不同生理阶段犊牛赖、蛋、苏氨酸平衡模式研究

应用部分扣除饲粮氨基酸(AA)的氮平衡试验法研究了中国荷斯坦犊牛不同生理阶段(2～3周龄和5～6周龄)赖(Lys)、蛋(Met)、苏氨酸(Thr)平衡模式。每个阶段各用12头犊牛进行N平衡试验。每个N平衡试验均设4个处理组,即氨基酸相对平衡的代乳品(PC)组(赖氨酸、蛋氨酸、苏氨酸含量依次为2.34%、0.72%、1.80%)、在PC基础上轮流将赖、蛋、苏氨酸扣除30%的其它3种代乳品(分别为PC-Lys、PC-Met、PC-Thr)组。每个处理设3个重复,每个重复1头牛。所有代乳品等能(17.8MJ/kg)等蛋白(22%)。试验结果表明,按单位代谢体重的N沉积与氨基酸摄入量计算,中国荷斯坦犊牛2～3周龄日粮模式为代乳品时,Lys、Met、Thr的平衡比例100:29:70;5～6周龄日粮模式为代乳品、开食料和羊草时,平衡比例为100:30:60;两阶段3种氨基酸的限制性顺序均为Lys、Met、Thr。

The proper ratio of lysine,methionine and threonine for calves from 0 to 2 months of age

Two nitrogen balance trials by partial deduction of amino acids (AA) of a milk replacer (MR) were conducted to investigate the proper ratio of lysine (Lys),methionine (Met) and threonine (Thr) for calves during 2～3 and 5～6 w of age. Twelve newborn Holstein calves were randomly assigned to one of 4 treatments:a milk replacer with a well balanced AAs containing 2.34% Lys,0.72% Met and 1.80% Thr (positive control,PC),or the same milk replacer with either Lys,Met or Thr reduced by 30%,respectively (PC-Lys,PC-Met and PC-Thr treatments). All the MRs were isocaloric (17.8 MJ/kg) and isonitrogenous (22% crude protein). The results showed that,based on N retention and N intake per kg metabolic weight in calves,the limiting sequence of the 3 AAs was ranked as Lys,Met and Thr,and the proper ratios of the 3 AAs for 2-3 and 5-6 wk of age of calves were found to be 100:29:70 and 100:30:60,respectively.