The effect of artificial drying on the energy value of grass.

From the results of a large series of calorimetric studies with artificially dried grasses (Armstrong, 1964), it was found that the value of a dried grass as an energy source for sheep could be predicted from considerations of its species and its chemical composition (Armstrong, Blaxter & Waite, 1964). The question arises whether the nutritive value of fresh grass can be inferred from that of dried grass, and whether the conclusions drawn for dried grass apply equally to fresh. There is evidence that the apparent digestibility of grass is slightly impaired by artificial drying (Dijkstra, 1956). Work in New Zealand (Johns, 1955; Christian & Williams, 1957), in Switzerland (Prabucki, 1963 ; Prabucki & Crasemann, 1961) and in this country (El-Shazly, 1952) has drawn attention to small differences in composition as between rumen liquor in sheep given fresh or frozen grass (frozen grass being regarded by Swiss workers as synonymous with fresh grass) and the rumen liquor of sheep given artificially dried grass or hay. The only study of the effect of artificial drying of herbage on its value as an energy source that we have traced is that by Heinzl (1944). Heinzl found that artificial drying of herbage resulted in a reduced energy retention estimated from the retentions of carbon and nitrogen when sheep were given supplements of fresh or dried grass. The experiments now described were made to find whether the energy of the same sample of grass was utilized differently when fresh and when dried.