Fertility in heifers and cows after low dose insemination with sex-sorted and non-sorted sperm under field conditions.

The present study was performed to test fertility after low dose insemination with sexed and non-sexed sperm in dairy cattle under field conditions in Switzerland. Spermatozoa were stained with Hoechst 33342 and sorted by flow cytometry. A total of 132 heifers and cows were inseminated with 2 x 10(6) X-bearing, frozen-thawed sperm (A) and 91 animals were inseminated with the same dose using non-sorted, frozen-thawed sperm (B). Pregnancy examination by ultrasound was performed twice, 30-40 days (PE1) and 70-90 days (PE2) after insemination. The pregnancy rates after PE1 were 33.3% (9/27) and 59.3% (16/27) in heifers (P=0.05) and 27.6% (29/105) and 28.1% (18/64) in cows (P>0.05) for groups A and B, respectively. Embryonic losses between PE1 and PE2 in heifers were 11.1% (1/9) and 0% (0/16) and in cows 17.2% (5/29) and 5.6% (1/18), the differences between groups A and B not being significant (P>0.05). Calving rates in heifers were 29.6% (8/27) and 57.8% (15/26), whereas in cows 22.1% (23/104) and 23.4% (16/63) gave birth to calves (for both groups P>0.05). The sex ratio was different (P<0.05) between A (85.3%) and B (58.6%). From our results it can be concluded that conception rates of sorted and non-sorted semen are similar using an insemination dose of 2 x 10(6). Fertility may be increased by improving sexing technology and animal management.