Fertility of high-producing multiparous lactating dairy cows inseminated with fresh or frozen sex-sorted Y-chromosome bearing semen from Angus bulls.

The objective of the present study was to evaluate the effect of artificial insemination (AI) with fresh or frozen sex-sorted semen on pregnancies per AI (P/AI) in high producing dairy cows. Multiparous cows were submitted to a Presynch-Ovsynch protocol to receive their first postpartum AI or to an Ovsynch protocol to receive their second and greater service. On the day of AI, cows were randomly assigned to 1 of 3 treatment groups: 1) receive AI with frozen conventional semen (CONV), 2) receive AI with frozen sex-sorted Y-chromosome bearing semen (SS-Frozen), or 3) receive AI with fresh sex-sorted Y-chromosome bearing semen (SS-Fresh). Semen from Angus bulls was used. Conventional semen was used at a concentration of 25 × 106 sperm cells per straw, while both sex-sorted treatments were prepared at 4 × 106 sperm cells per straw. At 32 d after AI, P/AI did not differ between cows receiving AI with CONV and SS-Fresh but was less for cows receiving AI with SS-Frozen (41.2 % vs 39.7 % vs 32.6 %, respectively). Calving per AI followed a similar pattern of the P/AI at 32 d. The proportion of male calves at calving was greater for cows inseminated with sex-sorted semen (91.4 % and 92.3 % for SS-Fresh and SS-Frozen, respectively) compared to cows inseminated with CONV semen (57.4 %). In conclusion, insemination with fresh sex-sorted semen resulted in P/AI comparable to conventional frozen-thawed semen, while insemination with frozen sex-sorted semen resulted in reduced fertility. As expected, the use of sex-sorted Y-chromosome-bearing semen increased the proportion of male beef-on-dairy calves born.