All 8 embryos were dt-vitrified in the Minitube EquiPRO + BSA-V system. A total of 9 mares were flushed on Day 6.5, and 8 excellent to good morulae were recovered. Minitube EquiPRO + BSA-V was used with in vivo-produced equine morulae (no capsule). Of 90 IVP cattle embryos cryopreserved with Minitube EquiPRO + BSA-V, 40 (44.4%) embryos were viable after 24 h of culture. Of 121 IVP cattle embryos cryopreserved with Minitube EquiPRO + 10% FBS, 52 (42.9%) embryos were viable after 24 h of culture. Of 103 IVP cattle embryos cryopreserved by the CSU method, 45 (43.7%) embryos were viable after 24 h of culture. Minitube BSA-V is highly defined and internationally compliant BSA approved for use in raw form or in culture medium in the United States and European Union. Two different Minitube EquiPRO-based dt-media with either 10% FBS or Minitube BSA-V (Fraction-V Minitube of America Inc.) were tested on IVP cattle embryos. Equine Pract 22, 831–841) was used on IVP cattle blastocysts. As a control, the Colorado State University equine embryo dt-vitrification system (CSU Carnevale EM Vet. Only excellent to good morula-blastocyst stage IVP cattle embryos were used in this study. Prospective embryos were cultured for 120 h in CR-1/BSA (Minitube of America Inc.), and then supplemented with 10% fetal bovine serum (FBS) and cultured for an additional 48 h. After 22 h of IVM, mature COC were placed into standard IVF. Only COC surrounded by 2 or more layers of compact cumulus investment and containing oocytes of equal size were placed into a commercial TCM-199-based IVM system (Minitube of America Inc., Verona, WI). Cumulus–oocyte complexes (COC) were aspirated from 2- to 6-mm follicles with an 18-gauge needle fixed to a vacuum pump system. Ovaries were collected from mature females at an abattoir and transported to our laboratory.

We explore the use of standard in vitro-produced (IVP) cattle embryos for the development of a direct transfer (dt) equine embryo cryopreservation system. Unfortunately, there is no reliable in vitro system available to provide a routine and economical source of equine embryos for research and commercial use.

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