Breeding for nutritive quality

Whilst herbage grasses and legumes are grown primarily to provide digestible energy and other nutrients for farm livestock, plant breeders have tended to concentrate on total or seasonal yield of DM, i.e. on the maximum fixation of energy by the crop, with any assessment of its nutritive value being left to a later stage of evaluation. In terms of providing the maximum amount of utilizable energy, together with the necessary levels of other nutrients, however, consideration should be given to the possibility of improving nutritive quality directly by breeding. The present paper outlines some of the problems involved in this approach and assesses the possibilities of breeding for nutritive quality. The first step is to identify those features of the crop which determine its nutritive quality. The provision of digestible energy is of primary importance; but protein or mineral content can also limit animal production, and in some herbage species the presence of harmful compounds, such as oestrogens, can pose problems. Information on the relative importance of these features may be obtained both from our knowledge of the nutritional requirements of the ruminant and from feeding or grazing trials, followed by attempts to identdy the physical or chemical basis of differences in animal performance. Following the identification of the most important nutritional components, the nutritionist and the breeder need to cooperate to develop rapid and reliable screening tests which can deal with the large number of small samples involved in a breeding programme. These screening techniques can then be used to develop material with the required nutritional characteristics, either by selection from within existing adapted varieties, or by introduction from wild ecotypes or even from other closely related species. Finally, the resulting selection lines or potential varieties must be critically assessed in terms of animal performance, under grazing or in indoor feeding trials or both (Cooper, 1973 ; Jones et al. 1974).