91 INTERACTION OF OXYGEN TENSION AND CYSTEAMINE SUPPLEMENTATION DURING IN VITRO CULTURE OF BOVINE EMBRYOS

Abstract

Reactive oxygen species damage early mammalian embryos, so culture of bovine in vitro-produced (IVP) embryos at 5% O₂ is clearly superior to 20% O₂. The thiol compound cysteamine is an antioxidant and improves in vitro blastocyst production when added to in vitro maturation (IVM) medium. The purpose of this study was to investigate supplementation of IVP embryo culture medium with cysteamine at different oxygen tensions. Bovine ovaries from feedlot heifers were collected from a local abattoir and cumulus–oocyte complexes (COC) were aspirated from 3- to 8-mm follicles. COC were matured in maturation medium with 100μM cysteamine (Reprod. Fertil. Dev. 18, 585) for 23 h in a humidified incubator at 38.5°C in 5% CO₂ in air. COC at 23 h of maturation were co-incubated with sperm for 18 h. Cumulus cells were then removed and presumed zygotes were cultured in our chemically defined culture medium system (Reprod. Fertil. Dev. 18, 585) in a 2 × 2 factorial arrangement: with or without 50 μM cysteamine × atmospheres of either 5% O₂, 5% CO₂, 90% N₂, or 5% CO₂ in air. There were no treatment differences (P > 0.01) in percentages of oocytes cleaving or reaching the 8-cell stage (Table 1). However, blastocyst production rates were lower (P < 0.01) in the group cultured without cysteamine at 20% O₂ compared with all the other groups. Adding cysteamine for embryo culture at 20% O₂ resulted in blastocyst rates similar to those cultured at 5% O₂ with or without cysteamine. Cysteamine was not beneficial at 5% O₂.

Table 1.  Cysteamine supplementation during in vitro culture of bovine embryos