Principles and perspectives for the conservation of goat buck spermatozoa

This paper is focused on the use of alternative protocols for goat buck sperm cryopreservation and other current approaches to study sperm cryosurvival, considering theoretical principles for the preservation of cells at freezing temperatures. Simple modifications to traditional freeze-thawing protocols may improve sperm cryosurvival; thus, cooling to −5 °C instead of +5 °C, before freezing, improves buck, ram and boar sperm cryosurvival. Premature capacitation induced by cryopreservation may be used as an additional tool to: (1) assess new cryopreservation protocols; i.e. the least aggressive one would induce the lowest proportion of premature capacitated spermatozoa; (2) to estimate the subpopulation of frozen-thawed spermatozoa that remain fertile (live cells showing Pattern F or B; Chlortetracycline Assay). Freezing and storage of spermatozoa using ultra-low freezers (−150 °C) represents a feasible alternative to the use of liquid nitrogen, at least in both short and medium term. Simple tests based on simulation of osmotic stress that occurs during freeze-thawing are promising approaches to predict sperm cryosurvival. Assessment of spermatozoa during hyperosmotic and isosmotic conditions at 23 °C has revealed that proportions of plasma membrane-intact and acrosome-intact spermatozoa are similar to those observed after cryopreservation (after freeze-thawing). Inter-male differences in sperm freezability are an ever present variable influencing sperm cryosurvival.