The effect of continuous doses of Trichostrongylus colubriformis larvae on the intestinal mucosa of sheep and on liver vitamin A concentration.

Eight 7-month-old sheep were dosed continuously with Trichostrongylus colubriformis larvae and 4 sheep were killed at 5 and 10 weeks from the commencement of infection. Flattening of the mucosa and villous atrophy were commonly present at slaughter, and parasites were often found in superficial channels parallel with the luminal surface. At 10 weeks the mucosa was thickened and highly cellular. Leucine aminopeptidase, alkaline phosphatase and maltase activity were reduced in the proximal third of the small intestine. Liver vitamin A was reduced in 3 of 4 infected sheep at 10 weeks, but serum vitamin A levels were comparable with those of worm-free control sheep throughout the experiment.