Gonadotropin Induced Multiple Births in Beef Cows Following Estrus Synchronization

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Abstract
Sixty-five lactating multiparous beef cows were utilized to compare the effectiveness in inducing multiple births of a sequence of two PMSG injections timed from either a naturally occurring or a progestogen synchronized estrus. Estrus was synchronized by individually feeding CAP. All cows received subcutaneous injections of PMSG, 1,080 IU on day-5 and 1,440 IU on day-17 of the cycle, with an intravenous injection of 2,500 IU HCG given at time of mating or insemination. Four treatments were imposed: treatment I — not estrus synchronized, breeding by natural service; treatment II — estrus synchronized, breeding by natural service; treatment III — estrus synchronized, breeding by artificial insemination at post-PMSG estrus; treatment IV — estrus synchronized, all cows bred by artificial insemination on days-3 and 4 post-PMSG. Conception rate at first post-PMSG estrus was higher in treatment I than in treatment II (P<.05) or treatments III or IV (P<.01). The conception rate for the total 60 to 90 day breeding season was also lower in all estrus synchronized groups. Copyright © 1975. American Society of Animal Science . Copyright 1975 by American Society of Animal Science