In vitro sperm characteristics and in vivo fertility of sex-sorted and conventional semen in suckled Nelore cows at a traditional schedule for timed-AI with estrus detection

The aim of this study was to assess in vitro sperm characteristics and pregnancies/AI (P/AI) of conventional and sex-sorted semen at timed-AI of suckled, multiparous Nelore cows. All cows (n=348) were submitted to a traditional estradiol/progesterone(P4)-based protocol. At 48h after P4-device removal, the estrous behavior was recorded, and AI was performed with conventional or sex-sorted semen from two bulls. The following sperm assessments were performed: CASA, Hyposmotic Test, sperm morphometry and chromatin structure by TB staining. P/AI were reduced ( P<0.001) for sex-sorted compared to conventional semen in cows expressing estrus (27vs47%) or not (11vs.37%). Membrane integrity ( Bull1: 30.3 +/- 9.6 vs. 52.3 +/- 12.4%, P=0.01; Bull2: 24.5 +/- 3.0 vs. 48.7 +/- 1.6%, P=0.006) and sperm concentration (Bull1: 23.2 +/- 0.6 vs. 43.0 +/- 0.8x106sperm/mL, P<0.001; Bull2: 25.1 +/- 2.8 vs. 42.1 +/- 0.7x10(6)sperm/mL; P<0.001) were reduced in sex-sorted compared to conventional semen, for both bulls. Total and progressive motility were reduced in sex-sorted semen for Bull1 (TM: 49.7 +/- 15.9 vs. 94.9 +/- 1.9%, P=0.007; PM: 16.7 +/- 3.4 vs. 44.1 +/- 13.2%, P=0.009) and no differences were detected for Bull2 (TM: 45.0 +/- 17.5 vs. 68.2 +/- 19.1%, P=0.098; PM: 12.8 +/- 4.7 vs. 30.0 +/- 13.0%, P=0.065). Sperm ellipticity from sex-sorted was lower than conventional semen for Bull2 (0.306 +/- 0.01 vs. 0.342 +/- 0.02, P=0.02) and no difference was detected for Bull1 (0.332 +/- 0.01 vs. 0.330 +/- 0.01, P=0.55). Reduced in vivo fertility was observed for sex-sorted semen, regardless of estrous behavior. In vitro sperm quality of sex- sorted semen was compromised for both bulls, but differently affected for each sire.