The effect of variety, type of straw and ammonia treatment on digestibility and growth rate in steers

Abstract

The gross energy content of cereal straw is almost as high as that of grain, but, because straw is relatively indigestible even to ruminants, much of this energy passes right through the digestive system and so makes no contribution to nutrition. Treatment of straw with alkali (normally ammonia or sodium hydroxide) improves digestibility and thus increases the amounts of energy available to animals. Straw which has been improved in this way is often said to be of similar nutritional value to medium quality hay; but responses in terms of animal performance demonstrate that this is not always so.It has been observed that the nutritive values of straws of the various cereals and of the varieties within each cereal differ considerably and that, though alkali treatments generally improve the least digestible straws the most, the differences between improved straws may still be large enough to be important. Degradability measurements carried out on large numbers of wheat, barley and oat straws to obtain an indication of nutritive value, confirm this (Tuah et al. 1986), but further evidence was needed using feeding trials with animals to support these findings and demonstrate their practical significance.