title: Resynchronization strategies to improve fertility in lactating dairy cows utilizing a presynchronization injection of GnRH or supplemental progesterone: I. Pregnancy rates and ovarian responses.
abstract: Objectives were to evaluate 3 resynchronization protocols for lactating dairy cows. At 32+/-3 d after pre-enrollment artificial insemination (AI; study d -7), 1 wk before pregnancy diagnosis, cows from 2 farms were enrolled and randomly assigned to 1 of 3 resynchronization protocols after balancing for parity, days in milk, and number of previous AI. All cows were examined for pregnancy at 39+/-3 d after pre-enrollment AI (study d 0). Cows enrolled as controls (n=386) diagnosed not pregnant were submitted to a resynchronization protocol (d 0-GnRH, d 7-PGF2alpha, and d 10-GnRH and AI) on the same day. Cows enrolled in the GGPG (GnRH-GnRH-PGF2alpha-GnRH) treatment (n=357) received a GnRH injection at enrollment (d -7) and if diagnosed not pregnant were submitted to the resynchronization protocol for control cows on d 0. Cows enrolled in CIDR treatment (n=316) diagnosed not pregnant received the resynchronization protocol described for control cows with addition of a controlled internal drug release (CIDR) insert containing progesterone (P4) from d 0 to 7. In a subgroup of cows, ovaries were scanned and blood was sampled for P4 concentration on d 0 and 7. After resynchronized AI, cows were diagnosed for pregnancy at 39+/-3 and 67+/-3 d (California herds) or 120+/-3 d (Arizona herds). Cows in the GGPG treatment had more corpora lutea than CIDR and control cows on d 0 (1.30+/-0.11, 1.05+/-0.11, and 1.05+/-0.11, respectively) and d 7 (1.41+/-0.14, 0.97+/-0.13, and 1.03+/-0.14, respectively). A greater percentage of GGPG cows ovulated to GnRH given on d 0 compared with CIDR and control cows (48.4, 29.6, and 36.6%, respectively), but CIDR and control did not differ. At 39+/-3 d after resynchronized AI, pregnancy per AI (P/AI) was increased in GGPG (33.6%) and CIDR (31.3%) cows compared with control (24.6%) cows. At 67 or 120+/-3 d after resynchronized AI, P/AI of GGPG and CIDR cows was increased compared with control cows (31.2, 29.5, and 22.1%, respectively). Presynchronizing the estrous cycle of lactating dairy cows with a GnRH 7 d before the start of the resynchronization protocol or use of a CIDR insert within the resynchronization protocol resulted in greater P/AI after resynchronized AI compared with control cows.
authors: University of Arizona, Department of Animal Sciences, Tucson 85721, USA.
authors: S T
authors: ST
authors: Dewey
authors: L G D
authors: LG
authors: Mendonça
authors: G
authors: G
authors: Lopes
authors: F A
authors: FA
authors: Rivera
authors: F
authors: F
authors: Guagnini
authors: R C
authors: RC
authors: Chebel
authors: T R
authors: TR
authors: Bilby
mesh_terms: D000034:Abortion, Veterinary / Q000503:physiopathology; D000818:Animals; D002417:Cattle; D004973:Estrus Synchronization / Q000379:methods* / Q000502:physiology; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000097:blood / Q000494:pharmacology*; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary; D007774:Lactation / Q000502:physiology; D008892:Milk / Q000378:metabolism; D010053:Ovary / Q000000981:diagnostic imaging / Q000187:drug effects*; D010298:Parity; D011247:Pregnancy; D018873:Pregnancy Rate; D011374:Progesterone / Q000097:blood / Q000494:pharmacology*; D014463:Ultrasonography
chemical_list: D007987:Gonadotropin-Releasing Hormone; D011374:Progesterone