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: domest ic chicken (Gallus domesticus), domestic turkey (Meleagris gallopavo), gold en eagle (Aquila chrysaetos), Bonelli's eagle (Hieraaetus fasciatus), imper ial eagle (Aquila adalberti, and peregrine falcon (Falco peregrinus). Studi es focused on spermatozoa tolerance to the following: 1) osmotic stress, 2) different extracellular concentrations of the cryoprotectant dimethylaceta mide (DMA), 3) equilibration times of 1 versus 4 h, 4) equilibration temper ature of 4 versus 21 degrees C, and 5) rapid versus slow cooling before cry opreservation and standard thawing. Sperm viability was assessed with the l ive/dead stain (SYBR-14/propidium iodine). Sperm viability at osmolalities greater than or equal to 800 mOsm was higher (P < 0.05) in raptor than poul try 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 peregr ine falcon spermatozoa. Differences were found in spermatozoa resistance to hypotonic conditions, with eagle species demonstrating the most tolerance. Semen, equilibrated for 1 h (4 degrees C) in diluent containing DMA (great er than or equal to 2.06 M), experienced decreased (P < 0.05) spermatozoa s urvival in all species, except the golden eagle and peregrine falcon. Numbe r of surviving spermatozoa diminished progressively with increasing DMA con centrations in all species. Increased equilibration temperature (from 4 to 21 degrees C) markedly reduced (P ( 0.05) spermatozoa survival in all speci es 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 c hicken. These results demonstrate that avian spermatozoa differ remarkably in response to osmotic changes, DMA concentrations, equilibration time, tem perature, and survival after fast or slow freezing. These differences empha size the need for species-specific studies in the development and enhanceme nt of assisted breeding for poultry and endangered species.