Milk progesterone profiles and their relationship with fertility, production and disease in dairy cows in Northern Ireland

A detailed investigation was conducted to identify the main factors influencing the current poor reproductive performance in dairy herds in Northern Ireland. Nineteen herds were selected and a comprehensive database was established, comprising detailed information collected over a 2-year period. Milk progesterone monitoring (no.=1423 cows), based on twice weekly sampling, was included in this on-farm investigation. The mean interval from calving to commencement of luteal activity was 30.1 days and 13.4% (184/1378) of these cows had not commenced luteal activity by day 50 post partum. In addition, there was a high incidence of abnormal progesterone profiles: delayed ovulation type I; 15.6% (242/1388), delayed ovulation type II; 11.7% (125/965), persistent corpus luteum type I; 19.4% (212/1121) and persistent corpus luteum type II; 11.9% (70/619). Delayed commencement of luteal activity and abnormal profiles were associated with reduced fertility performance manifested as increased interval to first AI service and ultimately prolonged calving interval. Delayed commencement of luteal activity and abnormal progesterone profiles, with the exception of 'delayed ovulation type II' profiles, were not associated with lower conception rates. Assistance at calving was associated with delayed commencement of luteal activity. Delayed commencement of luteal activity and delayed ovulation types I and II profiles were associated with indicators of nutritional stress and poorer production performance in early lactation. Retained foetal membranes were strongly associated with prolonged luteal phases (persistent corpus luteum types I and II profiles). While hormonal therapy may prove useful in treating cows with abnormal milk progesterone profiles, the prevention and treatment of associated diseases and the implementation of good management practices are likely to be more rewarding.