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