Pregnancy rates in cows and heifers inseminated at predetermined times using progesterone-releasing intravaginal devices

The time of estrus and ovulation were controlled using a proges-terone-releasing intravaginal device constructed from silicone rubber. Pregnancy rates were determined in beef cows and heifers inseminated with frozen semen at predetermined times after removal of the device. Two experiments were conducted using two types of devices. In experiment I, a sleeve-covered device was inserted into the vagina and left for 21 days. Thirty-six hours after the devices were removed each animal received 100 μg of synthetic GnRH intramuscularly and was inseminatec 48 hours after coil removal. Five percent of the heifers lost coils during the 21-day treatment period compared to 25% of mature cows. First service pregnancy rate was 26%. In experiment II, a PRID^® was used for a 14-day treatment period. Animals were not treated with GnRH as in experiment I and were inseminated from 56 to 68 hours after PRID removal. Only 3.5% of the coils were lost during the 14 days. Pregnancy rates ranged from 13 to 60%.