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Age at first calving affected reproductive performance of primiparous cows managed with a program that favored timed artificial insemination.

E. Sitko

Events

06-23-2020

Abstract:

244
Age at first calving affected reproductive performance of primiparous cows managed with a program that favored timed artificial insemination.
E. Sitko*, M. M. P�rez, M. Masello, G. E. Granados, J. O. Giordano. Department of Animal Science, Cornell University Ithaca, NY.

Our objective was to evaluate the effect of age at first calving (AFC) on reproductive performance and herd exit of primiparous lactating Holstein cows submitted for AI with a program that favored timed AI (TAI). Within farm (n = 5), cows (n = 1,072) were retrospectively grouped by AFC in mo (n; mean; range): low (n = 323; 21.5; 18.6—22.4), medium (n = 394; 22.1; 21.3—23.3), and high (n = 355, 23.5; 21.8—29.6). AFC differences were the outcome of different reproductive performance as heifers. First service TAI was at 84 � 3 DIM after Double-Ovsynch [GnRH, 7 d PGF (PGF), 3 d GnRH, 7 d GnRH, 7 d PGF, 1 d PGF, 32 h GnRH, 18 h TAI]. Thereafter, cows received AI at detected estrus (AIE) any time or TAI if not AIE up to the time of nonpregnancy diagnosis at 32 � 3 d after AI. Nonpregnant cows with a corpus luteum (CL) received: GnRH 25 � 3 d after AI, 7 d PGF, 1 d PGF, 32 h GnRH, 18 h TAI. Cows with NoCL received GnRH 25 � 3 and 32 � 3 d after AI, 7 d PGF, 1 d PGF, 32 h GnRH, 18 h TAI with progesterone supplementation. Binomial data were analyzed by logistic regression. Time to pregnancy and herd exit up to 200 DIM were analyzed by Cox's regression. AFC group (AFCG) was included as fixed and farm as random effect. Confounders included season (cold vs. warm), milk production group (MLKG; low, medium, and high), and daughter pregnancy rate group (DPRG; low, medium, and high). First AI P/AI, was affected by DPRG (P < 0.01), but not AFCG (P > 0.05). Time to pregnancy was affected by DPRG (P < 0.05) and tended to be affected by AFCG (P = 0.06), whereby the hazard of pregnancy (HR; 95% CI) was greater for low than for high (1.21; 1.04—1.42) AFC, and for medium than high AFC (1.12; 1.01—1.25) but was similar for low and medium AFC (1.01; 0.91—1.12). More (P < 0.05) cows were pregnant by 200 DIM in the low (93.5%) than high (87.9%) AFC group, whereas the medium (91.6%) group was intermediate. MLKG (P < 0.01) but not AFCG (P > 0.05) affected the hazard of herd exit. We conclude that AFC affected the reproductive performance of primiparous lactating Holstein cows managed with a program that favored TAI because cows with reduced AFC had improved reproductive performance. Also, AFC did not affect the herd exit dynamics.

Keywords: age at first calving, fertility, timed AI.

Biography: Emily Sitko obtained her Bachelor of Science in animal science from Cornell University in 2017. She began her PhD program in 2017 at Cornell University's Department of Animal Science working with Julio Giordano's laboratory. Her research is focused in dairy cattle reproductive physiology and management.