Scibus, PO Box 660, Camden 2570, New South Wales, Australia.
Paradox Nutrition LLC, West Chazy, NY 12992.
J Dairy Sci. 2018 Jan;101(1):340-364. doi: 10.3168/jds.2016-12493. Epub 2017 Nov 8.
Meta-analytic methods were used to determine statistical relationships between metabolizable AA supplies and milk protein yield, milk protein percentage, and milk yield in lactating dairy cows. Sixty-three research publications (258 treatment means) were identified through a search of published literature using 3 search engines and met the criteria for inclusion in this meta-analysis. The Cornell Net Carbohydrate and Protein System (CNCPS) version 6.5 was used to determine dietary nutrient parameters including metabolizable AA. Two approaches were used to analyze the data. First, mixed models were fitted to determine whether explanatory variables predicted responses. Each mixed model contained a global intercept, a random intercept for each experiment, and data were weighted by the inverse of the SEM squared. The second analysis approach used classical effect size meta-analytical evaluation of responses to treatment weighted by the inverse of the treatment variance and with a random effect of treatment nested within experiment. Regardless of the analytical approach, CNCPS-predicted metabolizable Met (g/d) was associated with milk protein percentage and yield. Milk yield was positively associated with CNCPS-predicted metabolizable His, Leu, Trp, Thr, and nonessential AA (g/d). Milk true protein yield was also associated with CNCPS-predicted metabolizable Leu (g/d). Predicted metabolizable Lysine (g/d) did not increase responses in production outcomes. However, mean metabolizable Lys supply was less than typically recommended and the change with treatment was minimal (157 vs. 162 g; 6.36 vs. 6.38% metabolizable protein). Experiments based solely on Lys or Met interventions were excluded from the study database. It is possible that the inclusion of these experiments may have provided additional insight into the effect of these AA on responses. This meta-analysis supports other research indicating a positive effect of Met and His as co-limiting AA in dairy cows and suggests Leu, Trp, and Thr be given greater consideration in future research.
采用荟萃分析方法确定了泌乳奶牛可代谢氨基酸供应与乳蛋白产量、乳蛋白百分率和乳产量之间的统计关系。通过使用 3 个搜索引擎对已发表文献进行搜索，确定了 63 篇研究出版物（258 个处理平均值），这些出版物符合本荟萃分析的纳入标准。使用康奈尔净碳水化合物和蛋白质系统（CNCPS）版本 6.5 确定了包括可代谢氨基酸在内的饮食营养参数。采用两种方法分析数据。首先，拟合混合模型以确定解释变量是否可以预测响应。每个混合模型包含一个全局截距、每个实验的随机截距，数据权重为 SEM 平方的倒数。第二种分析方法采用经典的效果大小荟萃分析，根据处理方差的倒数对处理响应进行加权，并用实验内嵌套的处理随机效应。无论采用哪种分析方法，CNCPS 预测的可代谢 Met（g/d）与乳蛋白百分率和产量相关。乳产量与 CNCPS 预测的可代谢 His、Leu、Trp、Thr 和非必需氨基酸（g/d）呈正相关。乳真蛋白产量也与 CNCPS 预测的可代谢 Leu（g/d）相关。预测的可代谢 Lys（g/d）不会增加生产结果的反应。然而，赖氨酸的平均可代谢供应低于通常建议的水平，且处理变化最小（157 比 162 g；6.36 比 6.38%可代谢蛋白）。本研究数据库排除了仅基于 Lys 或 Met 干预的实验。这些实验的纳入可能为这些氨基酸对反应的影响提供了更多的见解。本荟萃分析支持其他研究，表明 Met 和 His 作为奶牛的共限制氨基酸具有积极作用，并表明 Leu、Trp 和 Thr 在未来的研究中应给予更多考虑。
