title: Synchronization of estrus in beef heifers using either melengesterol acetate (MGA)/prostaglandin or MGA/Select Synch.
abstract: The objective of this study was to evaluate synchronization, conception, and pregnancy rates of yearling beef heifers synchronized with either the Select Synch protocol preceded by 7 days of MGA feeding (MGA/Select Synch) or the traditional MGA/PGF protocol. Heifers in the MGA/Select Synch group (n = 402) were fed MGA (0.5 mg/day/head) for 7 days, received an injection of GnRH (100 microg) the day following the last MGA feeding and an injection of PGF (25 mg) 7 days after GnRH. Heifers in the MGA/PGF group (n = 394) received MGA (0.5 mg/day/head) for 14 days, followed by an injection of PGF (25 mg) 17 days later. Synchronization rates tended (P = 0.08) to be higher for the MGA/Select Synch (82%) compared to the MGA/PGF (77%)-treated heifers. Conception and pregnancy rates to AI were similar (P > 0.10), 57 and 46% for the MGA/Select Synch heifers and 61 and 47% for the MGA/PGF heifers, respectively. Mean estrous response (h) was earlier (P < 0.05) for the MGA/Select Synch versus MGA/PGF treatment, 56 versus 61 h post-PGF treatment, respectively. In summary, short-term (7 days) MGA feeding preceding the Select Synch protocol produced similar synchronization, conception, and pregnancy rates as the traditional MGA/PGF protocol.
authors.affiliation: Montana State University, Bozeman, USA. rick@larrl.ars.usda.gov
authors.forename: R N
authors.initials: RN
authors.lastname: Funston
authors.forename: R P
authors.initials: RP
authors.lastname: Ansotegui
authors.forename: R J
authors.initials: RJ
authors.lastname: Lipsey
authors.forename: T W
authors.initials: TW
authors.lastname: Geary
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004032:Diet; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage*; D007315:Insemination, Artificial / Q000662:veterinary; D008552:Melengestrol Acetate / Q000008:administration & dosage*; D011247:Pregnancy; D045167:Progesterone Congeners / Q000008:administration & dosage*; D011460:Prostaglandins F / Q000008:administration & dosage*; D013997:Time Factors
chemical_list: D045167:Progesterone Congeners; D011460:Prostaglandins F; D007987:Gonadotropin-Releasing Hormone; D008552:Melengestrol Acetate