A simple medium enables bovine embryos to be held for seven days at 4°C

Abstract

Cryopreservation methods using liquid nitrogen (LN(2)) for gametes and embryos are prevalent in mammalian artificial reproduction. However, the pregnancy rate from frozen embryos has not improved over the past two decades because freeze-thawing causes significant damage. The strict regulation of transportation of LN(2) containers by airlines also limits exchange between breeders. In this article, we introduce a medium that enabled bovine embryos to be held for up to 7 days at 4°C. A pregnancy rate of 75% (24/32) was obtained for embryos held for 7 days in this medium and transferred to primed recipients. Its constituents were medium 199, foetal bovine serum, and HEPES for buffering. This technique will enable LN(2)-free storage and air transportation of embryos provided transplantation to recipients can be completed within 7 days.

Figure 1

(a) Bovine blastocyst just after collection from the uterus. (b) Chilled embryo stored for 168 h in medium 199 with 25 mM HEPES and 50% FBS.

Figure 2. A one-day-old calf produced from a chilled embryo stored for 168 h.

Figure 3. Volume of each component in the loading procedure.