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We examined the effect of prolonged high heat stress on reproductive performance and its relationship with gene expression in pre-implantation embryos and endometrial tissue. In experiment 1, primiparous rabbit does were divided into two environments: control does (maintained between 14 and 22°C) and heat-treated does housed in a climatic chamber (maintained between 25 and 35°C). Females were reproducing, and the litter size and live born kits were assessed at 2nd and 3rd partum. In heat-treated does, lower litter size (9.7 ± 0.48 and 11.4 ± 0.50) and fewer live born kits (7.2 ± 0.55 and 10.2 ± 0.57) were observed, although similar ovulation rates and numbers of pre-implantation embryos were noted. In experiment 2, after 3rd partum multiparous non-lactating does from each experimental group were used to obtain pre-implantation embryos and endometrial tissue. mRNA transcripts from OCT-4, VEGF, erbB3, Ifn-γ, HSP70 and HSP90 were analysed by real-time qPCR. Higher values of OCT-4 expression were observed in embryos and endometrial tissue in females reproduced under heat conditions. Moreover, elevated temperatures have been shown to up-regulate VEGF in embryos and down-regulate Ifn-γ in endometrial tissue. The findings suggest a deleterious temperature effect on litter size and live born kits as a consequence of variation in gene expression pattern of the pre-implantational embryo and the endometrium associated with proliferation and differentiation and probably with implantation and uterine and foetal development during gestation.