Abstract
Effect of immune stimulation and stocking density on growth, immunocompetent organ weight and plasma alpha 1 acid glycoprotein (AGP) concentration was studied in male broiler chicks to develop a laboratory model for studying a chronic immunological stress. Sephadex (G-50, 250mg/kg BW) and/or Escherichia coli lipopolysaccharide (LPS, serotype 0127: B8 500μg/kg BW) were used as agents to stimulate the immune system. Chicks were reared in two different stocking densities (217 and 650cm2 per chick) in experiment 1, and kept at 650cm2 per chick in experiment 2. In experiment 1, injection of Sephadex alone every other day over 10 days tended to reduce body weigh gain as compared to a saline injected control, but the effect was not significant. Injections with Sephadex and LPS on alternate days over 10 days significantly reduced body weight gain in chicks kept at 650cm2 per chick. In experiment 2, injections of LPS and Sephadex on alternative day over 5 days significantly reduced body weight gain and feed consumption. Relative spleen weights were higher in the chicks treated with LPS and Sephadex than those in the control chicks in both experiments. Alternate injections of LPS and Sephadex, or Sephadex injection alone increased AGP concentration in plasma in both experiments. The results suggested that injection with Sephadex and LPS on alternate days over 5 days mimics responses to a chronic stress such as reduction in growth and feed utilization, enlargement of liver and spleen, and activation of certain inflammatory responses. This laboratory model could be a useful way for finding novel nutrient(s) to alleviate the decreased rates of body weight gain and feed consumption by immunological stress.
