Effects of Exogenous Reproductive Hormones on Haemonchus contortus Populations in Lambs*

The potential roles of 2 reproductive hormones, prolactin and prostaglandin, in the regulation of nematode growth, fecundity, and survival in lambs were examined in 2 experiments. In the first experiment, prolactin (25 ILJ/lamb) was administered to 3 groups of lambs at 1-wk intervals during each of the first 3 wk of patency of Haemonchus contortus infections, respectively. Fecundity (eggs/female/day) and total daily egg production were significantly higher in the group treated with prolactin during week 2 of patency. Male worms were significantly longer, and female worms were significantly shorter after each weekly treatment with prolactin. In experiment 2, a prostaglandin F2a analogue, BOVILENE® (0.25 mg/lamb), was injected daily with or without exogenous prolactin (25 lU/lamb) throughout the first 3 wk of patency, the period of highest egg production. BOVILENE treatment resulted in decreased survival of both adult male and female worms and increased fecal egg concentrations, as estimated on a daily basis throughout this period. The interactions of BOVILENE with prolactin were negative relative to total daily egg production and worm growth at the terminus of the experiment (day 42 postinoculation). Additive or synergistic effects of prolactin and BOVILENE were not evident relative to fecundity. Decreased survival of worms from treatment with this potent prostaglandin analogue alone is intriguing for parasite control applications.