Age resistance of sheep to infestation with the nematodes, Nematodirus filicollis and Nematodirus spathiger

Abstract

Extract

The phenomenon of age resistance to nematode parasites has been reported to occur in a variety of animals and the literature has been reviewed by Herlich (1960). He points out that, in the case of parasites of ruminants, much of the evidence is based primarily on field observations of naturally infected animals. In such circumstances, previously acquired specific immunity cannot be ruled out as a causal factor. Furthermore, the interpretation of much of the published experimental work on age resistance to the family Trichostrongylidae is equivocal.