Abstract
The functioning of the stimulatory estrogen feedback mechanism during lactational anestrus of the sow was evaluated by determining the LH response to a single i.m. injection of estradiol benzoate [EB]. Estradiol-17.beta. and progesterone [P] levels were also measured following treatment and following weaning. On day 5 of lactation there was no LH response to EB, but on day 35 of lactation a small but significant (P .ltoreq. 0.05) increase in plasma LH occurred, and this was followed by a rise in plasma P in 4 of 9 animals 8 or 13 days later. Blockade of the stimulatory estrogen feedback mechanism is 1 cause of lactational anestrus in the sow.