In vitro supplementation of testosterone or prolactin affects spermatozoa freezability in small ruminants.

In small ruminants, testosterone and prolactin plasma concentrations show circannual fluctuations as an adaptation mechanism to their seasonal breeding behavior. Sperm resistance to the freezing-thawing process shows seasonal fluctuation throughout the year, with lower sperm freezability at the beginning of the breeding season when prolactin and testosterone levels reach their maximum concentration. Nevertheless, whether these hormones directly affect post-thaw sperm quality parameters is still unclear. The objective was to study the effect of testosterone or prolactin added in vitro on sperm freezability in domestic ram (Ovis aries) and buck (Capra hircus). Sperm samples were incubated for 1 h with a range of testosterone (0, 2, 4, or 6 ng/mL; Exp. 1) or prolactin (0, 20, 100, 200, or 400 ng/mL; Exp. 2) concentrations. Samples were cryopreserved by slow freezing in straws at 0 h and after 1 h incubation. Sperm viability, acrosome integrity, motility, and kinetic parameters were assessed at 0 and 1 h in fresh and frozen-thawed samples. Results showed no hormone effect in fresh sperm, whereas these hormones affected post-thaw sperm parameters. In Exp. 1, in vitro incubation with testosterone decreased the post-thaw acrosome integrity of ram sperm (from 68.1 ± 6.3% to 49.6 ± 3.9%; P < 0.05). In Exp. 2, in vitro incubation with prolactin decreased the post-thaw acrosome integrity of ram (from 78.2 ± 3.4% to 66.3 ± 3.5%; P < 0.05) and buck sperm (from 81.7 ± 2.5% to 67.6 ± 3.5%; P < 0.05). Moreover, prolactin increased the post-thaw amplitude of lateral head displacement in ram sperm (from 3.3 ± 0.1 µm to 3.8 ± 0.2 µm; P < 0.05). In conclusion, either testosterone or prolactin added in vitro decreased the post-thaw acrosome integrity of ram and buck sperm. This suggests a destabilization process that could be decreasing sperm freezability when physiological levels of these hormones are high in vivo.

Effectiveness of ultra-rapid cryopreservation of sperm from endangered species, examined by morphometric means.

This study compares the effectiveness of the ultra-rapid and conventional freezing of sperm from captive bovids, giraffids, cervids, ursids, a cercopithecid, a delphinid and a phascolarctid. The relationship between sperm head dimensions and cryosurvival was also examined. Compared to conventional freezing, the ultra-rapid freezing of epididymal sperm from the dama gazelle, giraffe and brown bear returned higher cryoresistance ratios (CR, the ratio, in percentage, between the value of the variable after thawing/value before thawing) for sperm viability and motility. In the remaining species, the conventional freezing of epididymal sperm returned better CR values. The conventional freezing method also returned better CR values for ejaculated samples from all species. The head dimensions of both fresh epididymal and ejaculated sperm differed widely among species: for epididymal sperm, dolphin sperm heads were the smallest (7.189 ±â€¯0.049 µm2) and dama gazelle sperm heads the largest (43.746 ±â€¯0.291 µm2), while for ejaculated sperm, giant panda sperm heads were the smallest (15.926 ±â€¯0.150 µm2) and mouflon sperm heads the largest (38.258 ±â€¯0.104 µm2). However, no significant correlations were detected between the CR for motility, viability, membrane functional integrity or acrosome integrity and the sperm head area, either for epididymal or ejaculated sperm. In conclusion, ultra-rapid freezing is especially recommended for the cryopreservation of dama gazelle, giraffe and brown bear epididymal sperm. Sperm head dimensions appear not to be useful predictors of how well sperm might survive freezing.