The influence of relative resistance and urea-supplementation on deliberate infection with Teladorsagia circumcincta during winter

The consequences for lambs of infection over the winter with Teladorsagia c ircumcincta were quantified by deliberate, trickle infection of selected an imals at 7 months of age. Infected and control uninfected animals were each allocated into four groups, relatively resistant animals on a normal diet, relatively resistant animals on an isocaloric diet supplemented with urea, and relatively susceptible animals on the same two diets. Resistance and s usceptibility was assessed by faecal egg counts following natural infection during the summer preceding the deliberate infection. During the deliberat e infection egg counts remained low and most parasites recovered at necrops y were inhibited larvae. Nonetheless, infection reduced weight gain, decrea sed albumin and fructosamine concentrations and provoked a noticeable pepsi nogen and eosinophil response. As most larvae were inhibited these response s may have been largely a consequence of immune-inflammatory responses in t he host rather than the direct action of parasites themselves. Relatively r esistant animals on the supplemented diet allowed fewer larvae to establish and had higher fructosamine concentrations, higher albumin concentrations and decreased pepsinogen responses. Therefore, a combination of relatively resistant sheep and nutritional supplementation appears most efficient at c ontrolling infection. (C) 2000 Elsevier Science B.V. All rights reserved.