Nitrogen Metabolism of Lactating Ewes Fed Rumen-Protected Methionine and Lysine G. P. LYNCH,1 T. H. ELSASSER,1 C. JACKSON, JR.,1 T. S. RUMSEY,1 and M. J. CAMp2 United States Department of Agriculture Beltsville. MD 20705 ABSTRACT

Abbreviation key: BCAA = branched-chain amino acid, HBA = 3-hydroxybutyrate, LP = low protein, LPAA = low protein supplemented with amino acids, Lys = lysine, Met = methionine, MP = moderate protein, MPAA = moderate protein supplemented with amino acids.

Twenty multiparous, crossbred, blackfaced ewes and their newborn twin lambs were assigned to one of four dietary treatments in a 2 x 2 factorial experiment to examine the effects of increased supply of CP or a mixture of encapsulated methionine and lysine or both on the performance of ewes and their nursing twin lambs. Ewes were fed ad libitum amounts of either a 10.2% low CP diet or a 16.2% moderate CP diet with or without additional encapsulated amino acids. Nitrogen metabolism trials were conducted simultaneously on both ewes and lambs at wk 2, 4, and 8 of lactation. Analyses were conducted for blood urea N, plasma 3-hydroxybutyrate, lactate, NEFA, insulin, and amino acids (plasma, feed, and milk). Ewe DMI, BW, BW gain, and milk yield were not changed by dietary treatments. Balance of N and N digested were increased by moderate CP treatment. The portion of retained N used for milk synthesis was increased by low CP treatment. Methionine and total branched-chain amino acids were increased by encapsulated amino acids and by protein treatment. Gains in BW and N balance were increased in lambs nursing ewes fed protected amino acids. Increased growth of nursing lambs would be an important beneficial effect of supplementing diets of ewes with encapsulated methionine and lysine. (Key words: sheep, N balance, amino acids, lamb growth)

INTRODUCTION

Received July 30, 1990. Accepted December 5, 1990. lRuminant Nutrition Laboratory, Livestock and Poultry Sciences Institute, Beltsville, MD 20705. 2Statistical Consulting Analysis Service, ARS, Beltsville, MD 20705. 1991 J Dairy Sci 74:2268-2276

Encapsulation of specific amino acids is one technique available for protecting them from bacterial deamination in the romen so they are available for absorption in the small intestine (1). This technique may be of value for improving the protein metabolism of lactating ewes as well as lactating dairy cows. Methionine (Met) is considered the first-limiting amino acid for milk protein synthesis (6,7, 10, 22, 27), and lysine (Lys) may be a colimiting amino acid (3, 7, 26). Additional studies with lactating dairy cows have shown that rumenprotected Met was effective in delivering Met postruminally, which resulted in an increased Met concentration in plasma (18, 19). Work with lambs has shown that Lys may be the first-limiting amino acid in purified diets supplemented with zein (9). Methionine and Lys may be the frrst- and second-limiting amino acids in microbial protein (27), and Met, Lys, and threonine may be limiting in microbial protein when urea is the only supplemental N source (16, 17). The abomasal infusion of DL-methionine into wethers fed 11.6 and 14.1 % CP diets increased N retention (25). The purpose of this experiment was to utilize dietary encapsulated Met and Lys as a method to improve the specific amino acid supply of lactating ewes and to determine its effects on milk production and growth of their twin lambs. MATERIALS AND METHODS

Twenty multiparous, crossbred, blackfaced ewes (64 kg mean initial BW) and their re-

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NITROGEN METABOLISM OF LACTATING EWES

TABLE 1. Composition of moderate CP and low CP diets fed to lactating ewes and the creep diet fed to their lambs. Diets Moderate! protein

Item

Low! protein

ereep2

(%, as fed) Ingredients Ground com Finely ground com Gtound barley Finely ground barley Soybean meal Finely ground soybean meal Skim milk powder White lard Molasses Orchardgrass hay Wheat straw Alfalfa hay Mineral mix3 Limestone Aureomycin 10 Composition CP, %4

ME,M~

26.7

37.3

0 32.4

24.0

21.3

10.7

2.7 0 0 0 5.3 8.0 24.0 0 .6 .8 0

19.9 10.0 5.0 0 0 0 .4 1.5 .8 .1

10.18 2.32

18.92 2.36

29.9

0 0 0 5.3 32.0 0 0

.6 .6 0 16.27 2.41

0

IGtound through a 1.9-mm screen, the bay and grain were mixed to make a complete diet. Orchardgrass bay was flIst-eutting. 2 Gtound through a 1.9-mm screen, the bay and grain were mixed to make a complete creep diet. Alfalfa bay was third-cutting, l/4 bloom. 3Commercial mineral mix containing 14.0 to 16.0% salt; 23.5 to 28.0% Ca; 6.60% P (minimum); 1.5% Mg (minimum); .25% Zn (minimum); .007% I (minimum); vitamin A, 770,000 USP/kg (minimum); vitamin D, 55,000 USPI kg; vitamin E, 220 IUIkg; vitamin B12' .022 mgIkg and also containing undisclosed amounts of mineral oil, flavors, and sodium selenite. 4Analytically measured. SCalculated from Atlas Washington, DC.

of Nutritional Data on U. S. and Canadian Feeds, 1971, National Academy of Sciences,

spective twin lambs were assigned to one of four dietary treatments within 5 d after parturition. The lambs were sired by either a pmebred Hampshire or Suffolk ram. A completely randomized design with a 2 x 2 factorial arrangement of treatments was employed in which 10 ewes were individually fed a totally mixed, 10.2% low CP (LP) diet and 10 ewes were fed a 16.2% moderate CP (MP) diet. Within each protein-level diet, half of the ewes were supplemented with .28% encapsulated Lys plus .11 % encapsulated Met. These amino acidsupplemented LP and MP diets are designated as LPAA and MPAA, respectively. The encapsulated Lys contained 1.3% active Lys, and the encapsulated Met contained 1.1 % active Met (Eastman Kodak, Kingsport, TN). The ewes were given ad libitum access to their

respective diets during the entire experiment, and the lambs had ad libitum access to a creep diet. The feed ingredient composition of the ewe and lamb diets appears in Table 1, and the amino acid composition of the ewe diets appears in Table 2. Separate N metabolism trials were conducted simultaneously on both ewes and their twin lambs at wk 2, 4, and 8 of lactation in double metabolism crates that held a ewe in one side and the twin lambs in the adjoining side. Estimates of ewe milk production were made at 4-h intervals during each day of the balance period by the weigh-suckle-weigh method as described by Lynch et al. (13). Analysis of weekly samples representing each balance period were for CP content of feed, feces, urine, and milk. Analysis of plasma J01l1'I1a1 of DaiIy Science Vol. 74, No.7, 1991

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LYNCH ET AL.

TABLE 2. Amino acid composition of moderate protein (MP) and low protein (lP) diets supplemented with protected amino acids (MPAA or LPAA). Diets Item

MP

MPAA

LP

LPAA

(g/100 g DM) Methionine Lysine Cystine Threonine Arginine Valine Proline Leucine Isoleucine Aspartic Glutamic Alanine Serine Ammonia

.28 .77 .30 .68 1.00 .88 1.12 1.49 .67 1.62 2.78 .95 .77 .43

samples taken from ewes during each balance period were for blood urea N, a metabolic profile (Metpath Inc., Rockville, MD), 3-hydroxybutyrate (HBA), plasma amino acids, lactate, and insulin according to previously described methods (13). The quantitative determination of serum NEFA was by the use of an in vitro enzymatic, colorimetric test kit (Wako Pure Chemical Industries, Ltd., Dallas, TX). The general linear models repeated measures procedure was used to allow for the within-animal correlation between measurements over time. The variation due to main effects, protein level, protected amino acids, and their interactions was tested. Individual animal variation within protein level and amino acid treatment was used as the error term. Linear and quadratic effects with time of lactation along with interactions of protein level and amino acids were estimated by orthogonal comparisons (24). Differences were significant at P < .01 unless otherwise noted. RESULTS AND DISCUSSION

It was not possible to balance the twin lambs exactly by sex in the four dietary treatments at the onset of the experiment An initial analysis of the data by dietary treatments showed that there were no signifkant differences due to sex of the lamb; therefore, sex of Journal of Dairy Science Vol. 74, No.7, 1991

.39 .87 .30 .67 .97 .86 1.13 1.46 .67 1.57 2.67 .94 .74 .43

.19 .43 .22 .41 .53 .52 .77 1.01 .38 .86 1.87 .63 .49 .28

.32 .51 .21 .41 .55 .54

.84 1.05 .40 .88 1.88 .66 .50 .29

lamb was dropped from the model, and the four diets were analyzed jointly. Means of DMI, BW, and BW gain of ewes were not changed by protein or amino acid treatments, but DMI, BW, and BW gain (P < .04) were increased linearly and quadratically, respectively, with time through lactation (fable 3). Intake of N by ewes was increased by protein treatment (84.0 g/d MP; 54.6 g/d LP) as a result of experimental protocol. At these intakes, the MP diet supplied 125% and the LP diet supplied 81 % of the NRC (15) suggested daily requirements for lactating ewes nursing twin lambs. All ewes gained BW throughout lactation, but the ewes fed LP had the lowest and ewes fed LPAA had the highest daily gains (fable 3). Intake of N by ewes increased quadratically with time through lactation. Protein but not amino acid treatment increased N balance (19.4 g/d MP; 8.9 g/d LP). Nitrogen digested was increased by protein treatment (65.3% MP; 55.1% LP), but N retention was not Both N retention (P < .03) and N digested were increased quadratically with time through lactation. Previous work has shown that N digestibility but not N retention was increased linearly in growing lambs fed increasing amounts of encapsulated Met (14). In these lactating ewes, increased dietary protein was more beneficial for their protein metabolism than were the encapsulated amino acids.

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TABLE 3. Means for BW, feed intakes, measures of N metabolism, millt yield, the portion of retained N used for millt synthesis (NRMS), blood urea N, hematocrit, IJ-hydroxybutyrate (HBA), glucose, lactate, insulin, triglycerides, and NEFA in ewes by dietary treatment l and by orthogonal comparison. 2 Effects

Diets Item

MP

MPAA

LP

LPAA

SEM

DMI, kg/d Ewe BW, kg Ewe BW gain, gld N Intake, gld Methionine intake, gld Lysine intake, gld N Balance, gld N Digested, % N Retained, % Milk yield, kgld NRMS, % Blood urea N, mgldl Hematocrit, % HBA, J.IM/dl Glucose, mgldl Lactate, roM Insulin, ng{m1 Triglycerides, mg/dl NEFA, mgldl

3.10 65.4 170. 83.4 8.68 23.87 21.2 66.3 47.1 1.9 46.0 20.7 28.0 .49 72.3 1.77 1.32 28.8 306.0

3.20 67.1 164. 84.6 12.48 27.84 17.6 64.3 45.7 2.20 55.3 17.3 26.1 .46 73.6 1.78

2.97 69.5 134. 50.0 5.64 12.77 6.5 52.7 42.8 1.78 75.5 6.5 27.6 .28 72.1 1.76 .82 27.2 250.4

3.34 69.9 202. 59.2 10.69 17.03 11.2 57.5 45.5 1.76 72.7 7.5 23.7 .45 75.0 1.43 .84 27.4 221.8

.18 4.6 13.0

.99 23.1 471.0

P

AA

P x AA

- - - - (P

Nitrogen metabolism of lactating ewes fed rumen-protected methionine and lysine.

Twenty multiparous, crossbred, black-faced ewes and their newborn twin lambs were assigned to one of four dietary treatments in a 2 x 2 factorial expe...
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