title: Evaluation of gonadotropin-releasing hormone hydrogen chloride at 3 doses with prostaglandin F2α for fixed-time artificial insemination in dairy cows.
abstract: The objectives of the current study were to evaluate the efficacy and field safety of GnRH HCl administered at 3 doses in fixed-time artificial insemination (FTAI) programs (Ovsynch) in dairy cows. A common protocol was conducted at 6 commercial dairies. Between 188 and 195 cows were enrolled at each site (total enrolled = 1,142). Cows had body condition scores ≥ 2 and ≤ 4, were between 32 to 140 d in milk, and were clinically healthy. Within pen and enrollment day (enrollment cohort), cows were assigned randomly in blocks of 4 to each of 4 treatments: (1) 25mg of PGF2α on d 7 with FTAI 72 ± 2 h later (control); (2) 100 μg of GnRH on d 0, d 7 a dose of 25mg of PGF2α, and the second administration of 100 μg of GnRH (T100) administered either at 48 ± 2 h (d 9) after PGF2α with FTAI 24 ± 2 h later or 56 ± 2 h (d 9) after PGF2α and FTAI 17 ± 2 h later; (3) same as T100 with both injections of 150 μg of GnRH (T150); and (4) same as T100 with both injections of 200 μg of GnRH (T200). Three sites selected the first option and 3 sites selected the second option for the timing of the second injection of all doses of GnRH. Cows were observed daily for signs of estrus and adverse clinical signs. Cows not returning to estrus had pregnancy diagnosis between 42 and 65 d following FTAI. Pregnancies per FTAI (P/FTAI) were analyzed as a binary variable (1 = pregnant, 0 = not pregnant) using a generalized linear mixed model with a binomial error distribution and a logit link function. The statistical model included fixed effects for treatment, random effects of site, site by treatment, enrollment cohort within site, and residual. Parity (first vs. second or greater) was included as a covariate. For demonstration of effectiveness, α=0.05 and a 2-tailed test were used. Fifty-two cows were removed from the study because of either deviation from the protocol, injury, illness, culling, or death. Among the remaining 1,090 cows, 33.9% were primiparous and 66.1% were multiparous. Back-transformed least squares means for P/FTAI were 17.1, 27.3, 29.1, and 32.2% for control, T100, T150 and T200, respectively. The P/FTAI for each GnRH dose differed from that of the control. No differences were detected in P/FTAI between GnRH doses. No treatment-related adverse events were observed. Mastitis was the most frequently observed adverse clinical sign, followed by lameness and pneumonia. This study documents the efficacy and safety of doses of 100 to 200 μg of GnRH as the HCl salt when used in Ovsynch programs.
authors.affiliation: Veterinary Medicine Research and Development, Zoetis Inc., Kalamazoo, MI 49007.
authors.forename: J R
authors.initials: JR
authors.lastname: Chenault
authors.affiliation: Veterinary Medicine Research and Development, Zoetis Inc., Kalamazoo, MI 49007.
authors.forename: D M
authors.initials: DM
authors.lastname: Meeuwse
authors.affiliation: Veterinary Medicine Research and Development, Zoetis Inc., Kalamazoo, MI 49007.
authors.forename: C
authors.initials: C
authors.lastname: LaGrow
authors.affiliation: Veterinary Medicine Research and Development, Zoetis Inc., Kalamazoo, MI 49007.
authors.forename: J-K S
authors.initials: JK
authors.lastname: Tena
authors.affiliation: Veterinary Medicine Research and Development, Zoetis Inc., Kalamazoo, MI 49007.
authors.forename: S L
authors.initials: SL
authors.lastname: Wood-Follis
authors.affiliation: Veterinary Medicine Research and Development, Zoetis Inc., Kalamazoo, MI 49007. Electronic address: John.W.Hallberg@zoetis.com.
authors.forename: J W
authors.initials: JW
authors.lastname: Hallberg
mesh_terms: D000818:Animals; D002417:Cattle / Q000502:physiology*; D015237:Dinoprost / Q000008:administration & dosage*; D004971:Estrus; D004973:Estrus Synchronization; D005260:Female; D007987:Gonadotropin-Releasing Hormone / Q000008:administration & dosage*; D007315:Insemination, Artificial / Q000662:veterinary*; D007774:Lactation; D008892:Milk / Q000378:metabolism; D010298:Parity; D011247:Pregnancy; D011897:Random Allocation; D013997:Time Factors
chemical_list: D007987:Gonadotropin-Releasing Hormone; D015237:Dinoprost
keywords: Ovsynch; dairy cow; fixed-time artificial insemination; gonadotropin-releasing hormone (GnRH)