The effects of stress and of ACTH administration in hormone profiles, oestrus and ovulation in pigs.

Hormone concentrations and oestrous cycle patterns were studied in five chronically cannulated gilts. During oestrous cycles that were unaffected by stress, plasma oestrogen concentrations remained at basal luteal phase levels (10 to 30 pg/ml) until plasma progesterone had decreased to less than 2 ng/ml. The pre-oestrus surge of oestrogen ranged from 40 to 80 pg/ml. Plasma corticoid concentrations varied randomly and were not related to oestrogen, progesterone concentrations, or the stage of the oestrous cycle. There was, however, evidence of a positive relationship between elevated corticoid levels and observed stressful events. The stress of surgery or illness acting during the follicular phase of the oestrous cycle delayed the onset of oestrus, and corticoid levels were frequently elevated on these occasions. Elevated plasma corticoid concentrations in response to ACTH treatment were associated with either a change in the timing of or a suppression of the pre-oestrus LH peak. Altering the timing of the LH peak resulted in the formation of large partially luteinized ovarian cysts, while suppressing LH interfered with follicular development and led to small ovarian cysts. These experiments suggest that stress acting via the adrenal gland may play a role in the aetiology of infertility in sows.