Genetic Parameters for Milk Yield, Milk Electrical Conductivity and Milk Flow Rate in First-Lactation Jersey Cows in Sri Lanka

Milk electrical conductivity is an indicator trait for mastitis, and for maintaining udder health, moderate milking speed is important. The heritabilities of sum of daily milk yields, mean milk electrical conductivity and mean milk flow rate for each 30-day period along the lactation trajectory in Jersey cows milking in their first lactation in Sri Lanka were estimated. The data included 248,854 daily records and 362,754 morning and evening records from 991 cows that calved from 2015 to 2018. Variance components and variance ratios were estimated from posterior means obtained from a Gibbs sampler. The heritability as estimated by univariate analyses for milk yield, milk electrical conductivity and milk flow rate ranged from 0.04 ± 0.01 to 0.13 ± 0.03, from 0.06 ± 0.02 to 0.09 ± 0.02, and from 0.06 ± 0.02 to 0.18 ± 0.05, respectively. Additive genetic correlations between milk yield and milk electrical conductivity or milk flow rate along the lactation ranged from -0.31 ± 0.49 to 0.77 ± 0.19 and from 0.46 ± 0.29 to 0.89 ± 0.12, respectively. Present heritability estimates were sufficiently high for milk electrical conductivity and flow rate to be used in a selection index. However, these estimates should be confirmed with more data.