Puberty in Beef Heifers. III. Induction of Fertile Estrus

Abstract

By utilizing estrogen and progesterone, it appeared possible to mimic the changes occurring in blood hormone levels near puberty. This suggested the possibility of induction of puberty in beef heifers. Four trials were conducted to test this hypothesis and a fifth to explore the effect of treatment with steroids in induction of estrus in suckling anestrous cows. Trial 1. At the Eastern Colorado Range Station, 45 Hereford, Angus-Hereford and Charolais-Hereford heifers were divided within breed into a control group (C), Group I which received on day 1 a single IM injection of 5 mg of estradiol valerate (EV) plus 3 mg of 17α-acetoxy 11 beta-methyl 19 nor-preg-4ene 3, 20 dione (norgestomet), and a 6 mg ear implant of norgestomet which was removed 9 days later, and group P which received 5 mg of estradiol valerate, IM on day 6, daily IM injections of 20 mg of progesterone from day 6 to day 10 and 2 mg of estradiol-17ß on day 12. By 4 days after implant removal, estrus was detected in 0,94 and 93% for groups C, I and P, respectively.