Ther.e are no unifying criteria of vitamin requirements in poultry. All vitamins
serve different functions so it is necessary to consider the metabolic role
of each before deciding upon the most appropriate criteria. These are usually
the commercially important aspects of performance rather than biochemical
indices. By and large, the latter are not well developed, although in some cases,
such as biotin (Whitehead and Bannister, 1980), the response of a vitamin dependent enzyme has been shown to parallel the response of growth to dietary
increments of the vitamin.