Although several studies have clearly shown a detrimental effect of summer heat stress on bovine reproduction, to our knowledge this has been the first time this phenomenon is related with meiotic maturation and embryonic ability to develop in vitro after stress conditions. In vivo studies have demonstrated that, up to a THI of 59, a decrease in CR occurs when AI is performed 60 to 90 days after calving. This falling in fertility was confirmed by the in vitro experiments, in which oocytes nuclear maturation and further in vitro development decreases significantly in warmer periods. Heat-shocked oocyte’s maturation also confirmed this low ability of oocytes to maturate and develop after IVF.
As THI values in hot months are lower in highest elevations, one could propose to locate animals in high elevation points during the warmest season to reduce the impact of heat stress in cow conception rate. Additional studies are needed to evaluated short time heat stress effect on both in vivo and in vitro of bovine. Moreover, developmental and growth factor genes on heat stressed oocytes and embryos can provide additional information, in the cellular level, about the factors responsible for the impairment of fertility status in hottest periods.
Although several studies have clearly shown a detrimental effect of summer heat stress on bovine reproduction, to our knowledge this has been the first time this phenomenon is related with meiotic maturation and embryonic ability to develop in vitro after stress conditions. In vivo studies have demonstrated that, up to a THI of 59, a decrease in CR occurs when AI is performed 60 to 90 days after calving. This falling in fertility was confirmed by the in vitro experiments, in which oocytes nuclear maturation and further in vitro development decreases significantly in warmer periods. Heat-shocked oocyte’s maturation also confirmed this low ability of oocytes to maturate and develop after IVF.
As THI values in hot months are lower in highest elevations, one could propose to locate animals in high elevation points during the warmest season to reduce the impact of heat stress in cow conception rate. Additional studies are needed to evaluated short time heat stress effect on both in vivo and in vitro of bovine. Moreover, developmental and growth factor genes on heat stressed oocytes and embryos can provide additional information, in the cellular level, about the factors responsible for the impairment of fertility status in hottest periods.
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