Since Osborne & Mendel [1919] found that rats thrived when given a diet containing brewer's yeast as sole source of protein, many investigators have further studied the nutritive value of yeast protein. Plimmer, Rosedale, Raymond & Lowndes [1934], in experiments on chickens, and Mitchell [1924a] in experiments on rats, found that yeast protein, when it is the sole source of nitrogen in the diet, is intermediate in nutritive value between the high value animal proteins and the poorer vegetable proteins; Thomas [1909; 1910], from some experiments carried out on himself, had earlier come to a similar conclusion. Of particular interest are the experiments of Kon & Markuze [1931]; they showed that yeast protein supplements white bread protein in the nutriti'on of the rat. Trials of the value of yeast as a protein concentrate for the feeding of stock animals have all shown it to possess high nutritive-value. For milk production dried brewer's yeast is as good as linseed cake [Barton, Ness & Crampton, 1926], or ground nut cake [Kieferle & Dusch, 1932] or soyabean meal [Biinger, 1934]. In experiments summarized by Bunger [1939] dried cultired yeast (Torula utilis) was found to be but little inferior to fish meal for fattening pigs, when fed with some cereal and potatoes or other root crop. Many other workers have found brewer's yeast,to be a good protein concentrate for pigs. The available information on the value of yeast for egg production and chicken rearing is less accurate but dried yeast appears to be about equal in value to dried skimmed milk. The present experiments were designed to find the value of yeast protein as a supplement for cereal protein. The pig was the experimental animal chosen and maize the cereal. Comparison was made with the value of casein as a supplement for the proteins of whole maize. METHODS The 24 pigs used were of the Large White breed from the pedigree herd of the Agricultural Research Council Field Station, Compton. From the time of weaning until the young pigs attained about 20 kg. body weight they were given a commercial pig feed. They were then divided into eight groups of three pigs each, according to the diets they were to receive. For practical reasons it was not found possible to put all the animals on experiment at the same time; 15 animals were first procured and divided to make up groups 1, 2, 4, 6 and 7; later six pigs were received and these comprised groups 5 and 8; finally, three additional pigs were allocated to group 3. The sex, age at the beginning of the experiment and litter number of all the pigs are included in Table 3. Each group was housed separately in a large loose box which opened into a large uncovered yard. Both box and yard had sloping floors, and, as it was considered unwise to use bedding which the animals might eat, wooden boards were provided on which the animals could lie. The pigs had access to fresh water. The individual method of feeding was employed, the animals being fed to the extent of their appetites morning and evening. To prevent scattering, th...
