Repeated acute stress during the follicular phase and luteinizing hormone surge of dairy heifers.

Seven Holstein heifers were subjected to 15-min periods of stress two times per day for 3.5 days during the follicular phase of the estrous cycle. In two of seven trials, stressed animals had no preovulatory surge in luteinizing hormone whereas in control experiments all seven had surges. Peak luteinizing hormone concentrations in the five animals having surges, as well as basal luteinizing hormone concentrations in all seven animals, were unaffected by treatment. Estrous behavior also was unaffected by stress, and all animals displayed estrus during treatment. The 24-h pattern of corticosteroids of plasma was unaffected by treatment; however, there was a significant brief elevation in corticosteroids following stress. These results suggest that brief stress can disrupt the preovulatory luteinizing hormone surge in the cow and that this effect may have significant implications for dairy management.