title: Development of a progestin-based estrus synchronization program: II. Reproductive response of cows fed melengestrol acetate for 14 days with injections of progesterone and prostaglandin F2alpha.
abstract: We tested the efficacy of an estrus control system designed to provide optimal control of follicular development. In Exp. 1, postpartum cows (n = 133) and yearling heifers (n = 57) were fed either .5 mg x female(-1) x d(-1) of melengestrol acetate (MGA) or the carrier for MGA from d -13 to d 0 (d 0 = last day of MGA feeding). All females received 25 mg of PGF2alpha (i.m.) on d -13 and 0. On d -6, cows and heifers fed MGA were administered an i.m. injection of progesterone (200 mg; MGA/P4), and those fed the corn carrier (2XPGF2alpha) received no progesterone. Beginning on d 1, females were bred by AI from d 1 to at least d 5. During the estrus synchronization period (d 1 to d 5), more (P < .05) postpartum cows were observed in estrus (70.1 vs 42.4%), the timing of estrus was more (P < .05) precise, conception rate was similar, and pregnancy rate was higher (P < .05) in the MGA/P4 than in the 2XPGF2alpha treatment. More (P < .05) cows that were anestrous at the beginning of the breeding season were in estrus during the synchronization period in the MGA/P4 (55.8%) than in the 2XPGF2alpha (28.6%) treatment. In heifers, estrus was synchronized in over 90% of females, and neither conception nor pregnancy rate during the synchronization period differed between treatments. In Exp. 2, postpartum cows (n = 122) and heifers (n = 84) received treatments (MGA/P4 or 2XPGF2alpha) as described for Exp. 1 with one exception. In the MGA/ P4 treatment, progesterone was administered on d -7 rather than d -6. Females were bred by AI from d 1 to 5. The estrus response and conception rate during the synchronization period did not differ between treatments for either cows or heifers. We conclude that the progestin-based estrous synchronization system used in this study effectively synchronized an estrus of normal fertility in cyclic cows and induced a majority of anestrous cows to reinitiate estrous cycles.
authors.affiliation: Department of Animal Sciences, The Ohio State University, Columbus 43210, USA.
authors.forename: C M
authors.initials: CM
authors.lastname: McDowell
authors.forename: L H
authors.initials: LH
authors.lastname: Anderson
authors.forename: R P
authors.initials: RP
authors.lastname: Lemenager
authors.forename: D A
authors.initials: DA
authors.lastname: Mangione
authors.forename: M L
authors.initials: ML
authors.lastname: Day
mesh_terms: D000284:Administration, Oral; D000821:Animal Feed; D000818:Animals; D002417:Cattle / Q000502:physiology*; D019587:Dietary Supplements; D015237:Dinoprost / Q000008:administration & dosage / Q000494:pharmacology*; D004973:Estrus Synchronization / Q000187:drug effects*; D005260:Female; D005306:Fertilization / Q000187:drug effects; D007273:Injections, Intramuscular / Q000662:veterinary; D007315:Insemination, Artificial / Q000662:veterinary; D008552:Melengestrol Acetate / Q000008:administration & dosage / Q000494:pharmacology*; D049590:Postpartum Period / Q000187:drug effects; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000008:administration & dosage / Q000097:blood / Q000494:pharmacology*; D045167:Progesterone Congeners / Q000008:administration & dosage / Q000494:pharmacology*
chemical_list: D045167:Progesterone Congeners; D011374:Progesterone; D008552:Melengestrol Acetate; D015237:Dinoprost