The effect of estrus synchronization and post-partum interval on fertility in beef cattle

22and Dhindsa et al .(1967) reported conception rates similar to controls following treatment with MAP.However, Hansel et al .(1961) reported lowered fertility after MAP.Zimbelman (I963) determined that 135 mg daily was the minimum dose for synchronization of estrus in heifers with MAP.Dhindsia et al. (1967) reported the number of times per day that MAP was fed was insignificant, and a higher percentage of heifers than cows showed heat after MAP treatment.MAP fed at 2^-0 mg per day for 18 days resulted in a significantly higher conception rate than CAP fed at 10 mg per day for 18 days (Hansel et al. 1966).Van Blake et al .(1963) reported synchronized estrus occurred 6 to 9 days after hormone withdrawal when heifers were fed 12 mg of CAP per day for 18 days, and conception rate equaled that of untreated controls.Grunert (1975) fed 10 mg of CAP per day for 18 days and administered 5 mg EB (estradiol benzoate) two days after CAP withdrawal.He reported an increase in estrus intensity, but no change in conception rate with EB j however, when he injected 1.5 mg of GnRH (gonadotropin releasing hormone) 5 hr before insemination, conception rate improved.HCG (human chorionic gonadotropin) administered after an 18 day CAP treatment reduced the percentage in estrus but increased conception rate (Baker and Coggins , 1968) Feeding of MGA increases growth and improves feed effi- ciency in feedlot heifers (Bloss et al ., 1966; O'Brien et al .1968).MGA.feeding also synchronizes estrus by suppressing heat in both heifers and cows, but like other progestogens,