Metabolic effects of host defence responses during gastrointestinal parasitism in sheep

Abstract

Following stimulation of the immune system, tissue trauma, or exposure to some stressors, there can be activation of the acute phase response (APR). This is a primitive defence reaction that helps protect the host against noxious insults. Part of the response involvess a change in priorities for nutrient utilisation, when the pro-inflammatory cytokines IL-1α/β, TNFα, IL-6 and IFNα/β override the normal hypothalamic-somatotropic control of nutrient utilisation. The pro-inflammatory cytokines reduce protein synthesis and increase protein catabolism in muscle, induce synthesis of acute phase proteins in liver, and decrease de novo fatty acid synthesis and increase lipolysis in adipose tissue. In the central nervous system there is induction of fever, which increases metabolic rate, and induction of sickness behaviour. There are few reports in the literature of studies on the APR during gastrointestinal nematode (GIN) infection in sheep. However, IL-6 message is present in mucosa during Trichostrongylus colubriformis infection and mast cells in many species contain preformed TNFα. The changes in appetite, growth and nitrogen metabolism seen during GIN parasitism in sheep are in accord with the systemic effects of the APR. This review reports studies on activation of the APR in mastitis and fly strike, and the effects of APR on wool growth in high and low tensile strength genotypes and during Haemonchus contortus infection. The modified capacity of tissues to take up amino acids during pro-inflammatory cytokine perturbation of nutrient utilisation may limit the capacity for dietary supplementation to remedy the cost of host defence. Genetic variation may occur in production of pro-inflammatory cytokines or in tissue sensitivity to pro-inflammatory cytokines during GIN infection and may provide a basis for selection for resilience. Some questions for future research are identified.

Do carotenoids and spleen size vary with helminth load in greylag geese?

“…First, carotenoids may be more abundant because they are being concentrated in the tissues, especially the liver, to control physiological stress, so we are in fact measuring not carotenoid availability but rather the carotenoid requirements of the organisms. Helminth infection and other stressors induce catabolism of proteins in muscle and synthesis of acute-phase proteins in liver, and other metabolic changes (Colditz 2003) that can increase the demand for carotenoids in the liver. This interpretation conflicts with the view which is sometimes espoused that carotenoids are limiting in the environment (Endler 1980; see the discussion in Lozano 2001).…”

Adult Trichostrongylus colubriformis infection did not affect protein synthesis rate in whole-body, intestinal, hepatic and skeletal muscle tissues of lambs fed fresh Lucerne (Medicago sativa)

“…It is also a large component of the gastrointestinal tract where T. colubriformis comes into contact with the epithelium of the small intestine. Serum protein leakage, intestinal mucus production and intestinal cell exfoliation are some of the consequences of parasitic infections (Colditz 2003).…”

“…It is also a large component of the gastrointestinal tract where T. colubriformis comes into contact with the epithelium of the small intestine. Serum protein leakage, intestinal mucus production and intestinal cell exfoliation are some of the consequences of parasitic infections (Colditz 2003).These protein losses are likely to affect tissue protein turnover, particularly at the site of infection, and thus alter the amino acid (AA) requirements of the small intestine. …”

Fractional protein synthesis rate and polyamine concentrations in tissues of Merino sheep selected for gastrointestinal nematode resistance

“…If so, methionine oxidation must have been enhanced because decarboxylased methionine is a precursor (Seiler, 1990). In addition, a suggested extra demand for cysteine by increased excretion of mucins in the small intestines and antibodies for the expulsion of nematode larvae and adults (Harrison et al, 1999;Theodoropoulos et al, 2001;Colditz, 2003) may also stimulate methionine oxidation through the transsulphuration pathway (Finkelstein, 1990). It has been proved that oxidation of methionine occurs in the gastrointestinal tract of sheep, accounting for a 9% of whole-body methionine oxidation (Lobley et al, 2003).…”