Physical form of the diet in relation to rumen fermentation.

This paper deals principally with alteration to the physical form of forage diets and the effect on rumen fermentation. When a forage crop is cut and conserved there are possibilities of (a) changing the physical and chemical characteristics of the forage before it is given and (b) of combining the forage with other food components. T o produce a ruminant ration of high nutrient potential both these measures should be based on nutritional principles. Information on mixed diets is limited (Topps, Kay & Goodall, 1968; Topps, Kay, Goodall, Whitelaw & Reid, 1968; MacRae & Armstrong, 1969; Nicholson & Sutton, 1969). Lack of space precludes in this paper adequate examination of the effect of physical form of cereals (Armstrong & Beever, 1969) and of cereal straws (Lamming, Swan & Clarke, 1966; Pickard, Swan & Lamming, 1969; Swan & Lamming, 1970) and, also, liquid diets (IZlrskov, Fraser & Corse, 1970) on rumen fermentation, and the paper has therefore been restricted to forage diets. T h e choice of title for this symposium is appropriate, and timely. However, posing the problems of manipulation and control of rumen fermentation does highlight the question ‘Manipulation to what end?’. Manipulation of rumen fermentation relates not only to the rumen but also to the host animal, the producing ruminant; the objective in controlling and manipulating rumen fermentation is to improve the efficiency with which the host animal utilizes its food for productive purposes. The physical form, and in particular the particle size, of dried forages can be altered markedly from the original long or chopped form. In addition to grinding and pelleting, dried chopped forage may be compressed into wafers or cobs, forms which are intermediate between chopped and pelleted. Methods are available to define the effects of processing on particle size (American Society of Agricultural Engineers, 1967) but are too seldom used. Earlier work has been reviewed by Minson (1963), Moore (1964) and Meyer, Kromann & Garrett (1965). Quantification of fermentation within the rumen, and throughout the alimentary tract, is possible with the use of ruminant animals fitted with cannulas at the abomasum, duodenum and other parts of the tract (Hogan & Phillipson, 1960; Ash, 1962; Brown, Armstrong & MacRae, 1968). Although there are limitations, principally of technique, to a more exact understanding, and therefore control, these preparations do permit the study of rumen fermentation in vivo.