Epididymal and ejaculated cat spermatozoa are resistant to cold shock but egg yolk promotes sperm longevity during cold storage at 4 °C

The aims were to evaluate the susceptibility of feline ejaculated and epididymal spermatozoa to cold shock and to evaluate the effect of egg yolk in the preservation extender. Ejaculated and epididymal spermatozoa from eight males were subjected to a slow (0.5 °C/min) or a fast (3 °C/min) cooling rate with controls kept in room temperature. Ejaculated and epididymal spermatozoa from another eight males were cooled in a plain Tris buffer (Tris) or in Tris with 20% egg yolk (EYT) and evaluated for 96 h. Subjective motility (MOT), plasma membrane integrity (PMI), and acrosome integrity (ACRI) were evaluated. Cooling did not induce sperm damage regarding PMI (P = 0.6) or ACRI (P = 0.19) and chilled spermatozoa had better overall MOT (P = 0.046) than controls. EYT was better for MOT (P > 0.05) from 48 h of cold storage than Tris. EYT was also better for overall ACRI (P < 0.0001) while Tris was better for overall PMI (P = 0.0004). There were no interactions between time and treatment (P > 0.05) for PMI or ACRI. Ejaculated spermatozoa had better overall MOT (P < 0.05) and PMI (P < 0.05) than epididymal spermatozoa, and higher ACRI in experiment 1 (P = 0.0003) but not in experiment 2 (P = 0.117). Source of spermatozoa did not affect the susceptibility to cooling or the effect of egg yolk as there were no interactions (P > 0.05) between source of spermatozoa and treatment (cooling or control) or between time, source and extender (P > 0.05). In conclusion cat spermatozoa were tolerant to cold shock and egg yolk was beneficial for preservation of MOT and ACRI but not PMI.