title: Comparison of long-term progestin-based estrus synchronization protocols in beef heifers.
abstract: Two experiments evaluated long-term progestin-based estrus-synchronization programs on the basis of potential for use in facilitating fixed-time AI in estrous cycling and prepubertal beef heifers. In Exp. 1, heifers were assigned to 1 of 2 treatments by age, BW, and estrous cyclicity status. Heifers assigned to the melengestrol acetate-PGF(2α) protocol (MGA-PG; n = 50) received MGA (0.5 mg·animal(-1)·d(-1)) in a 1.0-kg carrier from d 0 to 13 and were administered PGF(2α) (25 mg, intramuscularly) 19 d after MGA withdrawal (d 32). Heifers assigned to the Show-Me-Synch protocol (n = 49) received a controlled internal drug release (CIDR) insert (1.38 g of progesterone) from d 2 to 16 followed by PGF(2α) administration 16 d after CIDR removal (d 32). All heifers were fitted with HeatWatch estrus-detection transmitters at the time of progestin removal for continuous estrus detection through the synchronized period after PGF(2α). In Exp. 2, heifers (n = 396) were assigned to the same 2 treatments described in Exp. 1 by age, BW, and reproductive tract score. Heifers in Exp. 2, however, were fitted with HeatWatch estrus-detection transmitters at PGF(2α) to characterize estrus-distribution patterns during the synchronized period after PGF(2α). Heifers in both experiments were inseminated approximately 12 h after the onset of estrus. In Exp. 1, estrous response after PGF(2α) and mean interval to estrus after PGF(2α) did not differ between MGA-PG and Show-Me-Synch treatments (P = 0.97). The variance for interval to estrus after PGF(2α) tended (P = 0.06) to be reduced among MGA-PG-treated heifers compared with Show-Me-Synch-treated heifers. Conception to AI, AI pregnancy, and final pregnancy rates did not differ (P > 0.1) between treatments. In Exp. 2, estrous response after PGF(2α) was greater (P = 0.01) among Show-Me-Synch-treated heifers (92%) compared with MGA-PG-treated heifers (85%); however, mean interval to estrus after PGF(2α) did not differ (P = 0.74) between MGA-PG (57.4 ± 2.5 h) and Show-Me-Synch (56.2 ± 2.5 h) treatments. The variance for interval to estrus after PGF(2α) was reduced (P < 0.01) among Show-Me-Synch-treated vs. MGA-PG-treated heifers. Conception to AI, AI pregnancy, and final pregnancy rates did not differ (P > 0.1) between treatments. In summary, the Show-Me-Synch protocol compared favorably with the MGA-PG protocol on the basis of estrous response, synchrony of estrus, and resulting fertility after treatment administration.
authors.affiliation: Division of Animal Science, S132 ASRC, University of Missouri, Columbia, 65211, USA.
authors.forename: D A
authors.initials: DA
authors.lastname: Mallory
authors.forename: D J
authors.initials: DJ
authors.lastname: Wilson
authors.forename: D C
authors.initials: DC
authors.lastname: Busch
authors.forename: M R
authors.initials: MR
authors.lastname: Ellersieck
authors.forename: M F
authors.initials: MF
authors.lastname: Smith
authors.forename: D J
authors.initials: DJ
authors.lastname: Patterson
mesh_terms: D000282:Administration, Intravaginal; D000284:Administration, Oral; D000818:Animals; D002417:Cattle; D015237:Dinoprost / Q000008:administration & dosage / Q000494:pharmacology; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D005300:Fertility Agents, Female / Q000008:administration & dosage* / Q000494:pharmacology*; D005306:Fertilization; D007315:Insemination, Artificial; D008552:Melengestrol Acetate / Q000008:administration & dosage / Q000494:pharmacology; D011247:Pregnancy; D011374:Progesterone / Q000008:administration & dosage / Q000494:pharmacology
chemical_list: D005300:Fertility Agents, Female; D011374:Progesterone; D008552:Melengestrol Acetate; D015237:Dinoprost