Strategies for reversing the trend towards subfertility in dairy cattle

The calving rate of the modern dairy cow is declining at approximately 1% p er 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 her e 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 sub fertility; firstly, they allow the identification of specific reproductive abnormalities which can be treated pharmacologically. Secondly, they show t hat at least one endocrinopathy is heritable, thereby providing the basis f or a selective breeding strategy. Thirdly, they provide a means for monitor ing ovarian (and indirectly uterine and conceptus) function during early pr egnancy, which are central to the successful establishment of pregnancy, an d are amenable to dietary modification. These approaches to reversing the f alling fertility of dairy cows are characterized by different timescales. ( C) 2000 Harcourt Publishers Ltd.