Reproduction management in dairy cattle: a prospective study using progesterone and oestrone sulphate for monitoring pregnancy

In a prospective 2-year study, milk progesterone and oestrone sulphate determinations were used to monitor and assess pregnancy in lactating cows. The testing was done centrally at a government regional veterinary establishment which was responsible for providing semen to the farms of the area and also had available specialist expertise in animal reproduction. Sample collection and dissemination of test results were achieved through the network of the artificial insemination service. This approach was preferred because it was considered ergonomic, cost-effective and reliable. Comparison of oestrus behavioural signs and progesterone on the day of insemination revealed that 7·8% (89/1133) of the animals tested had high progesterone levels. Single progesterone testing on day 21 post insemination was not satisfactory for pregnancy diagnosis as the positive predictive value was 83·0% (147/177). The combination of low progesterone on day 0 and high progesterone on day 21 improved the positive predictive value to 87·4% (235/269). Results from 400 samples taken 110 to 130 days post insemination from 53 animals revealed that cows with oestrone sulphate concentrations greater than 0·1 μg/l actually calved. This assay appears to be particularly suitable as a pregnancy confirmation test. A pilot field study implementing a programme of testing on days 0, 21 and 42 for progesterone and between days 110 to 130 for oestrone sulphate not only achieved almost absolute pregnancy predictive values but careful result analysis strongly indicated that the approach of systematic testing can also reveal the fertility profile of a given herd and help to identify potential causes of pregnancy failure from the period of the reproduction cycle in which they occur.