title: Delayed insemination of nonestrous cows improves pregnancy rates when using sex-sorted semen in timed artificial insemination of suckled beef cows.
abstract: This experiment was designed to test the hypothesis that delayed insemination of nonestrous cows would increase pregnancy rates when using sex-sorted semen in conjunction with fixed-time artificial insemination (FTAI). Estrus was synchronized for 656 suckled beef cows with the 7-d CO-Synch + controlled internal drug release (CIDR) protocol (100 μg GnRH + CIDR [1.38 g progesterone] on d 0, 25 mg PGF2α at CIDR removal on d 7, and 100 μg GnRH on d 10, 66 h after CIDR removal). Estrus detection aids (Estrotect) were applied at PGF2α and CIDR removal on d 7, and estrous expression was recorded at GnRH on d 10. Cows were assigned to 1 of 3 treatments: 1) FTAI (concurrent with GnRH, 66 h after CIDR removal) with conventional semen regardless of estrous expression, 2) FTAI with sex-sorted semen regardless of estrous expression, or 3) FTAI with sex-sorted semen for cows having expressed estrus and delayed AI 20 h after final GnRH for cows failing to express estrus. A treatment × estrous expression interaction was found (P < 0.0001). Higher pregnancy rates (P < 0.0001) were achieved with conventional semen (Treatment 1; 77%) than with sex-sorted semen (Treatments 2 and 3; 51 and 42%, respectively) among cows that expressed estrus. However, among cows that failed to express estrus, delayed insemination with sex-sorted semen yielded higher (P < 0.0001) pregnancy rates than with sex-sorted semen at the standard time (Treatments 2 and 3; 3 versus 36%, respectively). Furthermore, among cows that failed to express estrus, FTAI pregnancy rates when using sex-sorted semen at the delayed time (36%) were comparable (P = 0.9) to those achieved using conventional semen at the standard time (Treatment 1; 37%). These results indicate that delaying AI of nonestrous cows by 20 h from the standard FTAI improves pregnancy rates when sex-sorted semen is used with FTAI.
authors.affiliation: Division of Animal Sciences, University of Missouri, Columbia 65211.
authors.forename: J M
authors.initials: JM
authors.lastname: Thomas
authors.forename: S L
authors.initials: SL
authors.lastname: Lock
authors.forename: S E
authors.initials: SE
authors.lastname: Poock
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: D000818:Animals; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost; D004973:Estrus Synchronization / Q000379:methods; D005260:Female; D007987:Gonadotropin-Releasing Hormone; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D011247:Pregnancy; D018873:Pregnancy Rate; D012661:Semen / Q000502:physiology*; D012743:Sex Preselection / Q000662:veterinary*
chemical_list: D007987:Gonadotropin-Releasing Hormone; D015237:Dinoprost