摘要
Lowering the dietary protein content can reduce N excretions and NH3 emissions from manure and increase milk N efficiency of dairy cows. However, milk yield (MY) and composition can be compromised due to AA deficiency. Methionine and Lys are known as first limiting EAA for dairy cows, and recently His is also mentioned as limiting, especially in grass-based or low-protein diets. To examine this, a trial was conducted with a 3-wk pre-experimental adaptation period (diet 16.5% crude protein), followed by a depletion period of 4 wk, in which 39 cows (average ± standard deviation: 116 ± 29.3 d in milk, 1.8 ± 1.2 lactations, 638 ± 73.2 kg of body weight, and 32.7 ± 5.75 kg MY/d) received a low-protein diet (CTRL) (14.5% crude protein). Then, taking into account parity, His plasma concentration, and MY, cows were randomly assigned to 1 of 3 treatment groups during the rumen-protected (RP) AA period of 7 wk; (1) CTRL; (2) CTRL + RP-Met + RP-Lys (MetLys); (3) CTRL + RP-Met + RP-Lys + RP-His (MetLysHis). Products were dosed, assuming requirements for digestible (d) Met, dLys, and dHis being, respectively, 2.4%, 7.0%, and 2.4% of intestinal digestible protein. In the cross-back period of 5 wk, all cows received the CTRL diet. During the last week of each period, a N balance was conducted by collecting total urine and spot samples of feces. Total feces production was calculated using the inert marker TiO2. Statistical analysis was performed with a linear mixed model with cow as random effect and data of the last week of the pre-experimental period used as covariate for the animal performance variables. No effect of supplementing RP-Met and RP-Lys nor RP-Met, RP-Lys, and RP-His on feed intake, milk performance, or milk N efficiency was observed. However, the plasma AA profile indicated additional supply of dMet, dLys, and dHis. Nevertheless, evaluation of the AA uptake relative to the cow's requirements showed that most EAA (exclusive Arg and Thr) were limiting over the whole experiment. Only dHis was sufficiently supplemented during the RP-AA period due to an overestimation of the diet's dMet and dLys supply in the beginning of the trial. The numerically increased milk urea N and urinary N excretion when RP-Met, RP-Lys, and RP-His were added to the low-protein diet suggest an increased catabolism of the excess His.
摘要译文
降低饮食蛋白质含量可以减少氮的排泄物和NH 3的粪便排放，并提高奶牛的牛奶n效率。但是，由于AA缺乏，牛奶产量（我的）和成分可能会损害。蛋氨酸和LYS被称为乳制奶牛的第一个限制EAA，最近他也被称为限制，尤其是在草基或低蛋白质饮食中。为此，进行了一项试验，当时是3周的实验前适应周期（饮食16.5％粗蛋白），其次是4周的耗竭周期，其中39头母牛（平均±标准偏差：116±29.3 d in牛奶，1.8±1.2泌乳，体重638±73.2公斤，32.7±5.75 kg MY/D）接受了低蛋白饮食（CTRL）（14.5％粗蛋白）。然后，考虑到平等，他的血浆浓度和我的奶牛在受瘤胃保护（RP）的AA期间为7周期间被随机分配给3个治疗组中的1个；（1）Ctrl;（2）CTRL + RP-MET + RP-LYS（Metlys）;（3）CTRL + RP-MET + RP-LYS + RP-HIS（MetlyShis）。对产物进行了加工，假设对可消化（D）Met，Dlys和Dhis的要求分别为2.4％，7.0％和2.4％的肠道消化蛋白。在5周的跨回后期，所有母牛都接受了CTRL饮食。在每个时期的最后一周，通过收集尿液和粪便样本来实现N平衡。使用惰性标记TIO 2计算总粪便产生。用带有牛的线性混合模型作为随机效应和实验前的最后一周的数据进行统计分析，作为动物性能变量的协变量。没有观察到补充RP-MET和RP-lys或RP-MET，RP-LYS和RP-HIS对饲料摄入，牛奶性能或牛奶N效率的影响。但是，血浆AA曲线表明额外的DMET，DLYS和DHIS供应。然而，相对于牛的要求，对AA吸收的评估表明，大多数EAA（独家ARG和THR）在整个实验中都在限制。由于在试验开始时对饮食的dmet和dlys供应高估，在RP-AA期间只能充分补充DHI。当将RP-MET，RP-lys和RP-HIS添加到低蛋白质饮食中时，数值增加的牛奶尿素和尿液排泄表明对他的过剩的分解代谢增加。
T. Van den Bossche; K. Goossens; B. Ampe; G. Haesaert; ... L. Vandaele. Effect of supplementing rumen-protected methionine, lysine, and histidine to low-protein diets on the performance and nitrogen balance of dairy cows[J]. Journal of Dairy Science, 2023,106(3): 1790-1802