Extended voluntary waiting period before first insemination in primiparous dairy cows : effects on milk production, fertility, and health

Sammanfattning: Extension of the voluntary waiting period (VWP) before first insemination after calving, could decrease the frequency of demanding transition periods both at cow and herd level. In the initial study of this thesis, the cows were randomized to an extended (155-205 d) or conventional (35-85 d) VWP and assessed during their first and second lactation. In a later study on customized extended VWP, cows expected to be suited for extended VWP were selected based on high genomic persistency index, calving difficulties or disease in early lactation, and high early lactation yield, and then randomly allocated to extended (≥185) or conventional (≤90) VWP.For cows with randomized extended compared with conventional VWP, milk yield per day in the calving interval was maintained during the first lactation and higher during the second lactation, milk yield before dry-off was lower and reproductive performance was improved. Cows with customized extended VWP showed similar improvements compared with cows expected to be suited for an extended but receiving conventional VWP, but in contrast to the randomized study, the dry period was not longer for cows randomized to customized extended VWP. Extending the VWP had no effect on disease incidence and culling rate. Extended VWP for primiparous cows in high-yielding herds can thus make use of modern dairy cows’ great potential for milk production and fertility, thereby potentially increasing flexibility and resilience in dairy herds.