Haemonchus contortus third stage larvae in sheep: kinetics of arrival into the abomasum and transformation during rumino-omasal transit.

The kinetics of passage of Haemonchus contortus third stage larvae through the omasoabomasal orifice were analysed in sheep for six hours after their administration by the nasooesophageal route. The larvae moved into the abomasum more slowly than the liquid phase of the ruminal contents. They arrived in three different forms: sheathed, exsheathed or coiled. A very small number of exsheathed larvae seemed to be necessary for inducing early modifications in permeability of the abomasal mucosa.