Concentrações hormonais e desenvolvimento folicular de vacas leiteiras em hipertermia sazonal e aguda

The present study evaluated the seasonal and acute heat stress on follicular development and steroid and inhibin concentrations in follicular fluid, in bovine dominant follicle. Cows were distributed into four treatments: summer (n=5), autumn (n=5), animals heat stressed during the winter (n=5) and winter (n=9). On day 7 of the estrous cycle, animals were slaughtered and parameters related to follicle development were evaluated. The follicular fluid (FF) was aspirated and stored for further hormonal analysis. During the summer, the number of viable granulosa cells was 40% lower than during the winter, and there was a 45% decrease in this parameter during the autumn (P<0.05). In the winter, estradiol concentration was 62% higher than during the autumn (P<0.05) and 42% higher than during the summer (P<0.06). There was an increase in androstenedione concentration in summer group, when compared to winter (P<0.08) and autumn (P<0.05) groups. Inhibin concentration was higher in winter groups than summer and winter heat stressed groups (P<0.05). Seasonal and acute heat stress altered developmental parameters in dominant follicle and hormonal concentration in follicular fluid, those effects can partially explain the decrease in conception rates during summer.