The objective of this study was to estimate cow variability that can be used to determine the optimal sample size for digestibility trials using lactating dairy cows. Experimental design was randomized complete block design having three blocks and three dietary treatments. Three similarly managed nearby intensive farms were considered as blocks, and three diets were formulated to have 0.7, 1.0, and 1.3 neutral detergent fiber (NDF): starch ratio. In each farm, 18 cows were assigned for each dietary treatment and five sample sizes per each treatment group were simulated by simple random sampling of data from18,15, 12, 9 and 6 cows respectively. Intake was not affected by diet or sample size (p > 0.05). Estimated cow variability (as standard deviation) for digestibility of dry matter, NDF and starch were 3.8 g/kg, 5.1 g/kg and 3.3 g/kg, respectively. A major implication of this study is that cow variability is greatest for NDF digestibility and the use of a minimum of 12 cows per dietary treatment is adequate to reliably detect treatment effects on the digestibility of NDF, starch and dry matter using cows fed in groups with randomized block design under these experimental conditions.

中文翻译：

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哺乳期饲喂以玉米为基础的日粮的奶牛营养消化中母牛之间的变异性估算。

这项研究的目的是评估奶牛的变异性，可以用来确定使用泌乳奶牛进行消化率试验的最佳样本量。实验设计是具有三个块和三个饮食处理的随机完整块设计。将附近三个管理类似的集约化养殖场视为街区，并配制了三种日粮，使其具有0.7、1.0和1.3的中性洗涤剂纤维（NDF）：淀粉比率。在每个农场中，每种饮食处理均分配了18头奶牛，并且通过分别从18、15、12、9和6头奶牛的简单随机采样数据模拟了每个处理组的五个样本量。摄入量不受饮食或样本量的影响（p> 0.05）。奶牛干物质，NDF和淀粉消化率的估计变异性（作为标准偏差）分别为3.8 g / kg，5.1 g / kg和3.3 g / kg。这项研究的主要意义在于，奶牛的变异性最大，对NDF的消化率具有影响，并且在每个日粮处理中至少使用12头奶牛足以可靠地检测出使用高脂奶牛喂养的奶牛对NDF，淀粉和干物质消化率的治疗效果。在这些实验条件下进行随机区组设计。