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Association between age at first calving and reproductive performance of primiparous cows managed with a program that favored insemination at detected estrus.

E. Sitko

Events

06-23-2020

Abstract:

243
Association between age at first calving and reproductive performance of primiparous cows managed with a program that favored insemination at detected estrus.
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 Holstein cows submitted to AI with a program that favored insemination at detected estrus (AIE). Within farm (n = 5), cows (n = 1,163) were retrospectively grouped by AFC in mo (n; mean; range): low (n = 373; 21.4; 20.3—22.4), medium (n = 421; 22.1; 21.3—23.3), and high (n = 369, 23.5; 21.9—29.7). Cows were eligible for AIE after a PGF2α (PGF) treatment at 53 � 3 DIM. Cows not AIE by 74 � 3 DIM received timed AI after GnRH, 7 d PGF, 1 d PGF, 32 h GnRH, 18 h TAI with progesterone supplementation from the first GnRH to PGF. Thereafter, cows were AIE up to the time of nonpregnancy diagnosis at 32 � 3 d after AI. Nonpregnant cows received the same protocol for TAI than for first AI. Binomial data were analyzed by logistic regression. Time to pregnancy and herd exit up to 200 DIM by Cox's proportional hazard regression. AFC group (AFCG) was included as fixed and farm as random effect. Confounders included season (cold vs. warm), AI type (TAI vs. AIE), milk production group (MLKG; low, medium, and high), and daughter pregnancy rate group (DPRG; low, medium, and high). The proportion of cows AIE for first AI, was affected by DPRG and AFCG (P < 0.05), whereby it was greater for low (76.0%) and medium AFC (73.9%) than for high AFC (67.0%). First AI pregnancy per AI (P/AI), was affected by DPRG and the interaction between AI type and AFCG (P < 0.05). Within high AFC, P/AI was greater for TAI (59.2%) than for AIE (39.3%), whereas it was similar within medium and low AFC groups. Time to pregnancy was affected by DPRG (P < 0.05) but not AFCG (P > 0.05). The proportion of cows pregnant up to 200 DIM was not affected by AFCG (P > 0.05). MLKG (P < 0.01) but not AFCG (P > 0.05) affected the hazard of herd exit up to 200 DIM. In conclusion, AFC affected the proportion of primiparous cows AIE for first AI and first service P/AI, but did not affect the pregnancy and herd exit dynamics up to 200 DIM for cows managed with a program that favored insemination at detected estrus rather than TAI.

Keywords: first calving, fertility, estrus.

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.