Effect of PRID administered 5-11 days after insemination on the probability of pregnancy in lactating dairy cows
This thesis is an evaluation of the efficacy of a Progesterone Releasing Intravaginal Device (PRID, 1.55g Progesterone) administered after insemination to combat progesterone insufficiency which is believed to decrease the risk of pregnancy in lactating dairy cows. A field trial was conducted in which 991 lactating Holstein cows were enrolled 5 to 11 days post-insemination and randomly assigned to receive a PRID or PID (placebo intravaginal device) for 7 days. Serum progesterone concentrations were measured at insertion (5-11 days post-insemination) and removal (12-18 days post-insemination) of devices. The risk of pregnancy in cows 30-60 days after-insemination was not different between cows that received PRID or PID. Serum progesterone levels were elevated at the time of device removal in PRID treated cows compared to PID cows. Progesterone concentrations from 5-11 and 12-18 days post-insemination were positively associated with the risk of pregnancy.