Effect of stocking density and sex on growth performance, meat quality, and intestinal barrier function in broiler chickens

The objective of the current experiment was to investigate the effect of stocking density and sex on growth performance, meat quality, and intestinal barrier function in broiler chickens. The experiment was conducted in a completely randomized design with a 2 x 4 factorial arrangement consisting of sex and four different stocking densities in battery cages. A total of 540 1-d-old Ross 308 broiler chickens were allotted to one of eight treatments with five replicates. Within each sex, birds were raised at four different stocking densities of 15.2, 20.2, 25.3, or 30.4 birds/m(2) from 1 to 28 d of age. Different stocking densities were achieved by raising a different number of birds per battery cage with identical floor size (0.76m x 0.78m). At the end of the experiment, two birds per replicate were euthanized by CO2 asphyxiation to collect tissue samples for further analyses. Results indicated that no interactions between sex and stocking density were observed for all measurements except for serum lipopolysaccharide (LPS) concentrations. Increasing stocking density decreased (linear, P<0.01) body weight gain and feed intake, but had no negative effects on meat quality. Trans-epithelial electrical resistance values, a measure of intestinal permeability, were decreased (linear, P<0.01) with increasing stocking density, regardless of sex. Accordingly, serum LPS concentrations were increased (linear, P<0.01) with increasing stocking density. However, increasing stocking density increased serum LPS concentrations in male broiler chickens, but had no effects on female broiler chickens, showing an interaction (P<0.01). The expression of zonula occludens-1 (ZO-1) and junctional adhesion molecule B (JAM-2) was decreased (linear, P<0.05) with increasing stocking density. In conclusion, increasing stocking density decreases broiler performance regardless of sex and this negative effect is likely associated with decreased intestinal barrier function.