Factors affecting reproductive performance of dairy cows in a pasture-based, automatic milking system research farm: a retrospective, single-cohort study

12 April 2016

A retrospective single cohort study was conducted to identify production and health factors associated with reproductive performance in a pasture-based automatic milking system research farm. The calving system of this herd shifted from split calving to year round calving gradually during the study period. Data from 365 cows with 798 lactations were analysed in the study. Reproductive outcome variables of interest were intervals from calving to first oestrus, to first insemination, and to conception as well as number of inseminations per conception, probability of submission for insemination by 80 days in milk, probability of conception by 100 days in milk and probability of conception at first insemination. Production factors (milk yield and its composition; milking frequency), record of periparturient disease, parity and season of calving were considered as predictor variables. The associations between predictor and outcome variables were assessed by multivariable linear regression, logistic regression and survival analyses for quantitative, binary and time-to-event outcomes, respectively. Average milk yield and milking frequency during 100 days in milk were not significantly associated with any of the reproductive measures. The likelihood of conception by 100 days in milk decreased gradually with year of automatic milking systems commissioning. Cows calved in autumn were 43% (hazard ratio: 1.43, P < 0.05) more likely to conceive compared to cows that calved in summer. Multiparous cows were more likely (P < 0.05) to be recorded for oestrus compared to primiparous cows. Twinning was negatively associated with the reproductive outcomes measured in the automatic milking systems research herd. Milk yield and milking frequency during 100 days in milk had no effect on reproductive measures in the pasture-based automatic milking system research herd. Key words: Reproduction, Automatic Milking System, Pasture-Based System