Some Effects of Sole Pasture Diets on Reproductive Performance of Lactating Cows in Seasonal Dairy Herds

The reproductive performance of 631 dairy cows in 5 herds which had a single concentrated calving programme in late winter was monitored through the post-partum period and the breeding programme. The cows in ench herd were of high genetic merit and received a sole ration of pasture grazed in situ. Anoestrous animals which had failed to ovulate since calving were identified before the start of the breeding programme. The average post-partum interval to first oestrus was 48.5 days, but ranged from 35.7 to 58,5 days in individual herds. It was 86.6 days in the anoestrous cows which represented 18.7% of the total numbers. The pasture feeding system prolonged the interval to conception when it contributed to the incidence of anoestrum. Oestrous detection rates and pregnancy rates were comparatively high once cows had started cycling.