This study aimed to comprehensively evaluate the effects of glycerine supplementation at various concentrations on performance, rumen fermentation, blood metabolites and product characteristics of beef and dairy cattle in vivo by using a quantitative meta-analysis approach. Meta-analysis was performed by integrating a total of 52 studies from 39 articles and 182 treatments into a database. Data were constructed into an intact database and did not distinguish between beef and dairy cattle, except for the parameters of production performance and product characteristics. Data summarized were analysed by using a statistical meta-analysis that employed a fixed effect of glycerine supplementation level and a random effect of various studies for both beef and dairy cattle. Significance of an effect was stated at the probability level of p < .05, and p < .1 was considered as a tendency of significant. Results revealed that there was a linear decrease on dry matter intake (p < .01) and daily gain (p < .05) of beef cattle with the increasing levels of glycerine supplementation. Glycerine supplementation did not decrease milk production of lactating dairy cows. Molar proportion of acetate in the rumen was decreased (p < .001), whereas propionate and butyrate proportions were increased (both at p < .001) by glycerine supplementation. Generally, glycerine did not change nutrient digestibility except that it reduced fibre digestibility (p < .001). Glycerine supplementation linearly lowered triglyceride and NEFA concentrations (both at p < .05) in the blood serum, but not other blood metabolites. Glycerine tended to linearly increase (p < .1) carcass percentage in beef cattle. Increasing dietary glycerine levels decreased milk fat (p < .01) but elevated milk protein (p < .001). Glycerine tended to increase milk lactose (p < .1) by following a quadratic pattern. The proportion of MUFA was increased quadratically by glycerine supplementation (p < .05), whereas glycerine tended to decrease SFA by following a quadratic pattern (p < .1).

中文翻译：

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甘油作为肉牛和奶牛的饲料添加剂：性能、瘤胃发酵、血液代谢物和产品特性的荟萃分析

本研究旨在采用定量荟萃分析方法，综合评价添加不同浓度甘油对肉牛和奶牛体内性能、瘤胃发酵、血液代谢物和产品特性的影响。荟萃分析是通过将来自 39 篇文章和 182 种治疗的总共 52 项研究整合到数据库中来进行的。数据被构建到一个完整的数据库中，除了生产性能和产品特性的参数外，没有区分肉牛和奶牛。汇总的数据使用统计荟萃分析进行分析，该分析采用了甘油补充水平的固定效应和各种研究对肉牛和奶牛的随机效应。效应的显着性以概率水平表示p  < .05 和p  < .1 被认为是显着的趋势。结果表明， 随着甘油补充水平的增加，肉牛的干物质摄入量 ( p  < .01) 和日增重 ( p < .05)呈线性下降。补充甘油不会降低泌乳奶牛的产奶量。 通过补充甘油，瘤胃中乙酸的摩尔比例降低（p  < .001），而丙酸和丁酸的比例增加（均在p < .001）。一般来说，甘油不会改变营养物质的消化率，只是它降低了纤维的消化率（p < .001）。补充甘油会线性降低 血清中的甘油三酯和 NEFA 浓度（均p < .05），但不会降低其他血液代谢物。甘油倾向于线性增加 肉牛的胴体百分比( p < .1)。增加膳食甘油水平会降低乳脂 ( p  < .01)，但会增加乳蛋白 ( p  < .001)。甘油倾向于 按照二次模式增加牛奶乳糖 ( p < .1)。MUFA 的比例通过补充 甘油呈二次方增加 ( p < .05)，而甘油通过遵循二次方模式 ( p  < .1)倾向于降低 SFA 。