Poor reproductive performance of dairy herds is seldom attributable to a high incidence of embryonic loss or to long periods of anoestrus, but is generally due to the failure to inseminate cows that are cycling normally.

Even in the best managed herds, oestrus detection rates rarely exceed 70-80%, and often 10-20% of non-oestrous animals may be recorded as being on heat. These shortcomings in oestrus detection can be overcome by monitoring oestrous cycles in Individual animals, thus enabling the time of ovulation to be predicted. For example, when cows that failed to show oestrus, were inseminated on the basis of milk progesterone profiles, the conception rates achieved were similar to those in cows inseminated at observed oestrus (Ball and Jackson, 1979). In addition, in groups of animals inseminated at progesterone-timed rather than at observed oestrus, the number of cows served over a one-cycle period increased dramatically (98 v 71%), and days from calving to first service decreased (78 v 92 days), (Foulkes, Cookson and Sauer, 1982). In this study, the feasibility of using on-farm milk progesterone kits as a practical method of predicting ovulation, and its effects on herd reproductive performance were assessed.