Effect of a progesterone-releasing intravaginal device on the milk progesterone levels, vaginal flora, milk yield and fertility of cyclic and non-cyclic dairy cows.

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.