The interaction of infections of Haemonchus contortus and Nematodirus battus in lambs : I. The effect of massive infections of Haemonchus on subsequent infections of Nematodirus

Abstract

Massive infections of Haemonchus contortus produced in lambs a rise in abomasal pH 3 to 4 days after infection associated with the absence of free HCl, a fall in total acidity and a rise in Na + concentration. This rise in pH was confined to the first quarter of the small intestine. The plasma pepsinogen levels rose sharply between 1 to 4 days after infection and the haematocrits fell by day 15. The populations of Haemonchus on day 19 were composed of late fourth stage female and early fifth stage male larvae. Infections of Nematodirus battus were established in the small intestine, using both normal and artificially exsheathed infective larvae, when the omasal pH was normal and when it had been raised during Haemonchus infections. A highly acid abomasal environment did not appear to be necessary for exsheathment of the larvae of Nematodirus in vivo. Single infections of both normal and exsheathed Nematodirus reached patency 15 days after infection. In the presence of Haemonchus infections, a proportion of Nematodirus was inhibited at the fourth larval stage and the development of the remainder through the fifth stage was slowed down.