Strategies for reversing the trend towards subfertility in dairy cattle

The calving rate of the modern dairy cow is declining at approximately 1% per annum. First service conception rates are now below 40%, and the average cow requires more than two inseminations to get her in calf. We review here genetic, endocrine and nutritional strategies for reducing subfertility, and we emphasize the role of milk progesterone data in the analysis of the condition. Milk progesterone data underpin three approaches to treating subfertility; firstly, they allow the identification of specific reproductive abnormalities which can be treated pharmacologically. Secondly, they show that at least one endocrinopathy is heritable, thereby providing the basis for a selective breeding strategy. Thirdly, they provide a means for monitoring ovarian (and indirectly uterine and conceptus) function during early pregnancy, which are central to the successful establishment of pregnancy, and are amenable to dietary modification. These approaches to reversing the falling fertility of dairy cows are characterized by different timescales.