Influence of Cortisol and Dexamethasone on Estrous Behavior of Estradiol-Treated Ovariectomized Cows and Heifers

Two experiments were conducted with estradiol-treated ovariectomized cows and heifers to determine if cortisol and dexamethasone inhibit estrous behavior. In Experiment 1, eight ovariectomized Holstein cows were subjected to weekly hormonal treatments in a replicated 4 X 4 Latin square. Treatments consisted of 500 micrograms estradiol benzoate and either 0, 40, 80, or 160 mg cortisol. During the 48 h after hormonal injection, 2-h periods of observation were alternated with 2-h periods of no observation. During each observation period, cows were observed continuously for 14 behavioral interactions that increase in frequency at estrus. Percentage of cows exhibiting estrus, interval from injection of hormones to the onset of estrus, duration of estrus, and total numbers of each behavioral interaction were similar for all treatments. In Experiment 2, 10 ovariectomized Holstein heifers were subjected to weekly hormonal treatments in a replicated 5 X 5 Latin square. Treatments consisted of 500 micrograms estradiol benzoate and either 4 mg dexamethasone, 0, 50, 100, or 200 mg cortisol. The estradiol benzoate plus dexamethasone treatment tended to lower the percentage of cattle exhibiting estrus. Interval from injection to onset of estrus, duration of estrus, and total numbers of each behavioral interaction were similar for all treatments. These data indicate that cortisol given with estradiol did not inhibit estrus in ovariectomized cows and heifers, whereas dexamethasone tended to inhibit induced estrus.