title: Reducing the interval from presynchronization to initiation of timed artificial insemination improves fertility in dairy cows.
abstract: The objective was to determine if reducing the interval from presynchronization to the first GnRH injection (G1) of a timed artificial insemination (AI) protocol improves pregnancy per AI. One thousand two hundred fourteen Holstein cows, at 37 +/- 3 d in milk (DIM), were stratified by parity, DIM, and milk yield in the first month postpartum and randomly assigned to control (n = 412), 2 injections of PGF2alpha at 37 +/- 3 and 51 +/- 3 DIM, then enrolled in a timed AI protocol 14 d later; PShort (n = 410), 2 injections of PGF2alpha at 40 +/- 3 and 54 +/- 3 DIM, then enrolled in a timed AI protocol 11 d later; or PShortG (n = 392), same as PShort, but with an injection of GnRH 7 d before G1. All cows received the same timed AI protocol (d 65, G1; d 72, PGF2alpha; d 73, 1 mg of estradiol cypionate; d 75, AI). A subset of 1,000 cows had their ovaries examined by ultrasonography at G1 and 7 d later when PGF2alpha of the timed AI was given to determine presence of corpus luteum (CL) and ovulation to G1. Pregnancy was diagnosed on d 38 after timed AI, and pregnant cows were reevaluated for pregnancy 4 wk later. Altering the interval between presynchronization and G1 did not affect the proportion of cows with a CL at G1, but GnRH 7 d before G1 increased the proportion of cows with a CL. Ovulation to G1 was greater for 11 compared with the 14 d interval, but GnRH did not improve ovulation. The increased ovulation to G1 when the interval was reduced from 14 to 11 d was observed only in cows with a CL at G1, but treatment did not affect ovulation in cows without a CL at G1. Treatment affected the pregnancy per AI on d 38 and 66 after insemination, and they were greater for the 11 compared with 14-d interval, but addition of GnRH did not improve pregnancy per AI. Cows ovulating to G1 had greater pregnancy per AI regardless of whether or not they had a CL at G1. Reducing the interval from presynchronization to initiation of the timed AI protocol from 14 to 11 d increased ovulation to G1 and pregnancy per AI in lactating dairy cows.
authors: Veterinary Medicine Teaching and Research Center, University of California-Davis, Tulare 93274, USA.
authors: K N
authors: KN
authors: Galvão
authors: M F
authors: MF
authors: Sá Filho
authors: J E P
authors: JE
authors: Santos
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost / Q000008:administration & dosage; D004958:Estradiol / Q000008:administration & dosage / Q000031:analogs & derivatives; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D005298:Fertility; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D007774:Lactation; D010053:Ovary / Q000000981:diagnostic imaging; D010060:Ovulation; D010298:Parity; D011247:Pregnancy; D013997:Time Factors; D014463:Ultrasonography
chemical_list: D007987:Gonadotropin-Releasing Hormone; D004958:Estradiol; C007630:estradiol 17 beta-cypionate; D015237:Dinoprost