EFFECT OF HEAT-STRESS ON BOVINE EMBRYO DEVELOPMENT INVITRO

Chronic elevation of uterine temperature has long been known to increase embryo mortality in dairy cattle. Short-term elevation in temperature of mouse embryos to 43-degrees-C (acute) has been shown to induce intracellular production of heat-shock proteins. In this study, in vitro development of bovine embryos was assessed during short-term (60 h) coculture with oviduct epithelial cells at 38.6-degrees-C (T1), 40-degrees-C (T2), 38.6-degrees-C after a prior pulse treatment (20 min) at 43-degrees-C with 5% CO2 (T3), or 38.6-degrees-C after a prior pulse treatment (20 min) at 43-degrees-C with 100% CO2 (T4). During incubation, embryos cocultured at 40-degrees-C had a greater (P < .05) mean embryo development score at 36 h than embryos cocultured at 38.6-degrees-C. At 60 h of incubation, embryo development scores were greater (P < .05) for embryos cultured at 38.6-degrees-C than for those cocultured at 40-degrees-C. The number of embryos hatched at 60 h was similar after coculture at 38.6-degrees-C (T1) or a prior pulse treatment with 5% CO2 and 43-degrees-C (T3), but the embryo development score at 60 h was greater (P < .05) for the pulse-treated embryos. Embyros in T4 had greater (P < .05) embryo development scores than did T1 embryos from 36 through 60 h. Pulse treatment (T4) resulted in a greater (P < .05) number of hatched embryos at 60 h than T1, T2, and T3. These results indicate a detrimental effect of a chronic elevation in temperature that was evident shortly after embryo hatching. However, an acute rise in temperature at the morula stage increased the rate of embryo development. This may be associated with the production of heat-shock proteins that enabled embyros to tolerate the in vitro stress of the culture environment.