SYMPOSIUM ON ‘APPLICATION OF BIOTECHNOLOGY TO LIVESTOCK PRODUCTION’ Biotechnology and improvement of

Abstract

A high proportion of barley and wheat grown in Western Europe and maize in the USA is used as feed for livestock. When used for simple-stomached animals, such as pigs and poultry, the nutritional quality is limited by the low amounts of certain essential amino acids, and it is necessary to supplement the diet with sources of these amino acids for maximum growth. The definitive studies of Fuller et al. (1979a,b) have shown that barley is deficient in lysine, threonine and (marginally) histidine as feed for pigs, and it can be assumed that the same applies to wheat. For maize the limiting amino acids are lysine and tryptophan (Bressani, 1975). The present discussion will be restricted to barley, and will concentrate on studies from our own laboratory. We will also consider feed quality as the proportions of lysine and threonine in the grain proteins, although we appreciate that this definition ignores the important factor of protein digestibility. Furthermore, since lysine is the first limiting amino acid, and proteins which contain a high proportion are generally also rich in threonine (and vice versa), the emphasis will be on lysine content. The biochemical description of barley seed quality can be applied, with relatively minor alterations, to wheat and maize. However, because wheat is a hexaploid, the application of this information to improvement will be more difficult than with the diploids barley and maize.