Summary. Milk

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A progesterone-releasing intravaginal device (PRID) was inserted for 14 days into 10 lactating dairy cows at least 50 days after calving. Synchronization of oestrus was good and 5 of the cows conceived to a double insemination 48 and 72 h after PRID removal. In 9 cows vaginal infection was present when the PRID was removed but resolved spontaneously. The level of progesterone in the milk and the milk yield were similar to those in the 10 control animals. PRID treatment of 9 cows whose ovaries had remained inactive for at least 50 days after calving was followed by ovulation, as judged by the milk progesterone profile, in 8 animals after removal of the device.

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.