Ovarian activity and oocyte quality associated with the biochemical profile of serum and follicular fluid from Girolando dairy cows postpartum

This study was designed to evaluate the influence of heat stress (HS) on the metabolic profile of serum and follicular fluid (FF), ovarian follicle development, and oocyte quality of Girolando dairy cows. Oocytes, blood, and FF (follicles ≥9 mm) samples were obtained at 30, 45, 60, 75, and 90 days postpartum in the summer and winter seasons. During transvaginal follicular aspiration, rectal temperature (RT), body condition score (BCS), number of ovarian follicles, and quality of oocytes were recorded. The ambient air temperature (AT) and relative humidity (RH) were also recorded to calculate the temperature humidity index (THI). Glucose, total cholesterol (TC), triglycerides (TG), urea, sodium (Na), potassium (K), and calcium (Ca) concentrations were determined using serum and FF samples. The RT, THI, and BCS loss were greater (P < 0.01) in the summer; however, glucose, Na, and K serum concentrations decreased in the same season (P < 0.05). Degenerated oocytes were positively associated (P < 0.05) with THI (r = 0.14) and AT (r = 0.13), and negatively associated with glucose (r = −0.12) and K (r = −0.11) serum concentrations. HS induces metabolic changes, which compromise the number of ovarian follicles and the follicular environment, thus resulting in morphologically damaged oocytes.