Studies on resistance of sheep to infestation with Haemonchus contortus and Trichostrongylus spp. and on the immunological reactions of sheep exposed to infestation. VI. The influence of age and nutrition on resistance to Trichostrongylus colubriformis.

Abstract

Of 10 sheep aged 3-4 years which had been born and maintained under worm-free conditions, 7 died from an initial experimental infestation with Trichostrongylus colubriformis. This mortality was in striking contrast to the results with nine-months-old sheep which had had previous experience of infestation. It demonstrated that resistance to T. colubriformis could not be ascribed to increasing age. In a group fed on a low plane of nutrition and given 40,000 or 100,000 T. colubriformis larvae, more sheep developed infestations than did similar sheep in groups given an adequate or a high-protein diet. in lambs which had been kept worm-free since birth and then dosed with 20,000 T. colubriformis larvae, infestation developed almost equally in those fed on the poor diet and those fed on the high-protein diet. The groups fed on the low plane of nutrition successfully withstood subsequent challenge doses of up to 300,000 T. colubriformis larvae. In these experiments, previous exposure to infestation apparently exercised more influence on resistance than did diet.