Despite its potential utility for predicting cows' milk yield responses to once-daily milking (ODM), the genetic basis of cow milk trait responses to ODM has been scarcely if ever described in the literature, especially for short ODM periods. This study set out to (1) estimate the genetic determinism of milk yield and composition during a 3-wk ODM period, (2) estimate the genetic determinism of milk yield responses (i.e., milk yield loss upon switching cows to ODM and milk yield recovery upon switching them back to twice-daily milking; TDM), and (3) seek predictors of milk yield responses to ODM, in particular using the first day of ODM. Our trial used 430 crossbred Holstein × Normande cows and comprised 3 successive periods: 1 wk of TDM (control), 3 wk of ODM, and 2 wk of TDM. Implementing ODM for 3 wk reduced milk yield by 27.5% on average, and after resuming TDM cows recovered on average 57% of the milk lost. Heritability estimates in the TDM control period and 3-wk ODM period were, respectively, 0.41 and 0.35 for milk yield, 0.66 and 0.61 for milk fat content, 0.60 and 0.80 for milk protein content, 0.66 and 0.36 for milk lactose content, and 0.20 and 0.15 for milk somatic cell score content. Milk yield and composition during 3-wk ODM and TDM periods were genetically close (within-trait genetic correlations between experimental periods all exceeding 0.80) but were genetically closer within the same milking frequency. Heritabilities of milk yield loss observed upon switching cows to ODM (0.39 and 0.34 for milk yield loss in kg/d and %, respectively) were moderate and similar to milk yield heritabilities. Milk yield recovery (kg/d) upon resuming TDM was a trait of high heritability (0.63). Because they are easy to measure, TDM milk yield and composition and milk yield responses on the first day of ODM were investigated as predictors of milk yield responses to a 3-wk ODM to easily detect animals that are well adapted to ODM. Twice-daily milking milk yield and composition were found to be partly genetically correlated with milk yield responses but not closely enough for practical application. With genetic correlations of 0.98 and 0.96 with 3-wk ODM milk yield losses (in kg/d and %, respectively), milk yield losses on the first day of ODM proved to be more accurate in predicting milk yield responses on longer term ODM than TDM milk yield.

尽管它有潜力用于预测每日一次挤奶（ODM）的牛奶产量反应，但是如果文献中很少描述，特别是对于短的ODM时期，牛奶对ODM的性状反应的遗传基础很少。这项研究旨在（1）估计三周ODM期间奶产量和组成的遗传确定性，（2）估算奶产量响应的遗传确定性（即，将奶牛转为ODM和奶产量后的奶产量损失）将其切换回每天两次挤奶后恢复； TDM），以及（3）寻求对ODM的产奶量响应的预测指标，尤其是在ODM的第一天。我们的试验使用了430头Holstein×Normande杂交母牛，包括3个连续的时期：1 wk TDM（对照），3 wk ODM和2 wk TDM。实施3周的ODM可使牛奶产量平均降低27.5％，恢复TDM后，奶牛平均损失了57％的牛奶。TDM控制期和3周ODM期间的遗传力估计分别为：牛奶产量分别为0.41和0.35，牛奶脂肪含量为0.66和0.61，牛奶蛋白质含量为0.60和0.80，牛奶乳糖含量为0.66和0.36、0.20牛奶的体细胞分数含量为0.15。3周ODM和TDM期间的产奶量和组成在遗传上接近（实验期之间的性状内遗传相关性均超过0.80），但在相同挤奶频率内在遗传上更接近。在将奶牛改为ODM时观察到的产奶率遗传力中等（产奶率分别为kg / d和％的产奶率分别为0.39和0.34），中等，与产奶率相似。恢复TDM后的产奶量恢复（kg / d）是高遗传力（0.63）的一个特征。由于它们易于测量，因此对ODM第一天的TDM产奶量和组成以及产奶量响应进行了研究，以此作为对3-wk ODM产奶量响应的预测指标，从而轻松检测出非常适合ODM的动物。每天两次挤奶的牛奶产量和组成被发现与牛奶产量响应在遗传上部分相关，但对于实际应用而言还不够紧密。遗传相关系数为0.98和0.96与3周ODM的牛奶产量损失（分别以kg / d和％表示），事实证明，ODM第一天的牛奶产量损失比长期ODM的预测牛奶产量响应更准确TDM牛奶产量。在ODM的第一天，研究了TDM的产奶量和组成以及产奶量响应，作为对3-wk ODM产奶量响应的预测指标，以轻松检测出非常适合ODM的动物。每天两次挤奶的牛奶产量和组成被发现与牛奶产量响应在遗传上部分相关，但对于实际应用而言还不够紧密。遗传相关系数为0.98和0.96与3周ODM的牛奶产量损失（分别以kg / d和％表示），事实证明，ODM第一天的牛奶产量损失比长期ODM的预测牛奶产量响应更准确TDM牛奶产量。在ODM的第一天，研究了TDM的产奶量和组成以及产奶量响应，作为对3-wk ODM产奶量响应的预测指标，以轻松检测出非常适合ODM的动物。每天两次挤奶的牛奶产量和组成被发现与牛奶产量响应在遗传上部分相关，但对于实际应用而言还不够紧密。遗传相关系数为0.98和0.96与3周ODM的牛奶产量损失（分别以kg / d和％表示），事实证明，ODM第一天的牛奶产量损失比长期ODM的预测牛奶产量响应更准确TDM牛奶产量。每天两次挤奶的牛奶产量和组成被发现与牛奶产量响应在遗传上部分相关，但对于实际应用而言还不够紧密。遗传相关系数为0.98和0.96与3周ODM的牛奶产量损失（分别以kg / d和％表示），事实证明，ODM第一天的牛奶产量损失比长期ODM的预测牛奶产量响应更准确TDM牛奶产量。每天两次挤奶的牛奶产量和组成被发现与牛奶产量响应在遗传上部分相关，但对于实际应用而言还不够紧密。遗传相关系数为0.98和0.96与3周ODM的牛奶产量损失（分别以kg / d和％表示），事实证明，ODM第一天的牛奶产量损失比长期ODM的预测牛奶产量响应更准确TDM牛奶产量。