Carbohydrate Composition in Relation to Pasture Quality

THE TERM “pasture quality” is a measure of the ability of the pasture to provide the nutritive requirements of the grazing animal. Many plant constituents contribute to this policy but only one group, the carbohydrates, will be considered here. At present probably the only reliable and meaningful method of assessing the relative nutritive value of different pastures is by comparing actual animal production on the pastures growing under identical conditions. Such a method is, of course, unsuitable for the plant breeder during the early stages of a plant breeding programme when he needs to select for quality from a large number of plant progenies. For this reason, it is desirable that quality be defined in more specific terms so that relatively simple tests for it can be devised. Work aimed at such a definition should, of course, be based on material from pastures whose animal potential is being measured at the same time. For this reason, work at Plant Chemistry Division on the possible role of the carbohydrate constituents in contributing to nutritive value has been based largely on material from single variety ryegrass pastures on which growth rate in sheep has been the index of animal production. The present account of how the plant carbohydrate composition of pasture can influence pasture quality will be illustrated with results obtained from these trials.