The high-producing dairy cow and its reproductive performance.

There is evidence that the reproductive performance of dairy cows has declined as milk yields have increased over the last 40 years. Identifying the precise cause(s) of this problem may provide focused solutions. Intensive genetic selection for very high yields has reduced fertility, due mainly to an increase in postpartum clinical problems, poor expression of oestrus, defective oocytes/embryos and uterine infections. It is a challenge to solve the problem by getting enough food into these cows to meet the high demands of peak milk yields in early lactation, as well as providing the considerable veterinary attention required in the early period after calving. Both these aspects also pose welfare issues. A better solution would be to make genetic and management changes to increase the persistency of lactations to reduce the number and intensity of clinical risk periods throughout a cow's life without compromising milk output.