Evaluation of a contract breeding management program in selected Ohio dairy herds with event-time analysis

All frailty terms were highly significant, regardless of whether it was an individual frailty at the lactation level or a shared frailty at the cow or herd level, suggesting that there was considerable heterogeneity within these levels. Inclusion of a frailty term at the herd level changed the estimate for the contract breeding program considerably, while a frailty term on other levels did not, indicating that herd characteristics (e.g., overall management) have a substantial impact on reproductive performance and should be accounted for in the analysis. Interpretation using time ratios with or without a shared herd frailty found that the contract breeding program was associated with a reduction of 6.5% and 14.1% in mean time to pregnancy, respectively.