Effects of xylanase supplementation on performance, total volatile fatty acids and selected bacterial population in caeca, metabolic indices and peptide YY concentrations in serum of broiler chickens fed energy restricted maize–soybean based diets

The effects of xylanase supplementation on production performance, carcass traits, caecal volatile fatty acid and peptide YY concentration in serum of broiler chickens fed maize–soybean based diets were tested in a 42 d experiment. Dietary metabolizable energy (AME, N uncorrected) was decreased in the experimental diets by 0 (E1), 230 (E2) and 420 kJ/kg (E3). Each of these diets was supplemented with 0 (X1) or 16,000 units/kg (X2) of a commercial xylanase. The objective was to ascertain if the xylanase could spare dietary energy for growth through its effects on peptide YY concentration in blood. Reduction of dietary AME depressed body weight gain (P=0.014), deteriorated feed conversion ratio (P=0.018) and decreased carcass yield (P=0.0001) over 42 d. Irrespective of the level of supplemental xylanase, breast meat yield was the poorest in the E2 groups (P=0.003). Supplementation of xylanase had no effect on body weight gain, feed consumption, feed conversion ratio (feed consumption: body weight gain) and carcass traits (P>0.05). Low energy diets increased total volatile fatty acids (VFA) in caeca (P=0.0001). Xylanase supplementation tended to decrease caecal VFA irrespective of dietary AME (P=0.07). Increasing dietary AME reduced Salmonella (P=0.018) and Escherichia coli (P=0.019) and increased Enterobacteriaceae (P=0.012) populations in caeca. Reduction in dietary AME decreased glucose (P=0.0001) and cholesterol (P=0.012) in serum, particularly in the E3 groups. Serum glucose increased due to xylanase supplementation in the E1 and E3 groups but not in the E2 group (energy × xylanase P=0.0001). Supplementation of xylanase to the E2 groups decreased serum cholesterol as compared with the E1 and E3 groups (energy × xylanase P=0.002). On the other hand, xylanase supplementation decreased serum concentrations of protein in the E1 and E2 groups (energy × xylanase P=0.0001) and uric acid in the E2 and E3 groups (energy × xylanase P=0.006). Serum insulin reached a maximum (P=0.0001) in the E2 group irrespective of xylanase supplementation and added xylanase increased serum insulin (P=0.0001) at all dietary AME levels. There was an interaction between dietary AME and supplemental xylanase on serum peptide YY concentration (P=0.0001) which suggested that the xylanase induced increase in the serum peptide YY concentration was dependent on dietary energy density. It was concluded from the present investigation that supplementation of xylanase to a maize–soybean based diet of broiler chickens may consistently increase serum peptide YY concentration and improve metabolic indices like serum insulin levels. However, the results also indicated that with maize–soybean based diet, such positive effects on metabolic indices may not translate into performance if the diet is compromised with energy by 230 kJ/kg or more.