The Hormonal Control of Estrus and Ovulation in the Beef Heifer

Abstract

Studies involving 179 beef heifers were conducted to determine if estrus and ovulation could be controlled by limited hormonal treatment. A single injection of from 540–1120 mg. of crystalline progesterone in starch emulsion was capable of preventing estrus and ovulation in all of the treated heifers, regardless of the stage of the estrous cycle when treatment was given. Estrus occurred 15–19 days after the progesterone injection in 89% of the heifers receiving 540–560 mg. of progesterone, and 15–23 days after the progesterone injection in heifers receiving 700–1120 mg. of progesterone; ovulation occurred in 95% of the heifers examined following this controlled estrus. Normal pregnancy resulted in the two heifers inseminated at the controlled estrus. When the initial injection of 560 mg. of progesterone was followed 15 days later by a single injection of equine gonadotrophin in normally cycling heifers,90% came in heat 16–19 days after the progesterone injection or 1–4 days following the gonadotrophin injection. A single ovulation or multiple ovulations were demonstrated to have occurred in all heifers examined at the post-injection estrus. The conception rate (17%) was very low with this method of treatment. Copyright © . .