Among the adverse effects of heat stress on reproductive performance, its detrimental impacts on oocyte maturation and early embryo development have been highlighted (Camargo, Costa, et al., 2019;Pavani et al., 2016). The mechanisms by which augmented temperatures compromise oocyte and embryo development are not yet well established; however, changes in the abundance of maternal transcripts that are involved in important biological functions, including various transcripts associated with mitochondrial function, have been identified as being caused by heat stress and seem to be associated with a reduction in oocyte competence and further em-

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Lentivirus vectors fail to deliver transgenes into bovine zygotes after co-incubation with sperm during in vitro fertilization [Lentivírus falham na entrega de transgenes em zigotos bovinos após coincubação com espermatozoide, durante fertilização in vitro]

The objective of this study was to evaluate the effects of dietary chromium supplementation on hepatic gene expression of lactating Girolando (Holstein x Gyr) cows under heat stress conditions in climatic chamber. Thirty-six ¾ Holstein x Gyr lactating cows were used, based on a 2x3 factorial scheme, to evaluate the effects of two diets (0 vs 0.50 mg of organic chromium kg-1 dry matter) and three environmental conditions (ECs): heat stress conditions in climatic chamber with ad libitum feeding (HS), a thermoneutral environment with ad libitum feeding (TN), and a pair-fed group in a thermoneutral environment (PF). Under HS group, the expression levels of glucose transporter 2 (GLUT2), glucose-6-phosphatase (G6Pase), and growth hormone receptor (rGH) were downregulated (P < 0.05) in chromium-supplemented cows compared to those in cows fed the control diet. GLUT2 expression was upregulated (P = 0.02) in the HS group and insulin-like growth factor 1 (IGF1) was downregulated (P < 0.01) in the PF group in cows fed the control diet compared to the expression in the TN group. No differences were observed between the ECs in terms of relative abundances of GLUT2, phosphoenolpyruvate carboxykinase (PEPCK), G6Pase, rGH, and IGF1 transcripts among the chromium-supplemented cows (P > 0.05). Heat stress caused changes in the expression of genes related to glucose metabolism, and organic chromium could modulate glucose metabolism in animals under heat stress conditions to some extent.