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Effect of a high dose of gonadorelin hydrochloride at the first gonadotropin-releasing hormone of the breeding-Ovsynch of a fertility program on ovulation rate and pregnancies per AI in first-service lactating Holstein cows.

T. Valdes Arciniega

Abstract:

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Effect of a high dose of gonadorelin hydrochloride at the first gonadotropin-releasing hormone of the breeding-Ovsynch of a fertility program on ovulation rate and pregnancies per AI in first-service lactating Holstein cows.
T. Valdes Arciniega*1, I. M. R. Le�o1, E. Anta Galvan1, T. O. Cunha1, M. S. El Azzi1,2, N. B. Cook1, J. P. N. Martins1. 1School of Veterinary Medicine, University of Wisconsin-Madison Madison, WI, 2Universidade Federal de Lavras Lavras, MG, Brazil.

The aim of the present study was to determine if a high dose of gonadorelin hydrochloride (GnRH, 200 �g; Factrel, Zoetis) i.m. would increase ovulation rate compared with a low dose (100 �g) i.m. at the first GnRH of the breeding-Ovsynch (G1), and thereby increase first service pregnancies per AI (P/AI) in lactating Holstein cows. Weekly cohorts of cows (n = 765) from a commercial dairy farm were randomly assigned according to ending ear tag number (odd or even) to receive either a low or a high dose of GnRH at G1 of the Double-Ovsynch program (GnRH — 7d — PGF — 3d — GnRH — 7d — GnRH (G1) — 7d — PGF — 1d — PGF — 32h — GnRH — 16h — TAI). Primiparous (n = 240) and multiparous (n = 525) cows received treatments at 72 � 3 and 62 � 3 DIM, respectively. Ovulation was determined by the disappearance of a follicle with diameter = 9 mm, and the appearance of a luteal structure between the d of treatment and 2 d later by ultrasound. Cows received timed-AI using either conventional Angus (n = 124) or Holstein (n = 468) semen. Pregnancy diagnosis was performed by farm veterinarians using ultrasound at 32 d post-AI. Data were analyzed by logistic regression using Proc GLIMMIX of SAS. The model included fixed effects of treatment, parity and the interaction of treatment � parity. High dose increased (P < 0.01) ovulation rates in both primiparous (78.6 vs. 61.9%) and multiparous (84.8 vs. 70.5%) cows compared with the low dose treatment. Multiparous cows also had greater (P = 0.03) overall ovulation rate than primiparous cows (77.5 vs. 71.2%). The high dose did not have a significant effect on P/AI in primiparous (64.9 vs. 55.4%; P = 0.27) and in multiparous (47.1 vs. 44.8%; P = 0.62) cows, compared with the low dose treatment. Overall P/AI was greater for primiparous compared with multiparous cows (60.8 vs. 45.9%; P < 0.01). In summary, increasing the dose of GnRH treatment at G1 of the Double-Ovsynch program increased ovulation rate, but it did not significantly improve P/AI in first service lactating Holstein cows, based on preliminary data.

Keywords: GnRH, ovulation, Double-Ovsynch.