112 Comparative study between slow freezing and vitrification on the survival rate of cryopreserved alpaca embryos post-transfer

Abstract

The objective of this study was to compare the effectiveness of cryopreserving in vivo-produced alpaca embryos by slow freezing v. vitrification. The embryos were produced from 9 female alpacas at Fundo Mallkini, Puno, Peru, located at 4300 m elevation. The donor alpacas were synchronized by induction to ovulate with an injection of gonadotropin-releasing hormone (0.0084 mg of buserelin acetate) and natural mating with vasectomized males to male receptive donors (day of ovulation induction was considered Day 0). On Day 2, the donors were injected 700 IU of eCG. On Day 7, the donors received an injection of prostaglandin F_2α (0.25 mg of cloprostenol) and were mated on Day 8 by fertile males (2 matings 12 h apart: 0600 and 1800 h). The embryos were collected at 5.5 days after fertile mating and were graded as per IETS recommendations; most of the embryos were already expanded and hatched blastocysts. Embryos were washed and maintained in holding medium (1 L PBS + 1 g Glucose + 36 mg sodium pyruvate + 0.4% BSA + 50 mg kanamycin monosulfate) at 23°C for up to 1 h and distributed into 2 groups for either slow freezing for direct transfer (n = 14 embryos) or vitrification (n = 10 embryos). Slow freezing consisted of transfer into freezing medium (9 mL of 1.5 M ethylene glycol + 1 mL of 1.0 M sucrose prepared in holding media) at 23°C, placing in 0.25-mL straws and subjected to freezing at a rate of −0.5°C/ minute to −35°C and then plunging into LN. Vitrification followed a procedure described for camel embryos whereby embryos were exposed to solutions containing increasing amounts of glycerol and ethylene glycol for fixed periods and were then loaded into an open pull straw and plunged directly into LN for storage. The cryopreserved embryos were transferred into adult alpacas at the Community of Suitucancha, Junin, Peru (1500 km from the farm where the embryos were collected and cryopreserved, 4200 m elevation). Embryos in the slow-freezing group were thawed in warm water at 37°C for 30 s and loaded directly into the embryo transfer gun for direct transfer into 7 alpaca recipients (2 embryos per recipient). Vitrified embryos were warmed by removing the open pull straw from the LN and transferring the embryos to 2 warming solutions at 37°C with decreasing levels of vitricants and containing 0.5 M galactose with a final incubation at room temperature in holding media and then transferred into 5 alpaca recipients (2 embryos per recipient). The embryos were transferred into synchronized recipients by transcervical nonsurgical method. Pregnancy diagnosis was made by transrectal ultrasound examination at 45 days post-transfer. The pregnancy rates in the slow-freezing and vitrification groups, respectively, were 2/7 (29%) and 0/5 (0%); the difference was not significant (P > 0.05) based on Fisher’s exact test. Twin pregnancies were not detected. We consider the result with slow freezing very promising, as in previous trials we had less than 18% pregnancies. More trials with larger number of embryos per cryopreservation method are being programmed.