title: Estrus synchronization of beef cattle with a combination of melengestrol acetate and an injection of progesterone and 17beta-estradiol.
abstract: Our hypothesis was that estrus synchronization in beef cattle using melengestrol acetate (MGA) and an injection of progesterone (P4) and 17beta-estradiol (E2) to regress dominant ovarian follicles would improve pregnancy rate (number conceived/number in group) to AI compared with feeding only MGA or injecting PGF2alpha. During 2 yr, peripubertal heifers (n = 52) and cows (n = 327) received either 1) MGA for 18 d (d 0 = 1st d of MGA) plus an injection of P4 and E2 in sesame oil (vehicle) on d 11 to regress persistent ovarian follicles (MGA+P4), 2) MGA for 18 d plus vehicle on d 11 (MGA), or 3) two injections of PGF2alpha 10 d apart (d 7 and 17, PG). Concentration of P4 was assessed in blood samples obtained on d 0, 7, and 17 to indicate estrual status (anestrual or estrual) during treatment to induce estrus synchrony. Observations for detection of estrus occurred every 6 h for 180 h following treatment cessation. Females showing estrus were inseminated 6 to 12 h after estrus detection. Conception to AI was determined by ultrasonography 35 to 40 d later. Conception rate was greater (P < .05) in females in the PG than in those in the MGA group but did not differ from conception rate of females in the MGA+P4 group. Among anestrual females, estrus synchrony rates were greatest (P < .10) among females treated with MGA+P4. Among females that were estrual before treatment cessation, estrus synchrony rates were greater (P < .10) among females treated with MGA+P4 or PG than among those given MGA. Pregnancy rates were greater (P < .05) among females that were anestrual before treatment cessation and treated with MGA or MGA+P4 than among those treated with PG. Estrus synchronization using MGA+P4 and E2 differentially improves estrus synchronization and pregnancy rates among anestrual and estrual beef cattle while maintaining conception rates similar to those of PGF2alpha-treated females.
authors.affiliation: Department of Animal Science, University of Nebraska, Lincoln 68583-0908, USA.
authors.forename: K E
authors.initials: KE
authors.lastname: Fike
authors.forename: M E
authors.initials: ME
authors.lastname: Wehrman
authors.forename: B R
authors.initials: BR
authors.lastname: Lindsey
authors.forename: E G
authors.initials: EG
authors.lastname: Bergfeld
authors.forename: E J
authors.initials: EJ
authors.lastname: Melvin
authors.forename: J A
authors.initials: JA
authors.lastname: Quintal
authors.forename: E L
authors.initials: EL
authors.lastname: Zanella
authors.forename: F N
authors.initials: FN
authors.lastname: Kojima
authors.forename: J E
authors.initials: JE
authors.lastname: Kinder
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D004338:Drug Combinations; D004958:Estradiol / Q000097:blood / Q000494:pharmacology*; D004973:Estrus Synchronization / Q000187:drug effects*; D005260:Female; D007315:Insemination, Artificial / Q000662:veterinary; D008552:Melengestrol Acetate / Q000494:pharmacology*; D006080:Ovarian Follicle / Q000187:drug effects; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000494:pharmacology*; D045167:Progesterone Congeners / Q000494:pharmacology*
chemical_list: D004338:Drug Combinations; D045167:Progesterone Congeners; D011374:Progesterone; D004958:Estradiol; D008552:Melengestrol Acetate