Several studies have evaluated the effects of the dietary application of exogenous alpha-amylase preparations (AMA) as a strategy to increase total tract starch digestibility (TTSD) and milk yield (MY) in dairy cows, but the results have been inconsistent. Thus, the objective of this study was to evaluate the effects of the dietary application of AMA on the performance, digestibility, and rumen fermentation of lactating dairy cows using a meta-analytic method. A total of 18 peer-reviewed manuscripts (N = 32 treatment comparisons) from 2003 to 2019 were systematically identified following the PRISMA method. The weighted raw mean differences between dietary AMA and control treatments were compared with a robust variance estimation. Likewise, diet characteristics like crude protein (CP) content, NDF content, starch content, days in milk (DIM), experimental design (Latin square and continuous), and AMA dose (0 to 732 Kilo Novo units (KNU)/ kg TMR) were used as covariates in a meta-regression, subgrouping, and dose-response analysis. Compared to the control, dietary AMA increased (P < 0.05) DM digestibility (69.32 vs. 68.30%), TTSD (94.62 vs. 94.10%), milk protein concentration and yield (3.11 vs. 3.08 %; 1.14 vs. 1.10 kg/d) and tended to increase (P = 0.09) fat-corrected milk (35.96 vs. 35.10 kg/d) but no effects were observed on DM intake (22.99 vs. 22.90 kg/d) and feed efficiency (1.50 vs. 1.48). Dietary AMA tended (P = 0.10) to reduce rumen pH (6.27 vs 6.30). Both, the enzyme dose, and DIM strongly influenced (P < 0.05) the effects of AMA on digestibility and performance. The dose-response analysis revealed that feeding 600 KNU/kg to high-producing early lactation (< 70 DIM) dairy cows increased FCM and milk protein. Accounting for the type of experimental design was associated with a lower between-studies-variance among comparisons. Overall, this meta-analysis supports the hypothesis that dietary AMA supplementation is associated with a better lactational performance in dairy cows. However, these effects are only suitable for high-producing early lactation dairy cows.

中文翻译：

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日粮中应用外源α-淀粉酶制剂对泌乳奶牛生产性能、营养物质消化率和瘤胃发酵影响的荟萃分析


多项研究评估了在日粮中应用外源 α-淀粉酶制剂 (AMA) 作为提高奶牛总消化道淀粉消化率 (TTSD) 和产奶量 (MY) 的策略的效果，但结果并不一致。因此，本研究的目的是使用荟萃分析方法评估日粮中应用 AMA 对泌乳奶牛生产性能、消化率和瘤胃发酵的影响。根据 PRISMA 方法，系统地鉴定了 2003 年至 2019 年期间总共 18 份同行评审的手稿（N = 32 项治疗比较）。将膳食 AMA 和对照治疗之间的加权原始平均差异与稳健的方差估计进行比较。同样，饮食特征，如粗蛋白 (CP) 含量、NDF 含量、淀粉含量、奶中天数 (DIM)、实验设计（拉丁方和连续）和 AMA 剂量（0 至 732 千克新单位 (KNU)/kg TMR） ）被用作荟萃回归、分组和剂量反应分析中的协变量。与对照相比，日粮 AMA 增加 (P < 0.05) DM 消化率（69.32 vs. 68.30%）、TTSD（94.62 vs. 94.10%）、乳蛋白浓度和产量（3.11 vs. 3.08 %；1.14 vs. 1.10 kg） /d）并且倾向于增加（P = 0.09）脂肪校正牛奶（35.96 vs. 35.10 kg/d），但没有观察到对干物质摄入量（22.99 vs. 22.90 kg/d）和饲料效率（1.50 vs. 1.48）的影响）。日粮 AMA 倾向于降低瘤胃 pH 值（P = 0.10）（6.27 vs 6.30）。酶剂量和 DIM 都强烈影响 (P < 0.05) AMA 对消化率和性能的影响。剂量反应分析显示，给高产早期泌乳 (< 70 DIM) 奶牛饲喂 600 KNU/kg 会增加 FCM 和乳蛋白。 考虑到实验设计的类型与比较中较低的研究间方差相关。总体而言，这项荟萃分析支持这样的假设：日粮中补充 AMA 与奶牛更好的泌乳性能相关。但这些效果仅适用于高产早期泌乳奶牛。