Effects of a high-energy diet on oocyte quality and in vitro embryo production in Bos indicus and Bos taurus cows

The effects of different dietary energy levels [100 and 170% for maintenance (M) and high energy (1.7M), respectively] on metabolic, endocrine, and reproductive parameters were evaluated in nonlactating Bos indicus (Gir; n = 14) and Bos taurus (Holstein; n = 14) cows submitted to ultrasound-guided ovum pick-up followed by in vitro embryo production. The oocyte donor cows were housed in a tiestall system and fed twice daily (0800 and 1600 h). Twenty-one days before the beginning of the experiment, the animals were fed with a maintenance diet for adaptation followed by the experimental diets (M and 1.7M), and each cow underwent 9 ovum pick-up procedures 14 d apart. The recovered oocytes were cultured in vitro for 7 d. We measured glucose and insulin concentrations and performed glucose tolerance tests and the relative quantification of transcripts (PRDX1, HSP70.1, GLUT1, GLUT5, IGF1R, and IGF2R) from the oocytes recovered at the end of the experimental period. No interactions were observed between the effects of genetic groups and dietary energy level on the qualitative (viable oocytes, quality grade, and oocyte quality index) and quantitative (oocytes recovered) oocyte variables. There were no effects of dietary energy level on the qualitative and quantitative oocyte variables. However, Bos indicus cows had greater numbers of recovered structures, viable oocytes, and A and B oocyte grades as well as better oocyte quality index scores and lower DNA fragmentation rates compared with Bos taurus donors. In vitro embryo production (cleavage and blastocyst rates and number of embryos) was similar between diets, but the 1.7M diet reduced in vitro embryo production in Bos indicus cows after 60 d of treatment. Moreover, Bos indicus cows on the 1.7M diet showed lower transcript abundance for the HSP70.1, GLUT1, IGF1R, and IGF2R genes. All cows fed 1.7M diets had greater glucose and insulin concentrations and greater insulin resistance according to the glucose tolerance test. In conclusion, increasing dietary energy did not interfere with oocyte numbers and quality, but the 1.7M diet reduced in vitro embryo production in Bos indicus cows after 60 d of treatment. Finally, Bos indicus cows had greater oocyte quality, greater numbers of viable oocytes and greater in vitro embryo yield than Bos taurus.