title: Effects of presynchronization and length of proestrus on fertility of grazing dairy cows subjected to a 5-day timed artificial insemination protocol.
abstract: The objectives were to compare the effects of 2 methods of presynchronization and 2 lengths of proestrus on fertility of grazing dairy cows subjected to a 5-d timed artificial insemination (AI) protocol at initiation of breeding season. Lactating dairy cows (n=1,754) from 3 seasonal grazing farms were blocked within farm by breed, parity, and days in milk (DIM). Study d 0 was considered the day of AI of cows in COS72 (72h of proestrus). Within each block, cows were randomly assigned to 1 of 2 presynchronization treatments: a PGF(2α)-based program, Presynch, consisting of 2 injections of PGF(2α) administered on d -32 and -18, or a PGF(2α)-GnRH-based program, Double-Ovsynch (DO), consisting of GnRH on d -25, PGF(2α) on d -18, and GnRH on d -15. Within each of the 2 presynchronization treatments, cows were randomly assigned to 1 of 2 lengths of proestrus within the 5-d timed AI protocol, consisting of GnRH on d -8, PGF(2α) on d -3 and -2, and GnRH+AI at either 58 h (COS58) or 72 h (COS72) after the d -3 PGF(2α) injection. Ovaries were scanned by ultrasonography twice, on d -42 and -32, to determine estrous cyclicity before enrollment in the study. Blood was sampled and analyzed for concentrations of estradiol on the day of AI. Pregnancies per AI (P/AI) were determined 30 and 65 d after AI. Presynchronization did not affect the concentration of estradiol at AI (DO=6.4 vs. Presynch=5.8 pg/mL), detection of estrus at AI (20.8 vs. 25.9%), or P/AI on d 30 (56.8 vs. 59.1%) and 65 (52.5 vs. 52.4%) after the first AI. Cows receiving COS72 had increased concentration of estradiol (6.6 vs. 5.5 pg/mL) and detection of estrus at AI (28.5 vs. 10.8%) compared with cows receiving COS58. Length of proestrus did not affect P/AI on d 30 (COS72=58.7 vs. COS58=56.1%) but, in Presynch cows, COS58 was detrimental to fertility on d 65 after AI (54.9 vs. 46.5%). Pregnancy loss between gestational d 30 and 65 was greater for Presynch than for DO (7.6 vs. 11.3%), but it was not affected by length of proestrus. Estrous cyclic cows had greater P/AI than anovular cows on d 30 (61.7 vs. 35.1%) and 65 (56.1 vs. 30.7%), but no interaction between estrous cyclic status and treatments was detected. Crossbred Holstein/Jersey cows had superior fertility than their purebred counterparts during the breeding season. The Presynch and DO protocols resulted in similar fertility with no overall difference between the presynchronization methods; however, limiting the length of proestrus to 58 h reduced P/AI in the 5-d timed AI protocol when cows had their estrous cycle presynchronized with Presynch but not with DO.
authors.affiliation: Department of Animal Sciences, University of Florida, Gainesville, Florida 32611, USA.
authors.forename: E S
authors.initials: ES
authors.lastname: Ribeiro
authors.forename: A P A
authors.initials: AP
authors.lastname: Monteiro
authors.forename: F S
authors.initials: FS
authors.lastname: Lima
authors.forename: H
authors.initials: H
authors.lastname: Ayres
authors.forename: R S
authors.initials: RS
authors.lastname: Bisinotto
authors.forename: M
authors.initials: M
authors.lastname: Favoreto
authors.forename: L F
authors.initials: LF
authors.lastname: Greco
authors.forename: R S
authors.initials: RS
authors.lastname: Marsola
authors.forename: W W
authors.initials: WW
authors.lastname: Thatcher
authors.forename: J E P
authors.initials: JE
authors.lastname: Santos
mesh_terms: D000818:Animals; D002417:Cattle; D003612:Dairying / Q000379:methods; D004958:Estradiol / Q000097:blood; D004973:Estrus Synchronization / Q000379:methods*; D005260:Female; D005298:Fertility / Q000502:physiology; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D011247:Pregnancy; D011359:Proestrus / Q000502:physiology*; D013997:Time Factors
chemical_list: D004958:Estradiol