title: Effects of 21-day treatment with melengestrol acetate (MGA) with or without subsequent prostaglandin F2 alpha on synchronization of estrus and fertility in beef cattle.
abstract: Beef cattle were treated to synchronize estrus using one of three procedures, and effects on subsequent endocrine responses and fertility were studied. Procedures were 1) feeding .5 mg.head-1.d-1 of melengestrol acetate (MGA) for 21 d (M), 2) feeding .5 mg.head-1.d-1 of melengestrol acetate for 21 d followed 14 d later by a single injection of prostaglandin F2 alpha (M + P) and 3) two injections of prostaglandin (PGF) 14 d apart (P). In Exp. 1, 94 beef cows were assigned to be artificially inseminated 12 h after detection of estrus. Procedures for synchronizing estrus did not affect the proportion of cows observed in estrus within 7 d (mean = 70.2%). However, conception rate of cows treated with MGA alone was lower (P less than .01) than that of cows treated with PGF alone (31.8 vs 78.3%). The conception rate of cows in the M + P group was intermediate (57.1%) but greater than that of cows treated with MGA alone (P less than .10). In Exp. 2, 18 heifers were observed for estrus four times daily and bled daily from 1 wk before predicted estrus until second estrus or 35 d post-treatment. Heifers treated with MGA alone maintained lower concentrations of progesterone and higher concentrations of estradiol-17 beta before first estrus than heifers treated with MGA and PGF or PGF alone (P less than .01). Conception rate following insemination was lower after long-term feeding of MGA than after two injections of PGF. Delaying insemination until after a PGF-shortened cycle 14 d after MGA resulted in an intermediate conception rate.(ABSTRACT TRUNCATED AT 250 WORDS)
authors: Dept. Anim. & Dairy Sci., Auburn University, AL 36849.
authors: D A
authors: DA
authors: Coleman
authors: F F
authors: FF
authors: Bartol
authors: M G
authors: MG
authors: Riddell
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost / Q000494:pharmacology*; D004958:Estradiol / Q000097:blood; D004973:Estrus Synchronization / Q000187:drug effects*; D005260:Female; D005298:Fertility / Q000187:drug effects*; D005306:Fertilization / Q000187:drug effects; D008552:Melengestrol Acetate / Q000494:pharmacology*; D011374:Progesterone / Q000097:blood
chemical_list: D011374:Progesterone; D004958:Estradiol; D008552:Melengestrol Acetate; D015237:Dinoprost