Influence of early post partum ovulation on the re-establishment of pregnancy in multiparous and primiparous dairy cattle.

To investigate the influence of early ovulation after calving on subsequent fertility, milk progesterone concentrations were monitored twice weekly in multiparous (n = 87) and primiparous (n = 60) Holstein/Friesian dairy cattle. Luteal activity before 21 days post partum was defined as 'early'. In multiparous cows, calving-to-conception interval (CCI) was longer, services per cow were more numerous and conception rate to all inseminations was lower with early luteal activity (n = 41, 16.8 +/- 0.39 days post partum) than with later luteal activity (n = 46, 37.8 +/- 2.09 days post partum); multiparous cows with early luteal activity required more exogenous fertility treatments and were more likely to fail to conceive by 100 days post partum. In contrast, in primiparous cows, no significant relationships were detected between early (n = 32) or later (n = 28) luteal activity and the CCI, number of services per cow or conception rates to all inseminations. However, primiparous cows that ovulated before 21 days post partum had fewer normal progesterone profiles. Early ovulation after calving was associated with reduced pregnancy rates and prolonged CCIs in multiparous but not in primiparous dairy cows.