Hussein A H, Batista E D, Miesner M D, Titgemeyer E C
J Anim Sci. 2016 Feb;94(2):656-64. doi: 10.2527/jas.2015-9717.
Six ruminally cannulated Holstein steers (202 ± 15 kg) were used to study the effects of ruminal ammonia loading on whole-body lysine (Lys) utilization. Steers were housed in metabolism crates and used in a 6 × 6 Latin square design. All steers received 2.52 kg DM/d of a diet (10.1% CP) containing 82% soybean hulls, 8% wheat straw, 5% cane molasses, and 5% vitamins and minerals, and 10 g/d of urea (considered to be part of the basal diet) was ruminally infused continuously to ensure adequate ruminal ammonia concentrations. All steers were ruminally infused continuously with 200 g/d of acetic acid, 200 g/d of propionic acid, and 50 g/d of butyric acid and abomasally infused with 300 g/d of glucose continuously to increase energy supply without increasing microbial protein supply. Steers were also abomasally infused continuously with an excess of all essential AA except Lys to ensure that Lys was the only limiting AA. Treatments were arranged as a 3 × 2 factorial with 3 levels of urea (0, 40, or 80 g/d) continuously infused ruminally to induce ammonia loading and 2 levels of Lys (0 or 6 g/d) continuously infused abomasally. Treatments did not affect fecal N output ( = 0.37). Lysine supplementation decreased ( < 0.01) urinary N excretion from 51.9 g/d to 44.3 g/d, increased ( < 0.01) retained N from 24.8 to 33.8 g/d, increased ( < 0.01) plasma Lys, and decreased ( ≤ 0.05) plasma serine, tyrosine, valine, leucine, and phenylalanine. Lysine supplementation also tended ( = 0.09) to reduce plasma urea-N. Urea infusions linearly increased ( = 0.05) retained N (27.1, 29.3, and 31.5 g/d) and also linearly increased ( < 0.01) urinary N excretion (31.8, 48.1, and 64.4 g/d), urinary urea (21.9, 37.7, and 54.3 g/d), urinary ammonia (1.1, 1.4, and 1.9 g/d), and plasma urea (2.7, 4.0, and 5.1 mM), and linearly decreased plasma alanine ( = 0.04) and plasma glycine ( < 0.01). Assuming that retained protein is 6.25 × retained N and contains 6.4% Lys, the incremental efficiencies of infused Lys utilization were 51%, 59%, and 69% for steers receiving 0, 40, and 80 g/d of urea, respectively, indicating that ruminal ammonia loads may improve the efficiency of Lys utilization. This is supported by observed increases in whole body-protein deposition in response to ammonia loading of our steers that were, by design, Lys deficient.
选用6头安装有瘤胃瘘管的荷斯坦公牛（体重202±15千克），研究瘤胃氨负荷对全身赖氨酸（Lys）利用率的影响。公牛饲养于代谢栏中，采用6×6拉丁方设计。所有公牛每日采食2.52千克干物质日粮（粗蛋白含量10.1%），日粮包含82%的大豆皮、8%的小麦秸秆、5%的甘蔗糖蜜以及5%的维生素和矿物质，并且通过瘤胃持续灌注10克/天的尿素（视为基础日粮的一部分）以确保瘤胃中有足够的氨浓度。所有公牛通过瘤胃持续灌注200克/天的乙酸、200克/天的丙酸和50克/天的丁酸，并通过皱胃持续灌注300克/天的葡萄糖，以增加能量供应而不增加微生物蛋白供应。公牛还通过皱胃持续灌注除赖氨酸外的所有必需氨基酸，以确保赖氨酸是唯一的限制性氨基酸。试验处理按3×2析因设计，通过瘤胃持续灌注3个水平的尿素（0、40或80克/天）以诱导氨负荷，通过皱胃持续灌注2个水平的赖氨酸（0或6克/天）。试验处理对粪氮排出量无影响（P=0.37）。补充赖氨酸使尿氮排出量从51.9克/天降至44.3克/天（P<0.01），使留存氮从24.8克/天增至33.8克/天（P<0.01），使血浆赖氨酸增加（P<0.01），并使血浆丝氨酸、酪氨酸、缬氨酸、亮氨酸和苯丙氨酸减少（P≤0.05）。补充赖氨酸也有降低血浆尿素氮的趋势（P=0.09）。灌注尿素使留存氮呈线性增加（P=0.05）（分别为27.1、29.3和31.5克/天），也使尿氮排出量（分别为31.8、48.1和64.4克/天）、尿尿素（分别为21.9、37.7和54.3克/天）、尿氨（分别为1.1、1.4和1.9克/天）和血浆尿素（分别为2.7、4.0和5.1毫摩尔）呈线性增加（P<0.01），并使血浆丙氨酸（P=0.04）和血浆甘氨酸（P<0.01）呈线性减少。假设留存蛋白质为6.25×留存氮且含6.4%的赖氨酸，对于分别接受0、40和80克/天尿素的公牛，灌注赖氨酸的利用增效分别为51%、59%和69%，表明瘤胃氨负荷可能提高赖氨酸的利用效率。本试验中设计的赖氨酸缺乏的公牛，其全身蛋白质沉积因氨负荷而增加，这支持了上述结论。
