The use of brewery by-products which contain varying quantities of live and dead yeast cells as nitrogen supplements in diets for ruminants is well documented.

There have been several recent reports of micro-organisms, previously considered as being totally aerobic, multiplying and exhibiting growth in the rumen and in rumen simulators and conferring beneficial effects on cellulolysis and growth or productive capacity of the animal. Dawson (1987) reported that certain strains of yeast (Saccharomyces cerivisae) multiplied when introduced into the rumen. Although at some point extensive lysis occurs with extrusion of the cell contents (Bruning and Yokoyama, 1988). The present experiment was carried out to assess the effects of including yeast culture (YS) (Saccharomyces cerevisae, plus growth medium: 5x106 organisms/g) in diets for ruminants. The responses in terms of effects on rumen metabolism were monitored in three cannulated steers.

The aim of the experiment was to determine the effects on the rumen metabolism and the degradability of a forage using the nylon bag technique (Ørskov and McDonald, 1970) when yeast culture was added to two contrasting diets and given to young steers. The diets were either a high forage diet of hay or a mixture of forage plus concentrate given in such a manner as to induce a negative associative effect.