Ameliorating the heat stress effects on maturing bovine oocytes through gamma-oryzanol supplementation

The reproductive efficiency of dairy cows decreases significantly in hot climates. Exposure to heat stress causes damage to different stages of the reproductive cycle including a decrease in the quality of oocytes. Antioxidant supplementation has been introduced as one of the main approaches to alleviate the effects of free radical damage associated with heat stress. Gamma-oryzanol (ORY), a component of rice bran oil, is introduced as a novel antioxidant. As a supplement of culture media for maturation, the effect of ORY on the development of heat-shocked bovine cumulus-oocyte complexes was evaluated in this study. At the end of maturation in vitro using the heat-shock model, a higher proportion of metaphase II oocytes (0.78 ± 0.03 vs 0.42 ± 0.03) and lower metaphase I and germinal vesicle breakdown (0.10 ± 0.02 vs 0.38 ± 0.03) were recorded for the treated group (N = 205) in comparison with the control (N = 203) (P < 0.05). Moreover, the treatment exerted upregulation of NRF2, SOD, CAT and GPX transcripts in matured oocytes and GPX in CCs, along with a considerable increase in the cleavage (0.52 ± 0.04 vs 0.33 ± 0.03) and total blastocyst rates (0.30 ± 0.03 vs 0.14 ± 0.02) (P < 0.05). These results showed that ORY increased the mRNA expression of the transcripts associated with antioxidant enzymes and enhanced the developmental potential of heat-shocked bovine oocytes and warranted further studies to explore this antioxidant's influence on improving dairy cattle's reproductive efficiency during heat stress.