Because wheat comprises such a large component of poultry diets, its n
utritional characteristics and, in particular, its metabolizable energ
y (ME) content are critically important. This paper examines the popul
arly held view that the ME of wheat is variable by seeking out composi
tional factors which could account for the variation. The bioassays wh
ich have been applied to the derivation of the ME of wheat have also b
een appraised and it has been concluded that substitution techniques w
hich are used in apparent ME studies may have contributed to the uncer
tainty which has been attributed to the ME value of wheat. Neither the
variety nor the site of its cultivation appeared to affect the ME of
wheat, but both density (positively) and ol-amylase activity (negative
ly) were correlated with ME; however, neither effect was large and the
commercial significance is doubtful. Attention has recently focused o
n the nonstarch polysaccharides in wheat, specifically water-soluble a
rabinoxylan, and response experiments after xylanase addition to wheat
-based diets have produced evidence that the viscosity of the digesta
is a factor resulting in poor performance; the mechanisms involved hav
e not, however, been elucidated.