The Effects of Heat Stress during In Vitro Maturation Process on The Developmental Competence of Ovine Oocytes

Background: Evidences show that farm animals such as cattle,pigs, and sheep have lower fertility in the summer than in anyother season. Recent studies demonstrate that heat stress causesinfertility not only by affecting hormonal secretion and embryodevelopment but also by damaging the oocyte. The aim of thisstudy was evaluating impacts of heat stress during the in vitromaturation (IVM) process on the developmental competence ofovine oocyte.Materials and Methods: Good quality cumulus-oocyte complexesrecovered from the aspirates of the follicles of ovineovaries were cultured in the droplets of in vitro maturation medium.The oocytes were subjected to the heat stress of ۴۱°Cduring the first ۶ (F۶-۴۱) and ۱۲ (۱۲F-۴۱) or the last ۶ (L۶-۴۱)and ۱۲ (L۱۲-۴۱) hours of IVM period. After fertilization of oocytesand cultur of resulted embryos, cleavage and blastocystformation were observed and recorded. The data were analyzedusing one-way ANOVA followed by turkey’s post-hoc test. Thedata were expressed as mean ± SEM and the differences at thelevel of P<۰.۰۵ were considered significant.Results: Results showed that duration of hyperthermic treatmentwas the determinant factor of oocytes’ response to the heatstress treatment. There was no significant difference betweenthe cleavage rates of hyperthermic treatment groups and thecontrol group although heat stressed groups had lower cleavagerate than the control group. Although the blastocyst ratesof ۶F-۴۱ and ۶L-۴۱ groups were lower than the control group,these differences were not significant. The blastocyst rates of۱۲F-۴۱ and ۱۲L-۴۱ groups (۲۳.۸ ± ۴.۹۳% and ۳۱.۸ ± ۴.۳۳%,respectively) were significantly lower than that of the controlgroup (۵۴.۶ ± ۴.۴۲%).Conclusion: This study showed that heat stress during the IVMperiod of ovine oocytes decreased the developmental competenceof oocytes and this decrease increased by increasing thetime of hyperthermic exposure.

کلیدواژه ها:

Oocyte ، Heat Stress ، Developmental Competence