Introduction

The range of avian diets is quite varied, and amongst the avian species there are omnivores, carnivores and herbivores. In common with other vertebrates, and indeed all nutritional heterotrophs, the diet provides both a source of energy and the necessary building blocks with which to generate new cell materials and to replace existing materials. The nutrients required by an organism fulfil these roles. Much of the study of nutrition is aimed at defining the nutrients in chemical terms; some of these are required in large quantities whereas others are micronutrients. The study of vertebrate nutrition, which was the focus of much biochemistry for the early part of this century, was carried out mainly using laboratory mammals and humans; interest in other vertebrates, especially birds, generally arose later. However, this was not always so, for example the discovery by Christiaan Eijkman in 1887 of polyneuritis in chickens fed a diet of polished rice that lacked thiamin (see Carpenter & Sutherland, 1994) and the discovery of vitamin K by Dam in 1935 as the factor that could overcome the slow blood clotting in chickens fed certain diets are cases where the avian work provided the lead.

Since the 1940s, nutritional science has been neglected by the majority of biochemists; the basic nutrients of the diet have been defined and in most cases their biochemical role is known, but, as Kornberg (1989) points out, we still lack detailed knowledge on (i) the optimum amounts of the constituents of food necessary to maintain health, (ii) the effects of dietary imbalances, and (iii) the effects of diet on disease.