In earlier research, heat stress altered follicular chemistry and suppressed subsequent luteal progesterone concentrations, whereas fan cooling resulted in increased luteal progesterone. IGF-I in the follicular fluid of lactating Holsteins after the onset of estrus. Twenty cows were randomly sorted into two groups, with one group placed in a shaded pen with fan and sprinkler cooling while the other group was assigned to a similar pen with no supplemental cooling. Approximately 8 h after observation of estrus, the ovary with the ovulatory follicle was removed surgically via standing laparotomy. Within treatment, variation for these variables was high.
Further study is needed to elucidate the cause of reduced luteal function during heat stress.