Performance and immune responses to dietary β-glucan in broiler chicks

Abstract

During the first week posthatch, the avian immune system is immature and inefficient at protecting chicks from invading pathogens. Among immunomodulators, beta-glucans are known as biological response modifiers due to their ability to activate the immune system. Current research suggests that beta-glucans may enhance avian immunity; however, very little is known about their influence on regulation of immune function. A study was performed to evaluate the effects of dietary beta-glucan on growth performance, immune organ weights, peripheral blood cell profiles, and immune-related gene expression in the intestine. One-day-old chicks were fed a diet containing 0, 0.02, or 0.1% yeast beta-glucan (n = 30/treatment). On d 7 and 14 posthatch, body and relative immune organ weights were measured and small intestinal sections were collected to evaluate gene expression by quantitative real-time PCR. Peripheral blood samples were also collected to determine heterophil:lymphocyte ratios. Supplementation of beta-glucan did not significantly affect BW gains, and no significant differences were observed among groups for relative immune organ weights or heterophil:lymphocyte ratios. Compared with controls, expression of interleukin (IL)-8 was downregulated in the beta-glucan-treated groups on d 7 and 14. On d 14, beta-glucan inclusion resulted in increased inducible nitric oxide synthase expression. Expression of IL-18 was upregulated on d 7 but reduced on d 14 due to beta-glucan supplementation. On d 7, interferon-gamma and IL-4 expression decreased in the beta-glucan-treated groups. However, on d 14, IL-4 expression was upregulated in the supplemented groups. Intestinal expression of IL-13 was also downregulated in the beta-glucan-treated birds on d 7. These results suggest that dietary inclusion of beta-glucans altered the cytokine-chemokine balance; however, it did not elicit a robust immune response in the absence of a challenge, resulting in no deleterious effects on performance.

Glucans and the Poultry Immune System

“…β-glucan supplementation has been shown to alter the cytokine profiles of unchallenged, day-old chicks (Cox et al, 2010). Compared with unsupplemented controls, broiler chicks receiving β-glucan from Saccharomyces cerevisiae were shown to down-regulate IL-8.…”

“…This enzyme results in the production of nitric oxide which reacts with superoxide anions to generate toxic derivatives which allow the macrophage to kill several types of pathogens. Cox et al (2010) reported upregulation of iNOS in response to β-glucan supplementation, implying increased capacity of macrophages to destroy pathogens.…”

“…Macrophages can also produce IL-8 (sometimes referred to as CXCLi2), which is a chemokine that is an important mediator of the innate immune system. Its primary function is to induce the migration of its target cells to inflammation sites (Cox et al, 2010). IL-18 is a pro-inflammatory cytokine largely produced by macrophages.…”

“…It primarily targets Th cells which will then secrete interferon-Ɣ. IFN-Ɣ plays an essential role in activating macrophages (Cox et al, 2010).…”

“…Compared with unsupplemented controls, broiler chicks receiving β-glucan from Saccharomyces cerevisiae were shown to down-regulate IL-8. The down-regulation of the IL-8 gene with β-glucan supplementation suggests that the β-glucan functions as an anti-inflammatory immunomodulatory (Cox et al, 2010). Cox et al (2010) were the first to report on the effects of dietary β-glucan on IL-18.…”