Haile-Mariam M, Pryce J E
Biosciences Research Division, Department of Economic Development, Jobs, Transport and Resources, Agribio, 5 Ring Road, La Trobe University, Bundoora, VIC 3083, Australia.
Biosciences Research Division, Department of Economic Development, Jobs, Transport and Resources, Agribio, 5 Ring Road, La Trobe University, Bundoora, VIC 3083, Australia; School of Applied Systems Biology, La Trobe University, Bundoora, VIC 3083, Australia.
J Dairy Sci. 2017 May;100(5):3754-3766. doi: 10.3168/jds.2016-11952. Epub 2017 Mar 9.
Lactose is a major component of milk (typically around 5% of composition) that is not usually directly considered in national genetic improvement programs of dairy cattle. Daily test-day lactose yields and percentage data from pasture-based seasonal calving herds in Australia were analyzed to assess if lactose content can be used for predicting fitness traits and if an additional benefit is achieved by including lactose yield in selecting for milk yield traits. Data on lactose percentage collected from 2007 to 2014, from about 600 herds, were used to estimated genetic parameters for lactose percentage and lactose yield and correlations with other milk yield traits, somatic cell count (SCC), calving interval (CIV), and survival. Daily test-day data were analyzed using bivariate random regression models. In addition, multi-trait models were also performed mainly to assess the value of lactose to predict fitness traits. The heritability of lactose percentage (0.25 to 0.37) was higher than lactose yield (0.11 to 0.20) in the first parity. Genetically, the correlation of lactose percentage with protein percentage varied from 0.3 at the beginning of lactation to -0.24 at the end of the lactation in the first parity. Similar patterns in genetic correlations were also observed in the second and third parity. At all levels (i.e., genetic, permanent environmental, and residual), the correlation between milk yield and lactose yield was close to 1. The genetic and permanent environmental correlations between lactose percentage and SCC were stronger in the second and third parity and toward the end of the lactation (-0.35 to -0.50) when SCC levels are at their maximum. The genetic correlation between lactose percentage in the first 120 d and CIV (-0.23) was similar to correlation of CIV with protein percentage (-0.28), another component trait with the potential to predict fertility. Furthermore, the correlations of estimated breeding values of lactose percentage and estimated breeding values of traits such as survival, fertility, SCC, and angularity suggest that the value of lactose percentage as a predictor of fitness traits is weak. The results also suggest that including lactose yield as a trait into the breeding objective is of limited value due to the high positive genetic correlation between lactose yield and protein yield, the trait highly emphasized in Australia. However, recording lactose percentage as part of the routine milk recording system will enable the Australian dairy industry to respond quickly to any future changes and market signals.
乳糖是牛奶的主要成分（通常约占成分的5%），在奶牛的国家遗传改良计划中通常不被直接考虑。对澳大利亚以牧场为基础的季节性产犊牛群的每日测定日乳糖产量和百分比数据进行了分析，以评估乳糖含量是否可用于预测健康性状，以及在选择产奶性状时纳入乳糖产量是否能带来额外益处。利用2007年至2014年从约600个牛群收集的乳糖百分比数据，估计乳糖百分比和乳糖产量的遗传参数以及与其他产奶性状、体细胞计数（SCC）、产犊间隔（CIV）和存活率的相关性。使用双变量随机回归模型分析每日测定日数据。此外，还进行了多性状模型分析，主要是为了评估乳糖对预测健康性状的价值。头胎中乳糖百分比的遗传力（0.25至0.37）高于乳糖产量的遗传力（0.11至0.20）。从遗传角度来看，头胎中乳糖百分比与蛋白质百分比的相关性在泌乳初期为0.3，在泌乳末期为-0.24。在二胎和三胎中也观察到了类似的遗传相关性模式。在所有水平（即遗传、永久环境和残差）上，产奶量与乳糖产量之间的相关性接近1。在二胎和三胎以及泌乳末期（此时SCC水平最高），乳糖百分比与SCC之间的遗传和永久环境相关性更强（-0.35至-0.50）。前120天的乳糖百分比与CIV之间的遗传相关性（-0.23）与CIV与蛋白质百分比之间的相关性（-0.
