Protein supplementation but not oral vaccination with infective larvae accelerates the development of resistance to Trichostrongylus colubriformis of grazing Merino weaners

Abstract

This experiment was designed to test the effectiveness of oral vaccination with infective larvae and protein supplementation in accelerating the development of resistance of grazing Merino weaners (6 months old) to infection with T. colubriformis. Animals grazed as a single flock and received 3 times each week either 0 or 140 g/day cottonseed meal (CSM). Within each level of supplementation animals were either repeatedly treated with anthelmintic to preclude infection, exposed to field infection or vaccinated with a total of 42,000 T. colubriformis L3 in 8 doses over an 18 day period. After 7 weeks all infections were terminated and all animals received a challenge infection with 24,000 T. colubriformis L3. Four weeks after challenge worm counts were determined. Sheep that received CSM grew faster (45 g/day) and when exposed to field infection had a FEC 67% lower than nil fed animals. Worm counts after challenge were not affected by vaccination but were 28% lower in animals previously fed CSM. In summary, supplementation with CSM hastened the development of resistance to T. colubriformis but vaccination was ineffective.