Lee C, Giallongo F, Hristov A N, Lapierre H, Cassidy T W, Heyler K S, Varga G A, Parys C
Department of Animal Science, Pennsylvania State University, University Park 16802.
Department of Animal Science, Pennsylvania State University, University Park 16802.
J Dairy Sci. 2015 Mar;98(3):1885-902. doi: 10.3168/jds.2014-8496. Epub 2014 Dec 26.
This study investigated the effect of metabolizable protein (MP) supply and rumen-protected (RP) Lys and Met supplementation on productivity, nutrient digestibility, urinary N losses, apparent total-tract digestibility of dietary AA, and the efficiency of AA utilization for milk protein synthesis in dairy cows. The experiment was conducted with 8 ruminally cannulated Holstein cows in a replicated 4×4 Latin square design trial with 21-d periods. Treatments were (1) MP-adequate diet (AMP; MP balance of -24 g/d); (2) MP-deficient diet (DMP; MP balance of -281 g/d); (3) DMP supplemented with 100 g of RPLys/cow per day (estimated digestible Lys supply=24 g/d; DMPL; MP balance of -305g/d); and (4) DMPL supplemented with 24 g of RPMet/cow per day (estimated digestible Met supply=15 g/d; DMPLM; MP balance of -256g/d). Diet had no effect on total-tract nutrient digestibility, milk production, and milk composition, but the DMP diets decreased urinary N excretion and the ammonia emitting potential of manure. Plasma Met concentration was increased by DMPLM compared with AMP. Supplementation with RPLys had no effect on plasma Lys. Concentration of most AA in milk protein was increased or tended to be increased by DMPLM compared with DMPL. Except for the AA supplemented as RPAA (i.e., Met and Lys), apparent total-tract digestibility of all dietary AA was generally greater for the DMP diets and ranged from 33% (Arg, AMP diet) to 67% (Thr, DMPL diet). Apparent recovery of dietary AA in milk protein followed the same trends, being greater for the DMP diets than AMP and generally lower for Lys and Met with the RPAA-supplemented diets versus AMP and DMP. The RPAA were apparently not used for milk protein synthesis in the conditions of this experiment. The AA recoveries in milk protein varied from around 17% (Ala) to 70% (Pro). Milk protein recoveries of essential AA (EAA) were around 54% for the DMP diet and 49% for AMP. The estimated efficiency of utilization of digestible EAA for milk protein synthesis was generally greater for the DMP diets compared with AMP. In this trial, blood plasma Lys and Met were labeled by abomasal pulse-dose of 15N-Lys and 13C-Met (respectively). Analysis of the 15N-Lys and 13C-Met decay curves in plasma indicated trends for a faster extraction of Lys and Met from plasma for the MP-deficient diets, compared with AMP. Overall, this study confirmed conclusions from previous analyses that the efficiency of utilization of dietary EAA will increase with decreasing MP-AA supply.
本研究调查了可代谢蛋白质（MP）供应以及瘤胃保护性（RP）赖氨酸和蛋氨酸补充对奶牛生产性能、养分消化率、尿氮损失、日粮氨基酸表观全肠道消化率以及氨基酸用于乳蛋白合成的利用效率的影响。试验采用8头安装了瘤胃瘘管的荷斯坦奶牛，进行重复4×4拉丁方设计试验，每期21天。处理方式包括：（1）MP充足日粮（AMP；MP平衡为-24克/天）；（2）MP缺乏日粮（DMP；MP平衡为-281克/天）；（3）DMP日粮每天每头奶牛补充100克RP赖氨酸（估计可消化赖氨酸供应量=24克/天；DMPL；MP平衡为-305克/天）；（4）DMPL日粮每天每头奶牛补充24克RPMet（估计可消化蛋氨酸供应量=15克/天；DMPLM；MP平衡为-256克/天）。日粮对全肠道养分消化率、产奶量和乳成分没有影响，但DMP日粮降低了尿氮排泄量和粪便的氨排放潜力。与AMP相比，DMPLM提高了血浆蛋氨酸浓度。补充RPLys对血浆赖氨酸没有影响。与DMPL相比，DMPLM使乳蛋白中大多数氨基酸的浓度增加或有增加趋势。除了作为RPAA补充的氨基酸（即蛋氨酸和赖氨酸）外，DMP日粮中所有日粮氨基酸的表观全肠道消化率通常更高，范围从33%（精氨酸，AMP日粮）到67%（苏氨酸，DMPL日粮）。日粮氨基酸在乳蛋白中的表观回收率也呈现相同趋势，DMP日粮高于AMP日粮，并且与AMP和DMP相比，补充RPAA的日粮中赖氨酸和蛋氨酸的回收率通常较低。在本试验条件下，RPAA显然未用于乳蛋白合成。乳蛋白中氨基酸的回收率从约17%（丙氨酸）到70%（脯氨酸）不等。DMP日粮中必需氨基酸（EAA）的乳蛋白回收率约为54%，AMP日粮为49%。与AMP相比，DMP日粮中可消化EAA用于乳蛋白合成的估计利用效率通常更高。在本试验中，通过在真胃脉冲注射15N-赖氨酸和13C-蛋氨酸（分别）对血浆赖氨酸和蛋氨酸进行标记。血浆中15N-赖氨酸和13C-蛋氨酸衰减曲线的分析表明，与AMP相比，MP缺乏日粮从血浆中提取赖氨酸和蛋氨酸的速度有加快的趋势。总体而言，本研究证实了先前分析得出的结论，即日粮EAA的利用效率将随着MP-AA供应的减少而提高。
