¹CSIRO Livestock Industries, FD McMaster Laboratory, Armidale, New South Wales, Australia

Correspondence: Dr SJ McClure, FD McMaster Laboratory, CSIRO Livestock Industries, Locked Bag 1, Armidale, New South Wales 2350, Australia. E-mail: susan.mcclure@csiro.au

Received 18 June 2008; Revised 23 September 2008; Accepted 25 September 2008; Published online 4 November 2008.

Abstract

This study investigated the hypothesis that dietary deficiency of readily available carbohydrate (raCHO) modifies the immune response of lambs to the gastrointestinal nematode Trichostrongylus colubriformis. Sixty helminthologically naive Merino lambs were fed throughout the experiment diets containing three levels of raCHO that provided adequate, moderate or low intakes according to recommended standards and were given primary or both primary and secondary infections of T. colubriformis. A further 20 uninfected lambs received the low diet for 9 weeks, after which they were returned to the standard diet. Immune status was assessed by the measurement of plasma and jejunal antibody concentrations and blood and jejunal cell numbers and function. Diets low in carbohydrate resulted in a failure of the lambs to gain weight and decreases in plasma glucose concentration, blood lymphocytes expressing CD8 or Tcr, monocytes, eosinophils, platelets and red blood cells, jejunal and plasma antibody concentrations, lymphocyte proliferation to worm antigen and numbers of jejunal CD8⁺ and Tcr⁺ lymphocytes, eosinophils and CD1b⁺ dendritic cells. Thus, a low dietary concentration of raCHOs impaired the constitutive availability of lymphocytes and antigen-presenting cells, and the cellular and humoral immunological responses. A hypothesis is suggested for the mechanism and for the possible wider implications.