title: Effect of day of the estrous cycle at the initiation of a timed artificial insemination protocol on reproductive responses in dairy heifers.
abstract: Our objectives were to identify stages of the estrous cycle at which initiation of a timed artificial insemination (Ovsynch/TAI) protocol may reduce pregnancy rates and to monitor ovarian follicle dynamics and corpus luteum development after initiation of the Ovsynch/TAI protocol at different stages of the cycle. Cycling Holstein heifers (n = 24) were injected twice with prostaglandin F2alpha to induce estrus and were scanned by ovarian ultrasonography to determine the day of ovulation (d 0). Heifers were assigned to initiate the Ovsynch/TAI protocol at d 2 (n = 5), 5 (n = 5), 10 (n = 4), 15 (n = 5), or 18 (n = 5) of the cycle. The Ovsynch/TAI was initiated with an injection of gonadotropin-releasing hormone agonist followed 7 d later with an injection of prostaglandin F2alpha. At 36 h after injection of prostaglandin F2alpha, heifers were injected with gonadotropin-releasing hormone agonist and inseminated 16 h later. Heifers were scanned daily during the Ovsynch/TAI protocol and every other day after insemination until 16 d later. Blood samples were collected daily starting at the 1st day heifers were scanned and continued until 16 d after insemination. Initiation of the Ovsynch/TAI protocol at d 15 of the estrous cycle caused heifers to ovulate prior to insemination. A shortened return to estrus (< 16 d) was caused by ovulation failure to the second gonadotropin-releasing hormone injection, by incomplete regression of the corpus luteum, and by short life-span of the induced corpus luteum. Day of the cycle in which the Ovsynch/TAI protocol is initiated affects dynamics of follicular development, plasma progesterone profiles, and occurrence of premature ovulation. Size of the pre-ovulatory follicle was associated positively with subsequent progesterone concentrations following insemination.
authors.affiliation: Department of Dairy and Poultry Sciences, University of Florida, Gainesville 32611-0920, USA.
authors.forename: F
authors.initials: F
authors.lastname: Moreira
authors.forename: R L
authors.initials: RL
authors.lastname: de la Sota
authors.forename: T
authors.initials: T
authors.lastname: Diaz
authors.forename: W W
authors.initials: WW
authors.lastname: Thatcher
mesh_terms: D000818:Animals; D002064:Buserelin / Q000494:pharmacology; D002417:Cattle / Q000502:physiology*; D003612:Dairying / Q000379:methods*; D015237:Dinoprost / Q000494:pharmacology; D004971:Estrus / Q000502:physiology*; D004973:Estrus Synchronization; D005260:Female; D005300:Fertility Agents, Female / Q000494:pharmacology; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D006080:Ovarian Follicle / Q000502:physiology; D011247:Pregnancy; D011374:Progesterone / Q000097:blood; D013997:Time Factors
chemical_list: D005300:Fertility Agents, Female; D011374:Progesterone; D015237:Dinoprost; D002064:Buserelin