Synchronization of follicular wave emergence, luteal regression, and ovulation for fixed-time artificial insemination in beef cows and heifers

摘要

Two experiments tested the efficacy of gonadotropin-releasing hormone(GnRH) or estradiol cypionate (ECP) administration in combination withcontrolled internal drug release (CIDR) inserts on pregnancy rate to fixed-timeartificial insemination (FTAI) in beef heifers. In the first experiment, heifers in thetwo ECP groups received ECP in conjunction with the CIDR insert. The CIDRinsert was removed and PGF was administered on either d 7 or 9. Heifersreceived ECP 24 h after CIDR removal and were inseminated 30 h after ECP.Heifers in the two GnRH groups received GnRH in conjunction with the CIDRinsert. Heifers received PGF on either d 6 or 7, and the CIDR insert wasremoved on d 7. Heifers were inseminated and received GnRH 48 h after CIDRremoval. Pregnancy rates to FTAI were higher for heifers treated with GnRH.Pregnancy rate to FTAI was highest for heifers in the GnRH group that receivedPGF on d 6 and was lowest for the group that received ECP in combination witha 7-d CIDR insert. In the second experiment, heifers received GnRH in conjunction with theCIDR insert. CIDR inserts were removed and PGF was administered on d 7.Heifers were inseminated 60 h later, with one group receiving GnRH atinsemination. Pregnancy rate to FTAI was higher for heifers that received GnRHat insemination.The final experiment tested the efficacy of estradiol 17_ (E17) or GnRH incombination with a CIDR insert on pregnancy rate to FTAI in Brahman cows.Either E17 or GnRH was administered in conjunction with the CIDR insert.CIDR inserts were removed on d 7. Cows in the GnRH group received PGF ond 6 and GnRH at insemination which occurred 48 h after CIDR removal. Cowsin the E17 group received PGF on d 7, E17 24 h later, and were inseminated 30h after E17 administration. Pregnancy rate to FTAI was higher for cows treatedwith E17.These data indicate acceptable pregnancy rates were obtained when theCIDR insert was combined with either GnRH in beef heifers or with E17 inBrahman cows.