Characteristics of stallion epididymal spermatozoa at collection and effect of two refrigeration protocols on the quality of the frozen/thawed sperm cells

Cryopreservation of epididymal spermatozoa is a useful tool to preserve genetic material of valuable stallions after emergency castration or unexpected death. For that, testicles and epididymides are generally sent refrigerated to the laboratory. Collection of epididymal spermatozoa is a simple procedure that reduces the volume of the material to be shipped, and may improve the quality of the chilled epididymal sperm cells. In the present study we compared the characteristics of frozen/thawed epididymal spermatozoa after refrigeration of the epididymis or after direct refrigeration of the extended epididymal sperm cells. Ejaculated sperm samples were obtained from 10 healthy stallions with at least 15 days of sexual rest, before routine orchiectomies. Spermatozoa were recovered from the epididymal tail immediately after castration (EPI), after refrigeration of the epididymis for 24 h at 4 °C (EPI R) and recovered from epididymal tail immediately after castration and stored for 24 h at 4 °C (EPI RR). Total motility, straight-line velocity, percentage of rapid cells, viability and morphological defects were similar (p > 0.05) among different treatments, and post-thaw viability was higher (p < 0.05) in EPI than in the ejaculated sperm. The similarity of post-thaw parameters led us to conclude that immediate collection and refrigeration of the epididymal sperm cells or refrigeration of the whole epididymis are equally efficient as a means of transporting material for 24 h before cryopreservation of epididymal spermatozoa.