Successful transfer of in vitro produced frozen bovine embryos with the direct transfer technique under farm conditions Short communication

Background: From the 1970's onwards, the establishment of bovine in vitro embryo production systems have been extensively studied. The first fully in vitro produced calves were born in 1987 in Japan. The first offspring from cryopreserved and in vitro produced ovine and bovine embryos born between 1994-1996 in Hungary. However, according to the authors' knowledge this is the first study describing fully in vitro produced (ovum pick up, in vitro matured, fertilised and cultured) embryos that have been frozen - thawed and transferred with the direct method resulting in successful pregnancies under farm conditions. Objectives: To produce viable, and fully in vitro produced bovine embryos under farm conditions. Materials and methods: After the ovum-pick up procedure, the cumulusoocyte-complexes have been matured, fertilized and the zygotes cultured in vitro using a commercially available and ready-to-use bovine media suite. Cryopreservation has been performed through a commercial slow freezing protocol. After thawing, the embryos have been transferred directly into synchronized recipients. Pregnancy diagnosis were carried out by ultrasonography on day 32th and confirmed by rectal palpation on day 60th of pregnancy. Results and discussion: Out of the 62 freezable in vitro produced embryos, 20 excellent quality ones have been frozen-thawed and transferred directly into synchronized recipients and 6 pregnancies have been achieved so far. The first heifer calf was born healthy on 31st March, 2020. Until now, 6 calves have been born from this program. The present results indicate that in vitro produced bovine embryos could contribute to the advanced reproductive management in beef and dairy operations in Hungary.