1. The digestibility of dry barley and acid-treated moist barley was studied with eight Friesian steers in two consecutive trials each of a duplicated, 2x2 factorial design. In the first trial the diet consisted of either dry or moist (30%) acid-treated barley in the rolled or whole form together with chopped hay; in the second trial rolled or whole, moist (24%) acid-treated barley was given with either chopped hay or silage.
2. No significant difference between the diets in dry-matter intake was observed in the first trial, but in the second trial there was a significantly greater (P< 0·001) intake of dry matter with the hay than with the silage diets.
3. For diets containing either of the moist barleys the digestibility of crude protein was higher when the grain was rolled than when it was whole, the differences being significant (P<0·05) for diets with the 24%-moisture barley. Dry-matter digestibility also was higher for diets containing rolled rather than whole, moist (24%) barley, the difference being significant (P < 0·05) for diets based on silage.
4. Digestibility of starch was significantly greater (P<0·05) when acid-treated moist (24 or 30%) barley was given in the rolled rather than the whole form. Differences in starch digestibility between whole and rolled dry barley were not significant.
5. For all diets the digestibility of crude fibre was greater when the barley was whole than when it was rolled, the difference being significant (P < 0·05) for diets containing hay.