The effects on merino lambs of chronic infection with Trichostrongylus rugatus.

Four groups of six 5-month-old merino lambs were exposed to infection with 12,000 larvae of Trichostrongylus rugatus per week and one group was killed at each of 3, 6, 9 and 12 weeks. Numbers of adult worms increased in an approximately linear manner throughout the experiment; the percentage of larvae developing to adults remained between 35 and 25% throughout the course of the experiment. Sub-total villus atrophy was evident in the anterior small intestine of each group of infected sheep and significant reductions occurred in the plasma concentrations of albumin and phosphate. Serum globulin and calcium concentrations rose in infected animals. No clinical signs were observed in infected sheep, no alteration in bone histology was detected and no decrease in growth rate occurred.