Species variation in osmotic, cryoprotectant, and cooling rate tolerance in poultry, eagle, and Peregrine Falcon spermatozoa

Potential factors influencing spermatozoa survival to cryopreservation and thawing were analyzed across a range of the following avian species: domestic chicken (Gallus domesticus), domestic turkey (Meleagris gallopavo), golden eagle (Aquila chrysaetos), Bonelli’s eagle (Hieraaetus fasciatus), imperial eagle (Aquila adalberti), and peregrine falcon (Falco peregrinus). Studies focused on spermatozoa tolerance to the following: 1) osmotic stress, 2) different extracellular concentrations of the cryoprotectant dimethylacetamide (DMA), 3) equilibration times of 1 versus 4 h, 4) equilibration temperature of 4 versus 21°C, and 5) rapid versus slow cooling before cryopreservation and standard thawing. Sperm viability was assessed with the live/dead stain (SYBR-14/propidium iodine). Sperm viability at osmolalities ≥800 mOsm was higher (P < 0.05) in raptor than poultry semen. Return to isotonicity after exposure to hypertonicity (3000 mOsm) decreased (P < 0.05) number of viable spermatozoa in chicken, turkey, and golden and Bonelli’s eagle spermatozoa but not in imperial eagle or peregrine falcon spermatozoa. Differences were found in spermatozoa resistance to hypotonic conditions, with eagle species demonstrating the most tolerance. Semen, equilibrated for 1 h (4°C) in diluent containing DMA (≥2.06 M), experienced decreased (P < 0.05) spermatozoa survival in all species, except the golden eagle and peregrine falcon. Number of surviving spermatozoa diminished progressively with increasing DMA concentrations in all species. Increased equilibration temperature (from 4 to 21°C) markedly reduced (P < 0.05) spermatozoa survival in all species except the Bonelli’s eagle and turkey. Rapid cooling was detrimental (P < 0.05) to spermatozoa from all species except the imperial eagle and the chicken. These results demonstrate that avian spermatozoa differ remarkably in response to osmotic changes, DMA concentrations, equilibration time, temperature, and survival after fast or slow freezing. These differences emphasize the need for species-specific studies in the development and enhancement of assisted breeding for poultry and endangered species.