Effects of increased ambient temperature on the development of in vitro derived bovine zygotes

Abstract

In this study, presumptive bovine zygotes were subjected to two consecutive 24-h cycles of heat treatment during the first 48 h (Experiment I) of in vitro culture (IVC) or 24 h of heat treatment during the fourth day of IVC (Experiment II). In Experiment I, the percentage of heat treatment zygotes that developed to ≥8-cell stage embryos after 72 h IVC was 2.0% ( n=459) compared with 28.4% ( n=458) for the control zygotes ( P<0.001). The subsequent yield of morulae or blastocysts after 144 h IVC for the heat treatment and control groups was 0.9% ( n=457) and 12.3% ( n=456) ( P<0.001), respectively. These results demonstrate that heat treatment during the first 48 h of IVC significantly impaired embryo development. In Experiment II, the percentage of zygotes that developed into morulae and blastocysts following heat treatment during the fourth day of IVC was 4.5% ( n=468) compared to 10.5% ( n=456) for the control group ( P<0.001). This study has demonstrated that in vitro heat stress during the critical stage of early embryo development significantly increases the incidence of early embryonic mortality.