ABSTRACT
Two experiments were designed to evaluate the effect of different insemination times (12 and 24h or 18 and 30h) and different types of semen (sex-sorted or non-sorted sperm) on embryo production in Nelore (Bos indicus) and Holstein (Bos taurus) superstimulated donors. In the first experiment, hormonal superstimulation of ovarian follicular development in Nelore donors (n=71) was performed in randomly allocated animals to one of the three treatment groups, and they were inseminated at 12 and 24h after an ovulatory stimulus with pLH treatment was applied, either with sex-sorted (4.2×10(6) sperm/insemination; S12/24; n=17) or non-sorted sperm (20×10(6) sperm/insemination; NS12/24; n=18), or they were inseminated at 18 and 30h using sex-sorted sperm (4.2×10(6) sperm/insemination; S18/30; n=19). A greater number of transferable embryos were found when sex-sorted sperm was used to inseminate the animals at 18 and 30h (4.5±3.0) compared to insemination at 12 and 24h (2.4±1.8; P<0.001). However, a greater embryo production (6.8±2.6) was obtained with non-sorted sperm. In the second experiment, the same insemination times and semen types were used in lactating high-production Holstein cows (n=12). A crossover design was employed in this trial. A lesser embryo production (P=0.007) was found in Holstein donors that were inseminated using sex-sorted sperm at 12 and 24h (4.6±3.0) compared to non-sorted sperm (8.7±2.8). However, intermediate results were obtained when the inseminations with sex-sorted sperm were performed at 18 and 30h (6.4±3.1). These results supported the current hypothesis that it is possible to improve embryo production using sex-sorted sperm in B. indicus and B. taurus superstimulated donors when the inseminations are performed near the same time as time-synchronized ovulations. However, the embryo production for timed artificial insemination (TAI) with sex-sorted sperm was still less than the production with non-sorted sperm.
