title: Synchronization of estrus with melengestrol acetate and prostaglandin F2 alpha in beef and dairy heifers.
abstract: Beef (n = 783) and dairy (n = 209) heifers at 14 locations were used to evaluate the efficacy of feeding melengestrol acetate (MGA; .5 mg/d) for 7 d followed by an i.m. injection of 25 mg prostaglandin F2 alpha (PGF) on the last day of MGA feeding (MGA + PGF) to synchronize estrus. Untreated heifers (C) and heifers injected once i.m. with PGF served as contemporary controls. Heifers were observed for estrual behavior for a minimum of 38 d starting on the 2nd d of MGA feeding. Heifers in estrus from d 1 through d 60 after PGF injection were artificially inseminated (AI) or bred to bulls (d 30 to 60 post PGF only). During the 7-d MGA feeding period fewer (P less than .01) MGA + PGF (1.5%) than C (20.6%) or PGF (18.1%) heifers were observed in estrus. Percent of heifers in estrus d 1 to 6 post PGF was different among groups (P less than .05; 30.5, 52.8, 72.3 for C, PGF and MGA + PGF, respectively). More (P less than .01) MGA-fed (92%) than non-MGA-fed (C and PGF combined) heifers (85.4%) were observed in estrus during d 1 to 24. Conception rate (CR) during d 1 to d 6 was not different (P = .19) between C (58.9%) and MGA + PGF (51.2%) heifers; CR was lower (P = .01) for MGA + PGF than for PGF (68.3%) heifers.(ABSTRACT TRUNCATED AT 250 WORDS)
authors.affiliation: Upjohn Company, Kalamazoo, MI 49001.
authors.forename: J R
authors.initials: JR
authors.lastname: Chenault
authors.forename: J F
authors.initials: JF
authors.lastname: McAllister
authors.forename: C W
authors.initials: CW
authors.lastname: Kasson
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost / Q000494:pharmacology*; D004347:Drug Interactions; D004971:Estrus / Q000187:drug effects; D004973:Estrus Synchronization / Q000187:drug effects*; D005260:Female; D005306:Fertilization; D008552:Melengestrol Acetate / Q000494:pharmacology*; D011245:Pregnadienes / Q000494:pharmacology*; D011897:Random Allocation
chemical_list: D011245:Pregnadienes; D008552:Melengestrol Acetate; D015237:Dinoprost