is greatest at 2 d and then decreases thereafter. This trend strengthens the importance of birthcoat as it can be presumed that its decreasing effect with age as the coat is developing with better protective properties becomes less important and other random factors lead to mortality. Heritability and maternal genetic estimates of lamb weight at birth were moderate (0.25 and 0.26, respectively) and in agreement with previous studies (Safari et al., 2005; Riggio et al., 2008). Genetic correlations between birthcoat type and birth weight (direct and maternal) were low and close to zero, whereas low to strong favorable genetic correlations were observed between birthcoat type and survival at 2 d, and between birth weight (direct and maternal genetic) and survival at 2 d (0.19, 0.53 and 0.55, respectively), indicating that coat type and lamb weight at birth are not genetically related and could be both used as selection criteria to improve survival and lamb production. Genetic correlations between birthcoat type and total lamb survival at any age ranged from 0.34 to 0.50, indicating moderate positive correlations. Very few data about genetic correlation between lamb survival and birthcoat type are available. A low positive genetic correlation between birthcoat score and lamb survival up to weaning was reported in Merino and some crossbred Merino in Australia, suggesting that birthcoat score could add useful information as selection criteria to improve lamb survival (Brien et al., 2010). A high positive genetic correlation between birthcoat type and cold resistance was observed in newborn Merino lambs (Slee et al., 1991). Results of the present study clearly demonstrated the importance of birthcoat type for lamb survival. Thus, any selection to obtain a hairy coat at birth, which is a highly heritable trait, will result in a stronger aptitude for lambs to survive. Rapid progress could be easily obtained, whether or not the variability of birthcoat is under the control of a few major genes, as birthcoat type can be easily scored at birth. Results of the present study clearly demonstrated the importance of birthcoat type for lamb survival and gave important information about the essential role of a long-hairy birthcoat and its positive consequences on survival rate, heat body loss, and growing performance. Considerations about any disadvantage of a long-hairy birthcoat on fleece quality in the adult and therefore its commercial value can be easily avoided. Within European sheep farming, the value of raw wool is very low and the income from wool is often less than shearing costs.
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Conclusion Under harsh environment and permanent exposure outdoors on rangelands, lambs bearing a hairy birthcoat are more adapted to survive, especially around lambing time, and show better growth performance, up to weaning, than lambs bearing a fine and short-woolly coat. The birthcoat plays an essential role concerning heat body loss. Consequently, structure and composition of the birthcoat have to be considered in any genetic strategy for sheep meat production under harsh environmental conditions. The choice of a well-adapted breed or crossbred animals remains a key question. A selection program aiming at increasing coat hairiness at birth has to be developed and could be easily achieved through any classical phenotypic selection, as birthcoat type is a strongly heritable trait that can be easily scored at birth. LITERATURE CITED Alexander, G. 1958. Heat production of newborn lambs in relation to type of birthcoat. Proc. Aust. Soc. Anim. Prod. 2:10–14. Allain, D., D. Foulquié, D. François, P. Autran, B. Bibé, and J. Bouix. 2009. The birthcoat type: An important component of lamb survival in the French Romane breed raised under permanent exposure outdoors. In: Book of abstracts. 60th Annu. Meet. EAAP, Barcelona, Spain. Abstract 257. Allain, D., I. Lantier, J. M. Elsen, D. François, J. C. Brunel, J. L. Weisbecker, L. Schibler, D. Vaiman, E. P. Cribiu, A. Gautier, P. Berthon, and F. Lantier. 1998. A design aiming at detecting QTL controlling wool traits and other traits in the Inra401 sheep line. In: Proc. 6th World Cong. Genet. Appl. Livest. Prod., Armidale, NSW Australia. 24:51–54. Allain, D., L. Schibler, L. Mura, F. Barillet, T. Sechi, R. Rupp, S. Casu, E. P. Cribiu, and A. Carta. 2006. QTL detection with DNA markers for wool traits in a sheep backcross Sarda × Lacaune resource population. In: Proc. 8th World Cong. Genet. Appl. Livest. Prod., Belo Horizonte, MG, Brazil. Communication No. 05–07. Bouix, J., M. Jacquin, D. Foulquié, P. Autran, P. Guillouet, D. Hubert, and B. Bibe. 2002. Genetic effects on sheep production in harsh environment and extensive management system. In: Proc. 7th World Cong. Genet. Appl. Livest. Prod., Montpellier, France. 29:441–444. (Communication No. 02–02) Brien, F. D., M. L. Hebart, D. H. Smith, J. E. Hocking Edwards, J. C. Greef , K. W. Hart, G. Refshauge, T. L. Birt-Gardiner, G. Gaunt, R. Behrendt, M. W. Robertson, G. N. Hinch, K. G. Geenty, and J. H. J. van der Werf. 2010. Opportunities for genetic improvement of lamb survival. Anim. Prod. Sci. 50:1017–1050. Cloete, S. W. P., I. Misztal, and J. J. Olivier. 2009. Genetic parameters and trends for lamb survival and birth weight in a Merino flock divergently selected for multiple rearing ability. J. Anim. Sci. 87(7):21962–208. Dry, F. W. 1956. Twenty-five years of Mendelian sheep breeding. Proc. N. Z. Soc. Anim. Prod. 16:130–140. Dry, F. W. 1958. Further breeding experiments with New Zealand Romney N-type sheep to 1956. Aust. J. Agric. Res. 9:348–360. Gilmour, A. R., B. J. Gogel, B. R. Cullis, and R. Thompson, 2009. ASREML User guide manual. Release 3.0. Orange 2800 Australia, NSW Agriculture. Gregory, I. P. 1982. Genetic studies of South Australian Merino sheep. III Heritabilities of various wool and body traits. Aust. J. Agric. Res. 33:355–362.
Hatcher, S., K. D. Atkins, and E. Safari. 2009. Phenotypic aspects of lamb survival in Australian Merino sheep. J. Anim. Sci. 87(9):2781–2790. Hatcher, S., K. D. Atkins, and E. Safari. 2010. Lamb survival in Australian Merino Sheep: A genetic analysis. J. Anim. Sci. 88(10):3198–3205. Jacquin, M., D. Allain, J. Bouix, D. Foulquié, P. Autran, and B. Bibe. 2002. Lamb survival, coat surface temperature and growing performances in relation to birthcoat type among different genotypes raised outdoors. In: Proc. 7th World Cong. Genet. Appl. Livest. Prod., Montpellier, France. 32:379-382. (Communication No. 18-13) Legarra, A., and E. Ugarte, 2005. Genetic parameters of udder traits, somatic cell score, and milk yield in Latxa sheep. J. Dairy Sci. 88(6):2228–2245. Legarra, A., L. Varona, and E. Lopez de Maturana. 2008. TM Threshold Model Version 4. http://genoweb.toulouse.inra. fr/~alegarra. (Accessed 3 Aug. 2011). Lopez de Maturana, E., A. Legarra, L. Varona, and E. Ugarte, 2007. Analysis of fertility and dystocia in Holsteins using recursive models to handle censored and categorical data. J. Dairy Sci. 90(4):2012–2024. Matos, C. A. P., D. L. Thomas, L. D. Young, and D. Gianola. 2000. Genetic analyses of lamb survival in Rambouillet and Finnsheep flocks by linear and threshold models. Anim. Sci. 71(2):227–234. Molenat, G., D. Foulquié, P. Autran, J. Bouix, D. Hubert, M. Jacquin, F. Bocquier, and B. Bibe. 2005. Pour un élevage ovin allaitant performant et durable sur parcours: un système expérimental sur le Causse du Larzac. INRA Prod. Anim. 18(5):323–328. Morley, F. H. W. 1955. Selection for economic characters in Australian Merino sheep. V. Further estimates of phenotypic and genetic parameters. Aust. J. Agric. Res. 6:77–90. Mullaney, P. D. 1966. The relation of birthcoat and lamb survival. Aust. J. Exp.. Agric. Anim. Husb. 6:84–87. Ponz, R., C. Moreno, D. Allain, J. M. Elsen, F. Lantier, I. Lantier, J. C. Brunel, and M. Pérez-Enciso. 2001. Assessment of genetic variation explained by markers for wool traits in sheep via a segment mapping approach. Mam. Genome. 12(7):569–572. Ponzoni, R.W., R. J. Grimson, K. S. Jaensch, D. H. Smith, and P. I. Hynd. 1997. Birthcoat: Is it worth taking it into considerations in Merino sheep genetic improvement programs? Wool Tech. Sheep Breed. 45(1):12–26. Purser, A. F., and H. A. Karam. 1967. Lamb survival, growth and fleece production in relation to birthcoat among Welsh mountain sheep. Anim. Prod. 9:75–85. Ricordeau, G., L. Tchamitchian, J. C. Brunel, T. C. Nguyen, and D. François. 1992. La race ovine INRA 401: Un exemple de souche synthétique. INRA Prod. Anim. hors-série: Eléments de génétique quantitative 5:255–262. Riggio, V., R. Finocchiaro, and S. C. Bishop, 2008. Genetic parameters for early lamb survival and growth in Scottish Blackface sheep. J. Anim. Sci. 86(8):1758–1764. Safari, E., N. M. Fogarty, and A. R. Gilmour. 2005. A review of genetic parameter estimates for wool, growth, meat and reproduction traits in sheep. Livest. Prod. Sci. 92(3):271–289. Sawalha, R. M., J. Conington, S. Brotherstone, and B. Villanueva. 2007. Analyses of lamb survival of Scottish Blackface sheep. Animal 1:151–157. Schinckel, P. G. 1955. Inheritance of birthcoat in a strain of Merino sheep. Aust. J. Agric. Res. 6:595–607. Slee, J., R. L. Alexander, R. Bradley, N. Jackson, and D. Stevens. 1991. Genetic aspects of cold resistance and related character in newborn Merino lambs. Aust. J. Exp. Agric. 31:175–182.
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References
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Importance of birthcoat for lamb survival and growth in the Romane sheep breed extensively managed on rangelands D. Allain,*1 D. Foulquié,§ P. Autran,§ D. Francois,* and J. Bouix* *INRA, UR631, SAGA, Chemin de borde rouge CS 52627, 31326 Castanet Tolosan, France; and §INRA, UE321, Domaine de la Fage, Saint Jean et Saint Paul, 12250 Roquefort-sur-Soulzon, France
ABSTRACT: The Romane sheep breed proved to be adapted to harsh conditions with high prolificacy and lamb survival in outdoor farming, even under bad climate conditions. This breed shows large variability in its fleece type at birth and it has been suggested that lamb survival could be related to birthcoat type. The aim of the present study was to: i) characterize the coat of the lamb at birth and quantify lamb survival in relation to the birthcoat type and its protective properties concerning heat loss in the Romane breed raised under permanent exposure outdoors from birth, and ii) estimate genetic parameters of birthcoat type in relation to lamb survival and live body weight. A total of 7,880 lambs from 104 sires and 1,664 dams were used in a 14-yr experiment. The pedigree file included 9,625 individuals over 15 generations. Birthcoat type, coat surface temperature, coat depth, lamb survival, and growth were measured from birth to weaning. Weather data (temperature, wind speed, relative humidity, and precipitation) were recorded daily during lambing time. Two types of coats were observed at birth: hairy coat (62.9% of lambs) with a long coat depth (average 23.3 mm) or woolly 1 (37.1% of lambs) with a short coat depth (average 8.3 mm).
Birthcoat type was an important factor affecting lamb survival and growth from birth in the Romane breed. Total mortality rate was significantly less in hairybearing coat lambs than in short-woolly coat ones: 7.0% vs. 9.6%, 11.6 % vs. 14.8%, and 15.7 % vs. 20.1 % at 2, 10, and 50 d, respectively, and the relative risks of death increased by 37%, 67%, and 46 % at 2, 10, and 50 d of age, respectively, in short-woolly lambs. At birth, a significant lower coat surface temperature, indicating less heat loss, was observed in long-hairy coat lambs compared with others (21.1°C vs. 26.1°C). Heavier body weights and better growth performances up to the age of 50 d were observed in long-hairy-bearing coat lambs. Lamb survival was positively correlated to weather conditions at lambing time in short-woolly lambs, whereas no relation was observed in hairy-coat lambs. Heritability estimate of birthcoat type (hairy or woolly) is high (0.88). Genetic correlations between birthcoat type, lamb survival, and live body weight at birth were positive and moderate, suggesting that it would be beneficial to take birthcoat into account as an adaptive trait in any genetic strategies for sheep production in harsh conditions on rangelands.
Keywords: birthcoat, body weight, coat surface temperature, growth rate, lamb survival, Romane sheep © 2014 American Society of Animal Science. All rights reserved. INTRODUCTION
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properties. The Romane breed, a 50:50 composite breed between the Berrichon du Cher (meat breed) and Romanov (prolific breed with strong maternal ability) that was originally destined for intensive sheep production (Ricordeau et al., 1992), has proven to be very hardy and well adapted to harsh outdoor conditions (Molenat et al., 2005). The Romane breed shows high prolificacy and lamb survival in outdoor farming, even under bad climate conditions. Due to its parental origins, this breed shows large variability in its fleece type, from hairy, long wool type similar to the Romanov breed to
The sheep meat industry in France is currently changing and leaving intensive agricultural areas for less favorable lands without housing. However, sheep breeding in harsh conditions under permanent exposure outdoors requires animals with specific adaptive 1Corresponding
author: [email protected] Received May 2, 2013. Accepted November 12, 2013.
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Importance of birthcoat for lamb survival
the fine, medium crossbreed fleece of the Berrichon du Cher breed, which was infused with Merino during the late 18th century. Thus, at birth, a highly variable coat type from a short, woolly fleece up to a hairy, long coat can be observed in lambs. It has been suggested that birthcoat type had an impact on lamb survival in several breeds (Purser and Karam, 1967; Jacquin et al., 2002; Hatcher et al., 2009), which is a major trait of importance to sheep production in many parts of the world. The aim of the present study was to: i) characterize the coat of the Romane lamb at birth, and quantify lamb survival in relation to the birthcoat type and its protective properties concerning heat loss and resistance to climatic conditions, and ii) evaluate genetic variability of birthcoat type in relation to survival and growth traits in the Romane lamb born and raised outdoors. Material and methods Experimental Animals This experiment was licensed under the guidelines of the French Ministry of Agriculture and the National Committee of Animal Experimentation for animal research. Experimental Animals and Management The study was carried out at the INRA experimental farm of La Fage on the Causses-du-Larzac (43°55´07˝ N, 3°05´41˝ E), a calcareous plateau in southern of France. As previously described (Bouix et al., 2002), the main characteristic of this high altitude territory (800 m above sea level) is aridness. Despite an abundant annual rainfall of 1,000 mm, great permeability of the soil feeds deep subterranean rivers and yields arid growing conditions. Seasons are highly contrasted with cold winters, due to the altitude, and hot summers, due to the southern latitude. Intermediate seasons show extreme variations in temperature, wind, and rainfall. Romane ewes were kept outside as a single flock (350 ewes per year) on a dry steepe rangeland throughout the year, including the lambing period from late March to mid-April. Climate conditions at that period can abruptly vary from severe conditions of low temperature, wind, and rain, or snow, to warm and sunny conditions. Animals are grazed on the rangeland year round and received some feed supplements (roughage, concentrate) in the winter, as previously described (Bouix, 2002; Molenat et al., 2005). The breeding system is characterized by a short lambing period in outdoor conditions from late March to mid-April. For reproduction, AI was used on all ewes in November. Then, 2 weeks later, ewes were distributed in sire groups for natural mating of barren ewes so that the
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sire of each lamb was determined according to the date of birth. The mean litter size observed in the data set was 2.20 lambs born per litter with 20.4%, 46.0%, and 33.6% of the litters as single, double, and triple, respectively. Lambs were left outdoors at birth with their dam, except when a ewe was not completely able to raise her litter or when the litter size exceeded 2 and 3 lambs per primiparous and multiparous dam, respectively. Excess lambs were moved indoors and artificially reared. Lambs were weaned at ~85 d of age. Annual shearing time for ewes is the beginning of July. To take account of the between-year variability, and also to get a sufficient number of animals in the data set, the study lasted 14 years, from 1999 to 2012. Animal Data Recorded At birth, within the first 12 h, all lambs were weighed (at 100-g precision), gender determined, assessed for birthcoat type and measurements of coat depth, and coat surface temperature, with an infrared thermometer (Jacquin et al., 2002). The grading of birthcoat consisted of assigning lambs to 1 of the 9 grades, on the basis of the presence, distribution, density, and length of halo-hair and/or coarse guard hair, determining composition and structure of the coat at birth. The 9 grades are: single woolly coat without halo- or coarse hair having a length 100 lambs per sire family). Linear Models for Coat Depth and Coat Surface Temperature at Birth, and Weights and Growth Rate up to 50 d of Age A linear model was used to identify fixed effects significantly affecting variation of coat depth and coat surface temperature at birth, and variation of lamb weights and lamb growth rate from birth to 50 d of age. The general mixed model using ASREML Software (Gilmour et al., 2009) was (Model 1): Yijkmnpqr = µ + Ci + SXj + Bk + Am + YPn + Sp + Model [1] Lq + eijklmnpqr
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where Yijlmnpqr is the rth observation for the ith birthcoat type, jth gender, kth type of birth, mth age of dam, nth year of production, pth sire, and qth litter of dam; with µ the population mean; Ci the coat type at birth (i= short woolly or long hairy); SXj the gender effect (j= male or female); Bk the type of birth effect (k = 1, 2 or 3+); Am the age of dam effect (m = 5, from 1 to 5 yr and older); YPn the year of production effect (n = 14, from 1999 to 2012); Sp the sire random effect (p = 104), Lq the litter random effect (q = 3,579), and eijkmnpqr the random error. Coat surface temperature of lambs at birth was analyzed by including surface temperature of the cement roofing material as covariate in Model 1. Lamb live bodyweights at 10 (LBW10), 30 (LBW30), and 50 (LBW50) d of age, and average daily gain at 10 (ADG10), 30 (ADG30), and 50 (ADG50) d were analyzed by replacing the birth type effect (Bk) by a composite effect, combining type of birth and rearing type, or number of lambs suckling their dam (BRkl with k = 1, 2, or 3+ born lambs, and l = 1, 2, or 3 suckling lambs per dam). Logistic Regression of Survival Traits Because survival traits were coded as binary traits, a generalized linear model analysis was performed assuming a Bernoulli distribution of the data and using a logit link function. The same fixed effects used in the linear model (Model [1]) were fitted, except that a covariate effect of the weather principal component of the first 2 d of lamb life and a polynomial covariate effect of live body weight at birth were included in the generalized linear model (Model [2]), using the ASREML Package (Gilmour et al., 2009): Yijklmnpqr = µ + Ci + SXj + Bk + Al+ YPm + Sp + Lq + β1WPC + β2LBW0 +eijklmnpqr Model [2] where Yijklmnpqr is the rth observation for the ith birthcoat type, jth gender, kth type of birth, lth age of dam, mth year of production, pth sire, and qth litter; with µ the population mean; Ci the coat type at birth (i = short woolly or long hairy); SXj the gender effect (j= male or female); Bk a birth type effect (k = 1, 2, or 3+ born lambs); Al the age of dam effect (l = 5, from 1 to 5 yr and older); YPm the year of production effect (m = 14 from 1999 to 2012); Sp the sire random effect (p = 104); Lq the litter random effect (q = 3,579); WPC was a covariate effect of the weather principal component of the first 2 d of lamb life and β1 its regression coefficient; LBW0 were orthogonal polynomial (cubic) covariates of live body weight at birth of each lamb q and β2 their regression coefficients; and eijklmnpqr the random error.
In order to test any variation of lamb survival at 2 d of age, according to birthcoat type in relation to weather condition changes at birth, an alternative model similar to Model 2 was used (Model 2a), by combining the coat type effect and WPC covariate in a single covariate coat type-WPC effect (2 levels: 1 for each coat type). For lamb survival at 10, 30, and 50 d of age, the covariate weather component of the first 2 d of lamb life were removed from the analysis Model 2. Relative risks of death within fixed effect were then computed from the estimates of the ASREML solution files. Estimation of Genetic Parameters for Birthcoat Type, Lamb Survival, and Body Weights Genetic parameters for birthcoat type, survival traits, and live body weight at birth were estimated using the Threshold Model (TM) program (available at http://snp. toulouse.inra.fr/~alegarra), developed by Legarra et al. (2008) for their own research, according to methods proposed by Sorensen et al. (1995) and Van Tassel et al. (1998), and used in different publications (Legarra and Ugarte, 2005; Lopez de Maturana et al., 2007). The TM program uses a Bayesian analysis and performs numerical integration through the Gibbs sampler. A chain of 220,000 iterations was used, with a burn-in of 20,000 rounds and saving a sample every 100 iterations. The mean and standard deviation of the estimated marginal posterior density were used as estimate and standard errors of the genetic parameters of interest. To estimate genetic parameters, the same fixed effects, as previously described, were fitted in the model, using the animal and litter as random effects for all traits, and using a maternal genetic effect as additional random effect for live body weights. In a first step, univariate analyses were separately undertaken to estimate heritability of birthcoat type and survival at any age, from birth up to 50 d of age. Then genetic and phenotypic correlations for birthcoat type, lamb weights, and lamb survival at 2, 10, 30, and 50 d of age, respectively, were estimated, using a multivariate analysis with the same model as for univariate analysis. RESULTS Variability and Heritability Estimates of Birthcoat Type in the Romane Breed A total of 7,880 lambs from 104 sires were included in the data analysis. The size of sire family varies from 6 to 252 offspring, with a mean size of 75 lambs. The number of lambs observed at birth and distribution of lambs per birthcoat grade with mean coat depth are shown in Table 2. As the distributions of coat depth and birthcoat grade were very close to being bimodal, the distribution of birth-
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Figure 1. Percentage of lambs bearing a short-woolly coat (SWC) when dam bore a short-woolly (dam SWC) or a long-hairy coat (dam LHC) at birth within the 20 largest sire families (>100 lambs/sire family).
coat grade was transformed into a binary trait by combining grades 1 to 3 as a short-woolly coat (type1) and grades 4 to 9 as a long-hairy coat (type 2), as described Table 2. About 2/3 of Romane lambs had a long-hairy double coat at birth, characterized by a greater coat depth of 23.3 mm vs. 8.3 mm for lambs bearing a single woolly coat (Table 2). Large variations were observed within sire family. In large family sire (>100 lambs), the proportion of shortwoolly lambs varied from 5.5% to 66.7%. Similarly, the distribution of birthcoat was significantly associated (P < 0.001) with the birthcoat type of the dam. A significantly larger proportion of short-woolly lambs was observed in large family sire when the dam had a woolly coat at birth compared with other dams (Fig. 1). The heritability estimates of birthcoat type and coat depth at birth were very high: 0.69 ± 0.03, 0.87 ± 0.01, and 0.75 ± 0.03 for coat type, when considered as a normal and binary trait, and coat depth, respectively (Table 3).
Relations between Birthcoat Type, Lamb Survival, Heat Losses, and Resistance to Climatic Conditions The percentage of lamb survival from birth up to 50 d of age, according to birthcoat type, is given in Table 4. Logistic regression analyses demonstrated that lamb survival was clearly affected by live body weight at birth (P < 0.001), birthcoat type (P < 0.001), gender (P < 0.001), litter size (P < 0.001; Table 5), and age of dam (P < 0.01; not reported in Table 5). Birthcoat type was an important factor affecting lamb survival from birth in the Romane breed. Lambs bearing a short-woolly coat at birth survived significantly (P < 0.001) less than others and total lamb survival rate up to 50 d of age was significantly greater (P 0.05); * P ≤ 0.05; ** P ≤ 0.01; *** P ≤ 0.001. 2Unit of 0.1-kg body weight increase (correspond to precision of weight measure).
relative risks of death increased by 43%, 71%, 57%, and 50 %, at 2, 10, 30, and 50 d of age, respectively, in short-woolly lambs compared with others. Live body weight at birth was also an important component of lamb survival. The relative risk of death increased significantly (P < 0.001), by >10%, when birth weight decreased (Table 5). Optimal survival was observed when birth weight was ~4 kg, whereas lambs having very light and very heavy weights had lower survival rates. A significant difference (P < 0.001) in coat surface temperature was observed, according to birthcoat type (Table 6). Lambs bearing a long-hairy coat had a coat surface temperature of 5.1°C less than that for shortwoolly fleece, indicating less heat loss and better coat protection than lambs having a short-woolly fleece. The protective role of the long-hairy coat was strengthened by analyzing lamb survival at 2 d, according to Model 2a. A significant effect (P < 0.01) of the weather principal component of the 2 first days of lamb life on survival at 2 d of age was observed on short-woolly bearing lambs, whereas no effect was observed on other lambs Table 7. Relative risks of death at 2 d of age, according to weather conditions and birthcoat type in the Romane breed. Relative risks of death were estimated as odds ratios computed from logistic regression (from logistic regression Model 2a). Age of lambs 2d
Short-woolly coat lambs 1.171
Long-hairy coat lambs 0.96
1These risks are significantly different (P ≤ 0.01) from 1 and correspond to a significant decrease of 1 unit of the weather principal component of the 2 first days of lamb life.
Table 6. Number of observations, mean (with residual standard deviation), test of significance and estimate (with standard error) of coat depth (mm), and coat surface temperature (°C) at birth in relation to birthcoat type at birth in the Romane breed (from linear model Model 1) Number of observations Mean (relative SD) Birthcoat type effect Long hairy - short woolly 1These
Coat depth, mm 7,780 17.9 (4.7) P ≤ 0.001 14.7 (0.2)1
Coat surface temperature, °C 7,780 23.7 (2.0) P ≤ 0.001 –5.1 (0.1)1
estimates are significantly (P ≤ 0.001) different from zero.
(Table 7). The relative risk of death is significantly increased under cold, wet, and windy weather conditions. There was a 17 % increase in mortality per 1 unit decrease of the weather principal component (Tables 1 and 7 for weather conditions and risk of death, respectively) in short-woolly lambs. Relationship between Birthcoat Type, Body Weight, and Growth Traits The variability of body weight and growth rate, according to birthcoat type, is presented in Table 8. Body weight and average daily growth rate were clearly affected by birthcoat type. A significantly heavier live body weight at birth (P < 0.001) was observed in long-hairy coat lambs. Such significant differences were still observed up to 50 d of age (Table 8). A significantly greater average daily growth rate (P < 0.001) was observed at any of the 3 periods (0 to 10, 10 to 30, and 30 to 50 d) from birth up to 50 d of age in long-hairy coat lambs (Table 8). Genetic Parameter Estimates of Birthcoat Type, Lamb Survival, and Growth Traits The heritability, genetic and phenotypic correlations between birthcoat type and total lamb survival at specific ages from birth onwards estimated using TM software are Table 8. Estimates of differences (standard errors in brackets) between long-hairy and short-woolly lambs in live body weight at different ages from birth and average daily growth rate of lambs at consecutive periods from birth (from the linear Model 1)
Live body weight (kg) At birth At 10 d At 30 d At 50 d Average daily growth rate (g) From birth to 10 d From 10 to 30 d From 30 to 50 d
n
Birth coat type difference Long-hairy to short-woolly coat
7,880 5,165 5,089 5,058
0.06 (0.02) 0.11 (0.03) 0.24 (0.05) 0.39 (0.07)
5,165 5,089 5,058
5.3 (1.9) 7.0 (1.5) 5.5 (1.5)
All estimates are significantly different (P > 0.001) from zero for each age.
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Table 9. Direct heritability (h²) of total survival traits up to specific ages and genetic correlations (rg; with standard errors) and phenotypic correlations (rp; with standard errors) with birthcoat type estimated using Threshold Model Specific age
Total lamb Survival h²
Genetic correlation rg
Phenotypic correlation rp
At 2 d At 10 d At 30 d At 50 d
0.10 ± 0.05 0.05 ± 0.03 0.04 ± 0.02 0.03 ± 0.02
0.38 ± 0.20 0.34 ± 0.22 0.50 ± 0.20 0.47 ± 0.22
0.12 ± 0.03 0.13 ± 0.03 0.13 ± 0.03 0.11 ± 0.02
presented in Table 9. The heritability estimates of total lamb survival from birth onward were low: 0.10 (±0.05), 0.05 (±0.03), 0.04 (±0.02) and 0.03 (±0.02) at 2, 10, 30, and 50 d of age, respectively. The genetic correlations between birthcoat type and lamb survival ranged from 0.34 to 0.50, indicating moderate positive correlations. Table 10 shows heritability estimates, genetic and phenotypic correlations between birthcoat type, survival at 2 d, and lamb weight (direct and maternal genetic component) at birth. Heritability and maternal genetic estimates of lamb weight at birth were moderate, 0.25 and 0.26, respectively. Genetic correlations between birthcoat type and birth weight (direct and maternal) were low and close to zero. Weak to strong favorable genetic correlations were observed between birthcoat type and survival, and birth weight (direct and maternal genetic) and survival at 2 d, 0.19, 0.53, and 0.55, respectively. DISCUSSION Birthcoat type is extremely variable in the Romane breed. About 2/3 of Romane lambs had a long-hairy double coat at birth with a deep coat depth (23 mm), whereas other lambs had a short-woolly coat with a short coat depth (8 mm). This variability originates from parental origins. The Romane breed is a 50:50 composite breed between the Berrichon du Cher, a medium wool breed that was crossed with Rambouillet Merino in the late 18th century, and the Romanov breed, known to have a hairy, double-coat fleece. Selection objectives of the Romane breed, considered as a new breed at the fourth intercross generation (Ricordeau et al., 1992), are mostly maternal (prolificacy, growth of the lambs between 10 and 30 d) and meat production traits, and any selection on wool traits is unlikely to have deliberately been undertaken. A large variability of the type of coat at birth was observed. The distributions of coat depth at birth and birthcoat grades are near bimodal so that a birthcoat type can be easily assessed as a binary trait. A large variability of birthcoat type was observed within sire family and according to the birthcoat type of the dam. Heritability estimates of birthcoat type and
Table 10. Direct heritability of birthcoat, survival at 2 d, birth lamb weight, and maternal heritability of birth lamb weight (on diagonal), genetic correlations (above), and phenotypic correlations (below) between birthcoat type, survival at 2 d, and lamb weight at birth using Threshold Model
Birthcoat type Survival at 2 d Weight at birth (direct genetic) Weight at birth (maternal genetic)
Birthcoat Survival type at 2 d 0.88 0.19 0.11 0.12 0.01 0.29
Weight at birth Weight at birth direct genetic (maternal genetic) –0.06 0.09 0.53 0.55 0.25 –0.26 0.26
coat depth at birth were very high. These estimates are in agreement with previous estimates of the Romane breed (Allain et al., 2009). High heritability estimates of birthcoat score were also observed in Merino sheep (Morley, 1955; Schinckel, 1955; Gregory, 1982; Ponzoni et al., 1997). Previous studies in the New Zealand Romney sheep have suggested that birthcoat hairiness is under the control of both dominant and recessive major genes (Dry, 1956; Dry, 1958). The QTL affecting staple length and coat structure have been reported in the Romane breed (Allain et al., 1998; Ponz et al., 2001) and in a Sarda– Lacaune backcross experimental design (Allain et al., 2006). Our results with a high heritability estimate, a near bimodal distribution of coat depth and birthcoat grades as well as distribution of birthcoat type according to sire family and birthcoat type of the dam, support these findings and it could be suggested that the variability in birthcoat type is under the control of a few major genes. Birthcoat type is an important factor affecting lamb survival from birth in the Romane breed. Lambs bearing a short-woolly coat at birth survived significantly (P < 0.001) less than others and total lamb survival rate up to 50 d of age was significantly greater (P < 0.001) in lambs bearing a long-hairy coat at birth. The relative risks of death increased by 43%, 71%, 57%, and 50 % at 2, 10, 30, and 50 d of age, respectively, in short-woolly lambs compared with others. A more detailed analysis of lamb survival on live lambs at 2 and 10 d of age showed that relative risk of death was significantly greater in lambs bearing a short-woolly coat at 10 and 30 d of age, respectively. Thus, the protective effect of a long-hairy coat on lamb survival remained significant up to 30 d of age. Thereafter, there were no significant differences in survival of live lambs at 30 d of age, according to birthcoat type. Contradictory results were reported on the relationship between lamb survival and birthcoat type. In Merino lambs, it has been reported that lamb survival was not highly related to the birthcoat type (Cloete et al., 2009; Hatcher et al., 2009), whereas a significant effect of birthcoat type on lamb survival up to a few weeks
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Importance of birthcoat for lamb survival
of age were observed in Welsh mountain sheep (Purser and Karam, 1967) and in different breeds and crossbred sheep (Jacquin et al., 2002). The variability of birthcoat type in Merino is less important than in Romane and Welsh mountain sheep breeds; this could explain the different results. The difference in lamb survival, according to birthcoat type, was correlated to a significant difference in coat surface temperature at birth. Lambs bearing a long-hairy coat had a coat surface temperature of 5.1°C less than that for short-woolly fleece, indicating less heat loss and a better coat protection than lambs having a short-woolly fleece. Such a difference in coat surface temperature could explain the difference observed in lamb survival, according to birthcoat type. Furthermore, lambs bearing a hairy coat at birth have heavier body weights and a better daily growth rate from birth up to 50 d of age. Similar results on growth rate were observed in the Welsh mountain sheep (Purser et Karam, 1967). These results are in accordance with the protective effect of birthcoat type on lamb survival. It can be assumed that lambs bearing a long-hairy coat and having a better coat protection and reduced heat losses were using a larger part of energy intake for growth, rather than maintaining body temperature and survival. The protective role of the long-hairy coat is also efficient against variation in climate conditions at birth. Several weather variables were recorded at daily intervals during lambing time. As weather data were significantly and highly correlated, a principal component analysis was performed to summarize weather conditions of the first 2 d of life of a lamb. A single continuous variable was used as a covariate in order to analyze the effect of weather conditions on lamb survival at 2 d of age. A significant increase in mortality was observed under cold, wet, and windy weather conditions in short-woolly lambs at 2 d of age, whereas no variation, according to weather conditions, was observed in long-hairy lambs. These results support findings in Merinos showing that fine-coated lambs had a much greater rate of heat loss under severe conditions of cold temperature, wind, and rain (Alexander, 1958), or with lower surviving ability of lambs when weather conditions are severe (Mullaney, 1966). Slee et al. (1991) reported similar results with a strong positive relationship between a hairy coat and cold resistance in newborn Merino lambs. When a lamb cannot maintain body temperature, its chance of survival is markedly reduced. Body temperature was not measured in this study, but it could be easily assumed that lambs bearing a short-woolly coat were generating more heat loss than long-hairy lambs and thus could not maintain their body temperature as easily as lambs bearing a long-hairy coat under severe weather conditions. The heritability estimates of total lamb survival from birth onward were low and decreased with age
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of lambs (from 0.10 at 2 d to 0.03 at 50 d). These low estimates are in agreement with results in other sheep breeds (Riggio et al., 2008; Matos et al. 2000; Sawalha et al., 2007; Cloete et al., 2009; Safari et al., 2005; Hatcher et al., 2010). The heritability estimate of survival is greatest at 2 d and then decreases thereafter. This trend strengthens the importance of birthcoat as it can be presumed that its decreasing effect with age as the coat is developing with better protective properties becomes less important and other random factors lead to mortality. Heritability and maternal genetic estimates of lamb weight at birth were moderate (0.25 and 0.26, respectively) and in agreement with previous studies (Safari et al., 2005; Riggio et al., 2008). Genetic correlations between birthcoat type and birth weight (direct and maternal) were low and close to zero, whereas low to strong favorable genetic correlations were observed between birthcoat type and survival at 2 d, and between birth weight (direct and maternal genetic) and survival at 2 d (0.19, 0.53 and 0.55, respectively), indicating that coat type and lamb weight at birth are not genetically related and could be both used as selection criteria to improve survival and lamb production. Genetic correlations between birthcoat type and total lamb survival at any age ranged from 0.34 to 0.50, indicating moderate positive correlations. Very few data about genetic correlation between lamb survival and birthcoat type are available. A low positive genetic correlation between birthcoat score and lamb survival up to weaning was reported in Merino and some crossbred Merino in Australia, suggesting that birthcoat score could add useful information as selection criteria to improve lamb survival (Brien et al., 2010). A high positive genetic correlation between birthcoat type and cold resistance was observed in newborn Merino lambs (Slee et al., 1991). Results of the present study clearly demonstrated the importance of birthcoat type for lamb survival. Thus, any selection to obtain a hairy coat at birth, which is a highly heritable trait, will result in a stronger aptitude for lambs to survive. Rapid progress could be easily obtained, whether or not the variability of birthcoat is under the control of a few major genes, as birthcoat type can be easily scored at birth. Results of the present study clearly demonstrated the importance of birthcoat type for lamb survival and gave important information about the essential role of a long-hairy birthcoat and its positive consequences on survival rate, heat body loss, and growing performance. Considerations about any disadvantage of a long-hairy birthcoat on fleece quality in the adult and therefore its commercial value can be easily avoided. Within European sheep farming, the value of raw wool is very low and the income from wool is often less than shearing costs.
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Conclusion Under harsh environment and permanent exposure outdoors on rangelands, lambs bearing a hairy birthcoat are more adapted to survive, especially around lambing time, and show better growth performance, up to weaning, than lambs bearing a fine and short-woolly coat. The birthcoat plays an essential role concerning heat body loss. Consequently, structure and composition of the birthcoat have to be considered in any genetic strategy for sheep meat production under harsh environmental conditions. The choice of a well-adapted breed or crossbred animals remains a key question. A selection program aiming at increasing coat hairiness at birth has to be developed and could be easily achieved through any classical phenotypic selection, as birthcoat type is a strongly heritable trait that can be easily scored at birth. LITERATURE CITED Alexander, G. 1958. Heat production of newborn lambs in relation to type of birthcoat. Proc. Aust. Soc. Anim. Prod. 2:10–14. Allain, D., D. Foulquié, D. François, P. Autran, B. Bibé, and J. Bouix. 2009. The birthcoat type: An important component of lamb survival in the French Romane breed raised under permanent exposure outdoors. In: Book of abstracts. 60th Annu. Meet. EAAP, Barcelona, Spain. Abstract 257. Allain, D., I. Lantier, J. M. Elsen, D. François, J. C. Brunel, J. L. Weisbecker, L. Schibler, D. Vaiman, E. P. Cribiu, A. Gautier, P. Berthon, and F. Lantier. 1998. A design aiming at detecting QTL controlling wool traits and other traits in the Inra401 sheep line. In: Proc. 6th World Cong. Genet. Appl. Livest. Prod., Armidale, NSW Australia. 24:51–54. Allain, D., L. Schibler, L. Mura, F. Barillet, T. Sechi, R. Rupp, S. Casu, E. P. Cribiu, and A. Carta. 2006. QTL detection with DNA markers for wool traits in a sheep backcross Sarda × Lacaune resource population. In: Proc. 8th World Cong. Genet. Appl. Livest. Prod., Belo Horizonte, MG, Brazil. Communication No. 05–07. Bouix, J., M. Jacquin, D. Foulquié, P. Autran, P. Guillouet, D. Hubert, and B. Bibe. 2002. Genetic effects on sheep production in harsh environment and extensive management system. In: Proc. 7th World Cong. Genet. Appl. Livest. Prod., Montpellier, France. 29:441–444. (Communication No. 02–02) Brien, F. D., M. L. Hebart, D. H. Smith, J. E. Hocking Edwards, J. C. Greef , K. W. Hart, G. Refshauge, T. L. Birt-Gardiner, G. Gaunt, R. Behrendt, M. W. Robertson, G. N. Hinch, K. G. Geenty, and J. H. J. van der Werf. 2010. Opportunities for genetic improvement of lamb survival. Anim. Prod. Sci. 50:1017–1050. Cloete, S. W. P., I. Misztal, and J. J. Olivier. 2009. Genetic parameters and trends for lamb survival and birth weight in a Merino flock divergently selected for multiple rearing ability. J. Anim. Sci. 87(7):21962–208. Dry, F. W. 1956. Twenty-five years of Mendelian sheep breeding. Proc. N. Z. Soc. Anim. Prod. 16:130–140. Dry, F. W. 1958. Further breeding experiments with New Zealand Romney N-type sheep to 1956. Aust. J. Agric. Res. 9:348–360. Gilmour, A. R., B. J. Gogel, B. R. Cullis, and R. Thompson, 2009. ASREML User guide manual. Release 3.0. Orange 2800 Australia, NSW Agriculture. Gregory, I. P. 1982. Genetic studies of South Australian Merino sheep. III Heritabilities of various wool and body traits. Aust. J. Agric. Res. 33:355–362.
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