The influence of heating on the nutritive value of soya-bean meal for ruminants.

I t has been generally assumed that the nutritive value of protein feeds for ruminant animals is not influenced by the chemical and physical properties of the proteins. Several recent investigations have shown that proteins with a high solubility are degraded in the rumen to ammonia at a rate too rapid for efficient utilization. The rumen micro-organisms can then utilize only a relatively small part of the liberated ammonia for synthetic purposes. Excess ammonia diffuses into the blood and is converted in the liver into urea, and most of this urea is excreted in the urine, only a small amount being returned to the rumen through the saliva. Evidence was given by El-Shazly (1958) and Jasiorowski (1960) that the protein in green forages and hays is utilized to a greater extent when it is of low solubility, highly soluble proteins from similar feeds being utilized to a lesser degree. The beneficial effect of reducing the solubility of protein in concentrates by heating was first recognized by Chalmers, Cutherbertson & Synge (1954) and Chalmers & Synge (1954), and confirmed by Whitelaw, Preston & Dawson (1961) who found considerable advantage in the use of heat-treated groundnut meal in comparison with untreated groundnut meal. I t is well known that the full utilization of soya-bean meal for poultry feeding is obtained only by proper heating. The causes generally recognized as responsible for the improvement of soya-bean meal by heat treatment are irrelevant for ruminants. Since the solubility of protein of soya-bean meal decreases considerably on heating, we compared the utilization by ruminants of protein of soya-bean meals subjected to different heat treatments. Preliminary experiments carried out in a miniature artificial rumen showed a very significant decrease in the amount of ammonia liberated from heated soya-bean meal in comparison with the untreated soya-bean meal. These results led us to examine the utilization by sheep of three different kinds of soya-bean meal, the rate of liberation of ammonia in the rumen, changes in blood-urea concentration and nitrogen balance being used for assessing their value.