Milkability is an important functional trait, which is directly related to milking costs and udder health. There are no milkability traits incorporated in the South African dairy cattle breeding objectives and genetic parameter estimates for these traits are not available in this population. The main objective of the study was, therefore, to estimate the genetic parameters for milkability traits and its correlation with somatic cell scores in South African Holstein cattle. Data consisted of production and milkability records of 2719 Holstein cows, from ten herds, collected from 2016 to 2018. Genetic parameters were estimated by a multi-trait animal model using the restricted maximum likelihood (REML) procedure. Means for milking time (MT), average milk flow (AMF), maximum milk flow (MMF), and somatic cell score (SCS) were 5.20 min, 1.91 kg/min, 2.99 kg/min, and 2.06, respectively. The heritability estimates were low to moderate from 0.19 ± 0.07, 0.24 ± 0.06, 0.36 ± 0.11, and 0.41 ± 0.12, respectively, for SCS, AMF, MT, and MMF. The genetic correlations were significant (P < 0.05) among the three milkability traits ranged from − 0.31 ± 0.05 between AMF and MT to 0.85 ± 0.02 between AMF and MMF. Positive genetic correlations were observed between AMF and MMF, while the correlations for MT with the remaining milkability traits were negative. Genetic correlations of SCS with AMF, MMF, and MT were − 0.13 ± 0.04, 0.13 ± 0.04, and − 0.25 ± 0.12, respectively. The mean estimated breeding value (EBV) was estimated using cattle birth dates, and there was an increase in AMF of 0.0001 kg/min EBV per year on cattle born during the period 2002 to 2014. Maximum milk flow also showed an increasing genetic trend of 0.0003 kg/min per year over the same period. On the other hand, the genetic trend for MT was undesirable, as it increased by 0.0003 kg/min per year. The moderate to high heritability estimates for milkability traits showed that selection for improvement was possible in South African Holstein cattle. High genetic correlation between AMF and MMF implied that these two may be regarded as the same trait. Milking time can contribute towards improving the accuracy of estimating EBVs for SCS in a multi-trait analysis, and vice versa, due to the moderate correlation between the two traits. The marginal genetic trend in milkability traits may be an interrelated response to selection of other traits already under selection in the population such as SCS. Results of the current study provided a basis for including milkability traits of South African Holstein cattle in the breeding objectives.

挤奶能力是一项重要的功能性状，与挤奶成本和乳房健康直接相关。南非奶牛育种目标中未包含可挤奶性状，并且这些性状的遗传参数估计不可用。因此，这项研究的主要目的是估计南非荷斯坦牛的可乳性特征的遗传参数及其与体细胞评分的相关性。数据包括2016年至2018年收集的来自十个牛群的2719头荷斯坦奶牛的生产和挤奶记录。遗传基因参数使用限制最大似然（REML）方法通过多性状动物模型进行估算。挤奶时间（MT），平均牛奶流量（AMF），最大牛奶流量（MMF）和体细胞评分（SCS）的平均值为5.20分钟，1.91千克/分钟，2。分别为99 kg / min和2.06。对于SCS，AMF，MT和MMF，遗传力估计值分别从0.19±0.07、0.24±0.06、0.36±0.11和0.41±0.12低至中等。遗传相关性显着（P <0.05）的三个乳化性状介于AMF和MT之间的-0.31±0.05至AMF和MMF之间的0.85±0.02。在AMF和MMF之间观察到正的遗传相关性，而MT与剩余的可挤奶性状的相关性为负。SCS与AMF，MMF和MT的遗传相关性分别为-0.13±0.04、0.13±0.04和-0.25±0.12。平均估计育种价值（EBV）是根据牛的出生日期估算的，并且2002年至2014年期间出生的牛的AMF每年增加0.0001 kg / min EBV。同期为每年0.0003千克/分钟。另一方面，MT的遗传趋势是不希望的，因为它以每年0.0003kg / min的速度增加。从中到高的遗传力估计，可测出牛奶性状表明，南非荷斯坦奶牛的改良选择是可能的。AMF和MMF之间的高度遗传相关性暗示这两个可被视为同一性状。由于两个特征之间的适度相关性，挤奶时间可以有助于提高在多特征分析中估算用于SCS的EBV的准确性，反之亦然。乳汁性状的边际遗传趋势可能是对人口中已经在选择中的其他性状（如南南合作）的相互反应。目前的研究结果为将南非荷斯坦牛的乳性特征纳入育种目标提供了基础。AMF和MMF之间的高度遗传相关性暗示这两个可被视为同一性状。由于两个特征之间的适度相关性，挤奶时间可以有助于提高在多特征分析中估算用于SCS的EBV的准确性，反之亦然。乳汁性状的边缘遗传趋势可能是对人口中已经在选择中的其他性状（如南南合作）的相互反应。目前的研究结果为将南非荷斯坦牛的乳性特征纳入育种目标提供了基础。AMF和MMF之间的高度遗传相关性意味着这两个特征可以被视为同一性状。由于两个特征之间的适度相关性，挤奶时间可有助于提高在多特征分析中估算用于SCS的EBV的准确性，反之亦然。乳汁性状的边际遗传趋势可能是对人口中已经在选择中的其他性状（如南南合作）的相互反应。目前的研究结果为将南非荷斯坦牛的乳性特征纳入育种目标提供了基础。乳汁性状的边际遗传趋势可能是对人口中已经在选择中的其他性状（如南南合作）的相互反应。目前的研究结果为将南非荷斯坦牛的乳性特征纳入育种目标提供了基础。乳汁性状的边缘遗传趋势可能是对人口中已经在选择中的其他性状（如南南合作）的相互反应。目前的研究结果为将南非荷斯坦牛的乳性特征纳入育种目标提供了基础。