Effects of exogenous progesterone and/or prolactin on Haemonchus contortus infections in ovariectomized ewes

Reproduction can alter the course of ovine nematodiasis; fecal nematode egg concentrations often increase near lambing and throughout lactation, a phenomenon referred to as the periparturient rise. To identify the host mechanisms that might link these disparate events, i.e. lactation and the fecundity of gastrointestinal trichostrongyles, ovariectomized ewes were injected daily with progesterone and/or prolactin, or saline. Progesterone treatment commenced 20 days before inoculation with Haemonchus contortus and prolactin was administered throughout the 30-day infection period. Ovariectomized ewes receiving prolactin during the experimental infection maintained higher daily fecal egg concentrations than the progesterone, progesterone/prolactin, or the control treatment groups. However, ovariectomized ewes that received 20 days of pre-inoculation exposure to progesterone, as well as prolactin during the infection, had greater numbers of nematodes that were larger than the other treatment groups. Thus, the sequential delivery of these hormones that are associated with the reproductive cycle in ewes produced some of the same results that occur during periparturient rise.