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Milk yield is the primary trait of importance in a dairy cattle breeding objective. In terms of the milk parlor efficiency, selection for more uniform and intermediate optimum milking duration is important. Therefore, genetic parameters for milking duration under an intensive management system of first lactation Jersey cows in Sri Lanka were estimated. Morning and evening milk production records from 260 to 305 days in milk (595 cows, at least 30 records per cow) were used to estimate session mean milking duration (MD). Outliers that differed by more than four standard deviations from the mean were excluded. The minimum size of the contemporary group was ten. Variance components were estimated following Bayesian approach using a blocked Gibbs sampler and taking the means of conditional posterior distributions, by fitting animal and sire models with month and milk yield as the fixed effect and covariate. The total number of animals in the pedigree was 1015. Descriptive statistics indicated a mean MD of 277.9±33.94 seconds for 5.45±1.38 liters of milk (51.0 seconds for milking a liter of milk). Heritability estimates obtained using an animal model were 0.17±0.05 and using a sire model 0.15±0.03 for MD. Mixed models in R software produced a heritability estimate of 0.12 using a sire model that ignored pedigree. Phenotype variances obtained from Gibbs sampler and R were 782.1 and 841.5, respectively. Heritability estimates indicate that MD can be effectively included in the dairy breeding objective of Sri Lanka to breed cows with optimal milking duration. |
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