Post-thaw quality of buck semen samples cooled at 5°C up to 2 days before cryopreservation

Abstract

This study aimed to assess the influence of cool storage (5 °C) prior cryopreservation over the post-thaw quality of buck semen samples. Semen of six Majorera bucks (n = 18 ejaculates) was collected, pooled and diluted in a Tris-yolk extender. Then, diluted semen was divided into six aliquots; the first aliquot (group C) was processed and frozen in liquid nitrogen (final concentration of 400 × 106 spermatozoa/mL, 12% egg-yolk and 4% glycerol). The remaining aliquots (diluted with Tris–glucose, 12% egg yolk) were hold for 1–48 h at 4 °C: R1, the semen was cooled for 1 h; R6, the semen was cooled for 6 h; R12, the semen was cooled for 12 h; R24, the semen was cooled for 24 h and R48, the semen was cooled for 48 h. After each cooling period, a second extender was added to reach a final composition (400 × 106 spermatozoa/mL, 12% egg-yolk and 4% glycerol) similar to group C; finally, semen was packed and frozen in liquid nitrogen. After freezing–thawing, the sperm motility, acrosome integrity and the percentage of abnormal spermatozoa were assessed. No differences (P > 0.05) were detected in progressive sperm motility (mean range: 35.4–39.9%) and damage acrosomes percentages (mean: 10.8–15.5%) among the control group and the cooled semen samples (R1, R6, R12, and R24) for up to 24 h; however, R48 samples showed a lower (21.6%, P < 0.01) progressive fast spermatozoa percentage and a higher percentage of damage acrosome (38.3%, P < 0.01) than those observed in the control group and in R1, R6, R12 and R24 samples. The present study confirmed that buck semen could be preserved at 5 °C for up to 24 h before freezing; however, after 2 days of chilling, semen quality experienced a notable decrease and its utility could be lower.