Fertility in single-ovulating and superovulated dairy heifers after insemination with low dose sex-sorted sperm.

The present study was performed to test fertility in single-ovulating and superovulated dairy heifers after insemination with low dose sex-sorted sperm under field conditions. Some parameters, including the dosage, deposition site and timing, were assessed with the pregnancy rates after artificial insemination (AI). Moreover, the use of oestrus synchronization in combination with sorted sperm was evaluated. Besides that, we also improved the embryo production efficiency in superovulated dairy heifers by optimizing the timing of inseminations and repartitioning the sexed sperm dosage among multiple inseminations. The conception rate (52.8%) in heifers after low dose (2 × 10(6) ) insemination with sorted sperm deep into the uterine horn did not differ (p > 0.05) from that (59.6%) of conventional AI (1 × 10(7) non-sorted sperm) and that of deep insemination with low dose non-sorted sperm (57.7%). There was also no difference (p > 0.05) between conception rates after single (51.7%) and double (53.8%) deep insemination with sorted semen. Heifers inseminated with sorted sperm at synchronous oestrus had a lower pregnancy rate (48.1%) than heifers at spontaneous oestrus (53.6%), but this did not reach statistical difference (p > 0.05). The average number of transferable embryos collected in vivo from heifers inseminated with sorted sperm (4.81 ± 2.04) did not differ (p > 0.05) from that obtained from heifers after insemination with non-sorted sperm (5.36 ± 2.74). Thus, we concluded that the pregnancy rate after deep intra-uterine insemination with low dose sorted sperm was similar to that of non-sorted sperm, which was either also deposited at a low dose deep intra-uterine or into the uterine body. Synchronization of oestrus can be beneficial in combination with sorted sperm to optimize the organization and management of dairy herds. The results from superovulated heifers demonstrated that our insemination regime can be used to obtain a comparable embryo production efficiency with sorted sperm than with non-sorted sperm.