Value of yeast protein for poultry feeds.

Evaluation of yeast as a main source of protein to replace fish meal or soybean meal in chicken feeds was reviewed in the attempt to establish another source of protein in chicken nutrition. Various substrates used for yeast growth were compiled. The chemical composition and vitamin B content of yeasts were summarized. Amino acids and nucleic acids of yeasts as well as net protein utilization, true digestibility, biological value, and protein efficiency ratio of yeasts and other protein foods were discussed to ascertain the nutritive value of yeast proteins. The results of studies conducted under practical conditions where yeasts were used to replace the extracted soybean meal and fish meal individually or together in commercial feeds were tabulated in detail in terms of growth, feed intake, feed conversion ratio, etc. It appeared that the growth of broilers fed the feeds containing yeast at a level of up to 15 to 20% was almost identical when yeast was added in place of soybean meal, but somewhat retarde...