Stanton T L, Jones L R, Everett R W, Kachman S D
Department of Animal Science, Cornell University, Ithaca, NY 14853-4801.
J Dairy Sci. 1992 Jun;75(6):1691-700. doi: 10.3168/jds.S0022-0302(92)77926-0.
Test day models were used to estimate lactation curves for milk, fat, protein, fat percentage, and protein percentage and to study the influence of age, season, and herd productivity on Holstein lactation curves. Random effects of lactation within herd and fixed effects of herd test date were absorbed. Fixed effects of cow's age on test day and either DIM (57 divisions) by parity (1, 2, greater than or equal to 3) class or season of calving (winter or summer) by DIM by parity class were estimated. Lactation curves for yield traits derived from DIM solutions were flatter for first versus later lactation, even without addition of age effects. Differences between lactation curves for the two seasons were slight, suggesting that most observed seasonal differences are caused by seasonal productivity accounted for by herd test date effects. At peak, winter calving cows yielded slightly more milk of similar fat percentage but of lower protein percentage than those calving in summer. Data were also partitioned into nine subsets based on rolling herd milk and fat percentage. Lactation curves for yield traits, but not percentage traits, varied with rolling herd milk. Lactation curves for fat yield and percentage varied with rolling herd fat percentage.
使用测试日模型来估计牛奶、脂肪、蛋白质、脂肪百分比和蛋白质百分比的泌乳曲线，并研究年龄、季节和牛群生产力对荷斯坦奶牛泌乳曲线的影响。吸收了牛群内泌乳的随机效应和牛群测试日期的固定效应。估计了奶牛测试日年龄的固定效应，以及按胎次（1、2、大于或等于3）分类的产犊间隔天数（DIM，57个区间）或按胎次分类的产犊季节（冬季或夏季）与DIM的固定效应。即使不考虑年龄效应，首次泌乳与后续泌乳相比，由DIM解决方案得出的产量性状泌乳曲线也更平缓。两个季节泌乳曲线之间的差异较小，这表明观察到的大多数季节性差异是由牛群测试日期效应所解释的季节性生产力导致的。在泌乳高峰期，冬季产犊的奶牛所产牛奶脂肪百分比相似，但蛋白质百分比低于夏季产犊的奶牛，且产奶量略高。数据还根据滚动牛群牛奶和脂肪百分比分为九个子集。产量性状的泌乳曲线（而非百分比性状）随滚动牛群牛奶而变化。脂肪产量和百分比的泌乳曲线随滚动牛群脂肪百分比而变化。
