ABSTRACT The objective of the study was to estimate genetic parameters of efficiency of crude protein utilisation (ECPU) and its genetic correlation (r G) with other production traits across lactation in grazing dairy cows. Data were originated from 467 (2016–17 season) and 460 cows (2017–18 season) representing Holstein-Friesian (F), Jersey (J) and their crosses (F×J), from two New Zealand farms. The ratio between crude protein yield in milk and crude protein intake is defined as ECPU. (Co)variance components between ECPU and other traits were estimated using bivariate random regression models (RRM) that included fixed effects of herd-test-date, parity, calving date, proportion of F, and F×J heterosis, with random effects of animal additive genetic, and within-lactation permanent environment. Estimates of heritability (h2 ) of daily ECPU ranged from 0.02 to 0.41. Estimates of r G between daily ECPU and milk yield traits were strong and positive throughout lactation suggesting that selection for milk production traits improves ECPU of dairy cows. Daily r G between ECPU and mid-infrared predictions of milk urea (MU) concentration were mostly negative during lactation confirming that cows with high ECPU had genetically lower MU. Estimates of genetic relationships between ECPU and fertility traits are required to assess implications of including ECPU in breeding objective.

中文翻译：

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放牧奶牛不同泌乳期粗蛋白利用效率的遗传参数及其与生产性状的关系

摘要 本研究的目的是估计放牧奶牛整个泌乳期粗蛋白利用效率 (ECPU) 的遗传参数及其与其他生产性状的遗传相关性 (r G)。数据来自新西兰两个农场的 467 头（2016-17 季节）和 460 头奶牛（2017-18 季节），代表荷斯坦-弗里斯兰（F）、泽西（J）及其杂交（F×J）。牛奶中粗蛋白产量与粗蛋白摄入量之比定义为 ECPU。使用双变量随机回归模型 (RRM) 估计 ECPU 和其他性状之间的（协）方差分量，该模型包括畜群测试日期、胎次、产犊日期、F 比例和 F×J 杂种优势的固定效应，随机效应为动物加性遗传和泌乳期永久环境。每日 ECPU 的遗传力 (h2) 估计值介于 0.02 至 0.41 之间。日 ECPU 和产奶量性状之间的 r G 估计值在整个泌乳期很强且为正，表明对产奶性状的选择提高了奶牛的 ECPU。ECPU 和牛奶尿素 (MU) 浓度的中红外预测之间的每日 r G 在泌乳期间大多为负，证实具有高 ECPU 的奶牛具有较低的遗传性 MU。需要估计 ECPU 和生育性状之间的遗传关系，以评估将 ECPU 纳入育种目标的影响。ECPU 和牛奶尿素 (MU) 浓度的中红外预测之间的每日 r G 在泌乳期间大多为负，证实具有高 ECPU 的奶牛具有较低的遗传性 MU。需要估计 ECPU 和生育性状之间的遗传关系，以评估将 ECPU 纳入育种目标的影响。ECPU 和牛奶尿素 (MU) 浓度的中红外预测之间的每日 r G 在泌乳期间大多为负，证实具有高 ECPU 的奶牛具有较低的遗传性 MU。需要估计 ECPU 和生育性状之间的遗传关系，以评估将 ECPU 纳入育种目标的影响。