Semen Quality of the First and Second Ejaculates Collected from Breeding Inactive Stallions after Cooling and Freezing

Abstract

This study aimed to assess the semen quality after the cooling and freezing of the first and second ejaculates of the season, which were collected 1 h apart. After collection (n = 40 ejaculates), the gel-free semen volume, concentration, total number of sperm, and sperm morphology were determined. An aliquot of each ejaculate was extended and cooled for 48 h; a second aliquot was cushion-centrifuged and cooled for 48 h; and a third aliquot was processed and then frozen. The total motility (TM) and progressive motility (PM), plasma membrane integrity (PMI), and high mitochondrial membrane potential (HMMP) were assessed pre-(0 h), 24 h, and 48 h post-cooling and before and after freezing. The second ejaculate had a lower gel-free semen volume (p = 0.026). The sperm concentration was greater in the first than in the second ejaculate (p < 0.001). The sperm morphology was similar between the ejaculates (p > 0.05). Cushion-centrifugation prevented a reduction in the TM, PM, and PMI over time (p < 0.05). The TM, PM, and PMI decreased after freezing but not between the ejaculates (p > 0.05). The first and second ejaculates of the season, which were collected 1 h apart, varied in quantity but not in quality after cooling and freezing.