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Effect of timing of AI using sexed semen relative to induction of ovulation after a Double-Ovsynch protocol on pregnancy outcomes and fetal sex in lactating primiparous Holstein cows.

M. R. Lauber

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06-23-2020

Abstract:

245
Effect of timing of AI using sexed semen relative to induction of ovulation after a Double-Ovsynch protocol on pregnancy outcomes and fetal sex in lactating primiparous Holstein cows.
M. R. Lauber*1, B. McMullen3, J. J. Parrish2, P. M. Fricke1. 1Department of Dairy Science, University of Wisconsin-Madison Madison, WI, 2Department of Animal Science, University of Wisconsin-Madison Madison, WI, 3Bridgewater Dairy Group Montpelier, OH.

Our hypothesis was that delaying timing of AI using sexed semen relative to induction of ovulation after a Double-Ovsynch (DO) protocol for first timed artificial insemination (TAI) in lactating Holstein cows would increase pregnancies per AI (P/AI). Primiparous lactating Holstein cows from 3 US dairy farms were randomly assigned to receive a standard DO protocol with the second GnRH treatment (G2) of the breeding Ovsynch portion of the DO protocol administered 16 h before TAI (G2—16; n = 357) or a modified DO protocol with G2 administered 24 h before TAI (G2—24; n = 341). Based on an expected ovulation time between 24 to 32 h after G2, TAI for G2—16 cows occurred approximately 8 to 16 h before ovulation, whereas TAI for G2—24 cows occurred approximately 0 to 8 h before ovulation. Within each herd, cows received TAI using sexed semen (ABS Sexcel Sexed Genetics, DeForest, WI) from sires of their choosing. Sires were randomly allocated between treatments within each herd, and AI technicians were blind to treatment at TAI. Pregnancy status was assessed using transrectal ultrasonography at 34 � 3 d and 84 � 20 d after TAI, and fetal sex was determined on 2 of the 3 farms at 69 � 3 d after TAI (n = 94 and 78 cows for G2—16 and G2—24 cows, respectively). Binary response data were analyzed by logistic regression using the GLIMMIX procedure of SAS with farm included as a random effect in the model, and fetal sex ratio was analyzed by Fisher's Exact test. Contrary to our hypothesis, G2—16 cows had more P/AI than G2—24 cows at 34 � 3 d (49% vs. 43%; P = 0.06) and 84 � 20 d (47% vs. 40%; P = 0.03) after TAI. Pregnancy loss was 5% for both treatments, and fetal sex ratio did not differ between treatments (91% and 88% females for G2—16 and G2—24 cows, respectively). In conclusion, we reject our initial hypothesis; rather, delaying timing of AI using sexed semen relative to induction of ovulation after a DO protocol decreased P/AI in primiparous lactating Holstein cows.

Keywords: sexed semen, dairy cow, timing of AI.