Experimental hyper-progesteronemia increases the egg shedding and fertility of Haemonchus contortus in sheep

Hyperprogesteronemia effects on the establishment and fertility of Haemonchus contortus were measured in an experimental infection in gonadectomized male lambs. Sixteen lambs were divided into two groups. Lambs from the progesterone (PG) group (n = 8) were implanted subcutaneously at week -2 with two devices (CIDR 330, Zoetis lab®) containing 600 mg of ovine progesterone. The second group (n = 8) was not implanted and served as the control. Lambs from both groups were inoculated intra-ruminally with 5000 L₃ of H. contortus at week 0. All lambs were humanely euthanized at week seven p.i. All lambs in the PG group exhibited hyperprogesteronemia at the time of H. contortus infection. They had higher fecal egg and blood eosinophil counts than lambs in the control group (p < 0.04). The female worms in the PG group had higher fertility (p < 0.04) than those in the control group. No differences (p > 0.05) were observed in adult worm numbers in the abomasum, female/male ratio, or antibody levels in both groups. The increase in serum progesterone levels in orchiectomized lambs at the time of infection stimulated an increase in H. contortus fertility, and consequently, in fecal egg counts. The above results show that the H. contortus parasite can recognize and respond to the presence of progesterone in vivo, strongly suggesting that this hormone plays a relevant role in the transregulation observed during peripartum rise.