CONSEQUENCES OF DOSE-DEPENDENT IMMUNOSUPPRESSION BY PROGESTERONE ON PARASITIC WORM BURDENS IN LAMBS

Eighteen female lambs with prior exposure to Haemonchus contortus infe ctions were ovariectomized and assigned to 1 of 3 replacement regimens : 0, 25, or 250 mg of progesterone/d delivered IM. After 3 weeks of ho rmonal treatment, all lambs were inoculated with 100,000 infective lar vae of H contortus. After 8 weeks of hormonal treatment, a blastogenic assay was performed on blood lymphocyte populations, and the abomasum from each lamb was obtained for larval and adult worm recoveries of H contortus. Lambs of the 25 mg of progesterone group had significantly (P < 0.05) reduced blastogenic response to concanavalin A and greater adult and larval populations, compared with controls. Lambs of the 25 0 mg of progesterone group had worm burdens and lymphocyte blastogenes is values intermediate between those of the other treatment groups.