Jayawardana J M D R, Lopez-Villalobos N, McNaughton L R, Hickson R E
School of Agriculture and Environment, Massey University, Palmerston North 4410, New Zealand; Department of Animal Science, Faculty of Animal Science and Export Agriculture, Uva Wellassa University, Badulla 90000, Sri Lanka.
School of Agriculture and Environment, Massey University, Palmerston North 4410, New Zealand.
J Dairy Sci. 2023 Mar;106(3):1910-1924. doi: 10.3168/jds.2022-22431. Epub 2023 Jan 27.
The objectives of this study were to estimate the genetic and phenotypic correlations and heritabilities for milk production and fertility traits in spring-calved once-daily (OAD) milking cows for the whole season in New Zealand and compare those estimates with twice-daily (TAD) milking cows. Data used in the study consisted of 69,252 first parity cows from the calving seasons 2015-2016 to 2017-2018 in 113 OAD and 531 TAD milking herds. Heritability estimates for production and fertility traits were obtained through single-trait animal models, and estimates of genetic and phenotypic correlations were obtained through bivariate animal models. Heritability estimates of production traits varied from 0.26 to 0.61 in OAD and from 0.13 to 0.63 in TAD. Heritability estimates for fertility traits were low in both OAD and TAD milking cow populations, and estimates were consistent (OAD: 0.01 to 0.10 and TAD: 0.01 to 0.08) across milking regimens. Estimates of phenotypic and genetic correlations among production traits were consistent across populations. In both populations, phenotypic correlations between milk production and fertility traits were close to zero, and most of the genetic correlations were antagonistic. In OAD milking cows, genetic correlations of milk and lactose yields with the start of mating to conception, 6-wk in-calf, not-in-calf, and 6-wk calving rate were close to zero. Interval from first service to conception was negatively genetically correlated with milk and lactose yields in OAD milking cows. Protein percentage was positively genetically correlated with 3-wk and 6-wk submission, 3-wk in-calf, 6-wk in-calf, first service to conception, 3-wk calving, and 6-wk calving rate in the TAD milking cow population, but these correlations were low in the OAD milking cow population. Further studies are needed to understand the relationship of protein percentage and fertility traits in the OAD milking system. The phenotypic correlations between fertility traits were similar in OAD and TAD milking populations. Genetic correlations between fertility traits were strong (≥0.70) in cows milked TAD, but genetic correlations varied from weak to strong in cows milked OAD. Further research is required to evaluate the interaction between genotype by milking regimen for fertility traits in terms of sire selection in the OAD milking cow population.
本研究的目的是估计新西兰春季产犊且每日挤奶一次（OAD）的奶牛整个产季产奶量和繁殖性状的遗传及表型相关性与遗传力，并将这些估计值与每日挤奶两次（TAD）的奶牛进行比较。本研究使用的数据包括来自113个OAD和531个TAD挤奶牛群的2015 - 2016年至2017 - 2018年产犊季的69252头头胎奶牛。通过单性状动物模型获得生产和繁殖性状的遗传力估计值，通过双变量动物模型获得遗传和表型相关性估计值。OAD产奶性状的遗传力估计值在0.26至0.61之间，TAD在0.13至0.63之间。OAD和TAD挤奶牛群中繁殖性状的遗传力估计值都较低，且在不同挤奶方式下估计值一致（OAD：0.01至0.10，TAD：0.01至0.08）。不同群体间生产性状的表型和遗传相关性估计值一致。在两个群体中，产奶量与繁殖性状之间的表型相关性接近零，且大多数遗传相关性呈拮抗关系。在OAD挤奶牛中，牛奶和乳糖产量与配种开始至受孕、怀孕6周、未怀孕以及怀孕6周产犊率的遗传相关性接近零。在OAD挤奶牛中，首次输精至受孕间隔与牛奶和乳糖产量呈负遗传相关。在TAD挤奶牛群体中，蛋白质百分比与3周和6周输精、怀孕3周、怀孕6周、首次输精至受孕、怀孕3周产犊以及怀孕6周产犊率呈正遗传相关，但在OAD挤奶牛群体中这些相关性较低。需要进一步研究以了解OAD挤奶系统中蛋白质百分比与繁殖性状之间的关系。OAD和TAD挤奶群体中繁殖性状之间的表型相关性相似。TAD挤奶的奶牛繁殖性状之间的遗传相关性很强（≥0.70），但OAD挤奶的奶牛遗传相关性从弱到强不等。需要进一步研究以评估在OAD挤奶牛群体中就种公牛选择而言，挤奶方式与基因型之间对繁殖性状的相互作用。
