38 APPLICATION OF A FIVE-DAY PROGESTERONE-BASED SYNCHRONIZATION PROTOCOL FOR TIMED AI WITH SEXED SEMEN IN DAIRY HEIFERS

Abstract

It is expected that pregnancy per AI with sexed semen would be 70 to 75% of that with conventional semen, and the use of sexed semen with timed AI (TAI) protocols is discouraged (DeJarnette et al. 2009 Theriogenology 71, 49-58). It was hypothesized that the 5-day Co-Synch + CIDR (controlled internal drug-release) protocol with 1 injection of PGF_2α would be an acceptable reproductive management program for TAI of dairy heifers with sexed semen. The objectives were to compare pregnancy per TAI (P/TAI) using conventional or sexed semen for the first TAI (experiment 1), and to evaluate P/TAI of a reproductive management program with sexed semen for the first TAI and sexed or conventional semen for the second TAI (experiment 2). A total of 1,000 Holstein heifers between 13 to 14 months of age were synchronized with the 5-day Co-Synch + CIDR protocol, that consisted of an administration of GnRH (100 μg i.m. Cystorelin^®, Merial Ltd., Iselin, NJ, USA) and a CIDR insert containing 1.38 g of progesterone inserted at Day 0; on Day 5 the CIDR was removed and one injection of PGF_2α (25 mg, i.m. Lutalyse^®, Pfizer Animal Health, New York, NY, USA) administered; on Day 8 a second injection of GnRH was administered concurrent with TAI. In experiment 1, 198 heifers were assigned randomly to be TAI with conventional (n = 98) or sexed (n = 100) semen for the first TAI. Commercial straws with sexed or conventional semen were obtained from 2 sires. In experiment 2, a total of 802 heifers received TAI to the first service with sexed semen. For the resynchronized TAI, nonpregnant heifers at 32 days after the first TAI were resynchronized with the 5-day Co-Synch + CIDR and were TAI with either sexed semen (n = 114) or with conventional semen (n = 373). Pregnancy per TAI to first and second TAI was analyzed by logistic regression using the GLIMMIX procedure of SAS (SAS Version 9.1 for Windows, SAS Institute, Cary, NC, USA) with heifer treated as a random effect. In experiment 1, P/TAI was 51.0% and 42.0% at 45 days for conventional and sexed semen, respectively (P = 0.1). Pregnancy per TAI with sexed semen was 82.3% of conventional semen. In experiment 2, P/TAI at first service with sexed semen was 35.9% at 45 days after TAI. For the second TAI, P/TAI was 40.4% with sexed semen at 45 days and 59.2% with conventional semen at 60 days (P < 0.001). As expected, P/TAI was lower with sexed compared to conventional semen. Nevertheless, the application of the 5-day Co-Synch + CIDR protocol with one injection of PGF2α, as a reproductive management program for TAI of dairy heifers, achieved an acceptable P/TAI with sexed semen. We conclude that sexed semen can be used with TAI to effectively manage reproduction in dairy heifers by removing the challenges of detection of estrus and increase the number of females born.