Effect of Heat Stress on Follicular Development during the Estrous Cycle in Lactating Dairy Cattle1

TLDR

The study examined follicular development and dominance patterns under heat stress in lactating dairy cattle. Cows were assigned to cooled or heat‑stressed groups, estrous cycles were programmed with two follicular waves, prostaglandin and progesterone treatments were applied, and ovarian structures were monitored daily by ultrasonography with concurrent blood sampling. Heat‑stressed cows had higher maximal body temperatures (40.3 °C vs.

Abstract

In this study we examined, in two experiments, patterns of follicular development and dominance under conditions of heat stress. Estrous cycles were programmed to include two follicular waves (wave 1 and 2). On Day 1 of the estrous cycle (Day 0 = estrus), cows were assigned randomly to cooled (C; n = 6) or heat-stressed (H; n = 6) groups. In experiment 1, on Day 12 prostaglandin (PG) F2α, was injected and a controlled intravaginal drug release device (1.9 g progesterone) was inserted (this was removed on Day 17). In experiment 2, PGF2α, 0 was injected on Day 14. Ovarian structures were examined daily by ultrasonography, and blood samples were collected at each scanning. Cycle lengths were 20 and 17 days in experiments 1 and 2, respectively. Mean maximal body temperatures were higher (p < 0.01) in H (40.3°C) than in C (38.8°C) cows.