In vitro supplementation of trans-10, cis-12 conjugated linoleic acid ameliorated deleterious effect of heat stress on bovine oocyte developmental competence.

Environmental stresses, such as heat stress (HS), have been shown to have diverse effects on the developmental competence of oocytes. The aim of this study was to determine the effect of exogenous conjugated linoleic acid (CLA) supplementation in maturation medium on bovine oocyte maturation and developmental competence under HS condition. Accordingly, cumulus-oocyte complexes (COCs) were cultured at 41 °C and 38.5 °C for the first and second 12 h of maturation in the presence of 0 (PC), 50 (CLA50-HS) and 100 (CLA100-HS) μM CLA. Also, a group of COCs were cultured at 38.5 °C for 24 h of maturation without CLA supplementation as negative control (NC). Nuclear maturation, level of intracellular glutathione (GSH), reactive oxygen species (ROS) content, cleavage and blastocyst rates as well as relative expression of BAX, and BCL2 genes in blastocysts were investigated. Our finding for the PC and NC groups revealed that HS decreased the percentage of MII oocytes, cleavage and blastocyst rates (P < 0.05). Moreover, HS lead to an increase in ROS levels and relative expression of BAX gene, decreased the intracellular content of GSH and relative expression of BCL2 gene (P < 0.05). However, the cleavage and blastocyst rates tended to increase in the CLA-supplemented groups compared to PC group (p < 0.10). Also, ROS and GSH levels in the matured oocytes decreased and increased in the CLA50-HS group compared to the PC group (P < 0.05), respectively. The ratio of expression levels of BAX to BCL2 genes was not different between the PC and CLA50-HS groups (P > 0.05). These findings suggest that HS has undesirable effects on the maturation competence of bovine oocyte and subsequent embryo development while administration of CLA can ameliorate some of adverse effects of HS.