Effect of diluent type, cryoprotectant concentration, storage method and freeze/thaw rates on the post-thaw quality and fertility of cryopreserved alpaca spermatozoa

Abstract

This study compared protocols for cryopreservation of ejaculated, papain-treated alpaca spermatozoa. This included different concentrations of egg yolk (EY; 5, 10 or 15%) and glycerol (2, 5 or 10%), diluent types (SHOTOR, lactose, skim milk or INRA-96™), freeze rates (2, 4 or 8 cm above liquid nitrogen; LN), thaw rates (37 °C for 1 min or 42 °C for 20 sec) and storage vessels (pellets, 0.25 mL straws or 0.5 mL straws). Spermatozoa were assessed pre-freeze and 0, 30, 60 and 90 min post-thaw. Forty-one hembras were inseminated with either fresh, papain-treated or frozen-thawed spermatozoa. Motility was affected by EY concentration (P < 0.001), diluent type (P < 0.001), freeze rate (P = 0.003) and storage vessel (P = 0.001). Viability was affected by EY concentration (P < 0.001), diluent type (P < 0.001), storage vessel (P = 0.002) and thaw rate (P = 0.03). For artificial insemination (AI), semen was diluted 1:3 in a lactose-based diluent, with 5% EY and glycerol. Freezing was in 0.5 mL straws, 2 cm above LN for 4 min then thawing at 37 °C for 1 min. Pregnancy rates of those ovulated (n = 26) were not different (1/5 fresh, 1/4 papain-treated, 0/17 frozen-thawed; P = 0.10). Pregnancy can be achieved after AI with papain-treated spermatozoa. Further work is needed to determine the optimal dose, timing and location for insemination.