PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: Influence of cattle genotype (Bos indicus vs. Bos taurus) on oocyte and preimplantation embryo resistance to increased temperature1,2

Abstract

High environmental temperatures during the hot months of the year reduce reproductive performance in cattle. Summer heat stress depression in fertility is a multifactorial problem; however, there is evidence that the bovine germinal vesicle and maturing oocyte, as well as the early embryo, are major targets of the deleterious effects of heat stress. Such adverse effects are less pronounced in heat-tolerant breeds (Bos indicus) than heat-sensitive breeds (Bos taurus). This genetic variation results from the greater thermoregulatory ability and cellular thermoresistance of heat-tolerant breeds. Heat-induced oocyte cellular damage occurs in both cytoplasmic and nuclear compartments. Heat shock has been shown to reduce oocyte nuclear maturation, induce apoptosis, compromise oocyte cytoskeleton, and impair oocyte mitochondrial function and developmental competence. However, the oocyte cytoplasm is more susceptible to heat shock than the nucleus. This effect is greater for Bos taurus than Bos indicus oocytes. The detrimental effects of heat shock are also critical during the first cleavage divisions when most of the embryonic genome is inactive; however, the bovine embryo becomes more resistant to increased temperature as it proceeds through development. Several studies demonstrated that Bos indicus embryos are more thermotolerant than Bos taurus embryos. Adaptive changes involved in acquisition of thermotolerance are likely derived from changes in gene expression and (or) activity of biochemical molecules that control cellular functions against stress. Recently, molecules such as IGF-I and caspase inhibitor z-DEVD-fmk have been shown to exert a thermoprotective role, rescuing heat-induced oocyte and embryo cellular damage and developmental competence. Therefore, cattle genotype and thermoprotective molecules can be considered as an alternative to modulate the effects of increased temperature in reproductive function.

PHYSIOLOGY AND ENDOCRINOLOGY SYMPOSIUM: The current status of heat shock in early embryonic survival and reproductive efficiency1,2

“…Breed differences between Bos indicus and Bos taurus cattle contribute to heat tolerance and improved fertility under heat stress conditions (Paula-Lopes et al, 2013). Heat can induce cellular damage in both the cytoplasm and the nucleus of the oocyte.…”

Du diagnostic préimplantatoire au suivi de troupeau : que peut apporter la génomique aux éleveurs ?

“…Enfin, il a été montré que les ovocytes, les embryons, les lymphocytes, et les cellules de l'oviducte et de l'endomètre ont une plus grande tolérance à la chaleur pour les génotypes Bos indicus que pour Bos taurus (Paula Lopes et al, 2013). Cette variation génétique se traduit par une plus grande capacité de thermorégulation et de thermorésistance cellulaire dans ces races.…”

“…En général, le stress thermique restreint la compétence de développement ovocytaire car il induit des phénomènes d'apoptose, endommage le cytosquelette des ovocytes, et altère la fonction mitochondriale. Les effets délétères du stress thermique sur l'efficacité des biotechnologies de la reproduction pourraient donc être modulés par des outils de génomique personnalisés, tels une liste supplémentaire de SNP (Paula Lopes et al, 2013).…”

Effects of prolonged exposure of mouse embryos to elevated temperatures on embryonic developmental competence

“…12 to 24 h), (Barros et al, 2006;Hansen, 2009;Paul et al, 2008;Paula-Lopes et al, 2013;Sharpe, 2010). In domestic animals and mouse studies, elevated temperature affects oocyte maturation and embryonic development because oocytes/early cleaving embryos prior to zygotic gene activation are more vulnerable to heat stress, and the heat-stressed oocytes/ embryos show impaired capacity to implant and to carry a pregnancy to term (Ealy and Hansen, 1994;Edwards and Hansen, 1997;Elliott and Ulberg, 1971;Monty Jr and Racowsky, 1987;Ulberg and Burfenin, 1967).…”