Despite their widespread use in poultry diets, the ways in which enzym
es function are still not fully understood. Whilst it is agreed that a
reduction of intestinal viscosity is the most likely mechanism when t
he appropriate enzymes are used in barley- and rye-based diets, some a
nimal nutritionists claim that this is not so important in enzyme supp
lemented wheat-based diets. This paper, which attempts to place the re
levant pieces of information into context, indicates that, even in the
case of wheat-based diets, intestinal viscosity is a major factor lim
iting bird performance. Thus, in wheat fed birds the use of enzymes to
reduce intestinal viscosity is likely to be the most effective method
for improving performance. Data are also presented which, contrary to
popular belief, indicate that most of the beneficial effects resultin
g from the feeding of xylanase-based enzymes to broilers are observed
in the latter stages of the production cycle.