Collection, vitrification and post-warming transfer of equine embryos produced in vivo: a literature review

Small equine embryos, equal or smaller than three hundred micrometers in diameter (<= 300 mu m circle divide) are collected before the seventh post ovulation (PO) day. Big embryos, larger than three hundred micrometers (>300 mu m circle divide) are recovered during or after the seventh PO day. No experiments test the type of holding and washing solutions and to what extent they influence the embryo post vitrification survival. Further knowledge is needed about the mixture of cryoprotectants; either penetrating or non penetrating and the effect they exert over the embryos post vitrification survival and pregnancy rate (PVSPR). The type of embryo carrier, the size of the embryo and the volume of the vitrification solution vary between small and large embryos. A high temperature transfer index (TTI) optimizes the embryo PVSPR. In equids, the type of holding and transfer solutions used during the post vitrification step is an area scarcely explored. This study endeavors to provide information to help in the adaptation of vitrification protocols depending on the embryo size. An additional objective is to ease the access to data about the solutions employed before and during the vitrification; as well as the solutions used during the embryo warming and transfer steps.