1. Four growth trials were carried out with 297 group-fed steers given diets based on barley, minerals and vitamins, unsupplemented or supplemented
with either soya bean meal or various sources of non-protein nitrogen.
2. Steers given unsupplemented barley (11% crude protein in dry matter) had inferior growth rates up to 300 kg live weight but thereafter were equal to those given barley supplemented with urea in the drinking water or soya bean meal.
3. There were no significant differences in the growth rates of steers given barley supplemented with soya bean meal and those given barley supplemented with ammonium and mineral salts of formic acid or a mixture of acids (predominantly acetic).
4. In two out of three trials, tenth-rib joints from steers given barley supplemented with ammonium salts of mixed acids contained less fat and more protein and water than those from steers given barley supplemented with soya bean meal or proprietary protein supplements.
5. A number of possible explanations for the apparent carcass differences is discussed.