RESULTS OF SHEEP EMBRYOS ACCEPTANCE OBTAINED AT DIFFERENT STAGES OF DEVELOPMENT AND CRYOPRESERVED BY DIFFERENT TECHNIQUES

Abstract

This article presents data on the performance of sheep embryo transfer depending on the stage of embryo development and the method of freezing. Embryos from donor sheep of the Charollais breed were obtained after induction of polyovulation. Synchronization of the estrous cycle stage was induced by injecting a polyurethane intravaginal sponge
impregnated with 45 mg of flugestone acetate for 7 days (day of application – day 0). Follicle-stimulating hormone (Folltropin-V) was administered at a dose of 10 ml in fractions during 4 days with 12-hour intervals. Oestrus was detected by the behavioural reactions of the
ewes towards the male and the animals in heat were inseminated with freshly obtained good
quality semen. The embryos were extracted surgically (laparotomy) on days 2 and 6 after insemination. Embryos were frozen by two protocols, standard slow freezing and ultra-fast vitrification. No statistically significant difference was found between the donor groups for both
the number of yellow bodies in the ovaries and the number of washed embryos (P >0,05). Differences in the cryoresistance of embryos at different stages of embryonic development were
established in favor of the morula/blastocyst stage. No effect of cryoconservation method on
the preservation of morphological structure of embryos was found. No significant differences
were found in the acceptance rate of embryos, which were frozen by different techniques after
their transplantation to recipients. It was shown that the acceptance rate of freshly obtained
embryos, which were obtained on days 2 and 6 after insemination was significantly higher
than of frozen embryos transferred at the same stage of development. The number of lambs,
birth weight and lamb weight at 1, 2 and 4 months of age did not differ significantly between
the groups. It was concluded that collection and cryoconservation of embryos at the morula/blastocyst stage (day 6 after insemination) was a more effective technique.