Cases of prolonged luteal activity in the non-pregnant dairy cow

Regular measurements of progesterone in milk were made to monitor ovarian activity in over 300 commercial dairy cows from partiurition until pregnancy established. Six animals (approximately 1-5 per cent) which had not previously been inseminated showed prolonged luteal activity lasting for over 30 days. No apparent uterine abnormalities or infections were found in these cases. Prostaglandin analogue cloprostenol (Estrumate ICI) given intramuscularly induced complete luteolysis in treated animals. The subsequent fertility varied, but at least three of the six cows conceived again.