Faecal dry matter, inflammatory cells and antibodies in parasite-resistant sheep challenged with either Trichostrongylus colubriformis or teladorsagia circumcincta.

Abstract Sheep that are highly resistant to parasitic nematodes can suffer bad diarrhoea due to the inflammation associated with rejection of ingested larvae from pasture. We hypothesised that challenging parasite-resistant sheep indoors with nematode larvae would result in reduced faecal dry matter, and that faecal dry matter would be lowest in sheep challenged with a mixture of Trichostrongylus colubriformis and Teladorsagia circumcincta compared to those challenged with either species alone. We also hypothesised that inflammatory cells and serum antibodies and interluekin-5 would be highest in those sheep that received the mixed larval challenge. We found that faecal dry matter was reduced ( P Tric. colubriformis . At 14 and 23 days after challenge began, there were no differences in faecal dry matter between the three challenged groups. Within the abomasum, there were no differences in inflammatory cell numbers between unchallenged sheep and those challenged only with Tric. colubriformis . Cell numbers in sheep challenged with Tela. circumcincta were higher ( P Tela. circumcincta or as a mixed challenge. In the small intestine, inflammatory cell numbers were higher ( P Tela. circumcincta or Tric. colubriformis were also slightly higher than those in controls. Larval challenge increased ( P P Tela. circumcincta and Tric. colubriformis can cause immune-mediated diarrhoea in sheep, and that a mixed challenge will not necessarily lead to worse diarrhoea or higher concentrations of antibodies in serum. We also concluded that challenge with Tric. colubriformis leads to no inflammation in the abomasum, but challenge with Tela. circumcincta may lead to some inflammation in the small intestine.