Feeding Livestock

CHEMISTS years ago developed methods by which they could analyze feeds and have the constituents sum to TOO percent. Chemists and physiologists concluded therefrom that protein, fats, carbohydrates, and certain mineral elements were the only nutrients animals required. Data from experiments made it clear, however, that the quality of the ration and its ability to promote growth could not be predicted accurately on the basis of its chemical composition. Animal husbandmen then began to speak of "specific effects of nutrients" to account for improved results when certain foods were included in the ration. Chemical studies later showed that proteins of different sources yielded different proportions of amino acids, the building blocks of proteins. It also became known that the different proteins varied in quality or biological value, an expression of efficiency for maintenance and growth of animal life, depending on the combination of specific amino acids. The amino acids subsequently were grouped as essential and nonessential. We now know the amino acid composition of proteins as determined chemically and microbiologically, and we can supplement deficient proteins with specific amino acids or with other proteins rich in the needed amino acids. The latter method is commonly used today in the feeding of livestock. The quality of protein or its biological value is not an important consideration in terms of the ruminant because the proteins largely are broken down and resynthesized into bacterial protein by the bacteria in the rumen. The bacterial protein is then utilized by the ruminant. Thus, if an essential amino acid is missing in the original protein, it will be synthesized by the rumen bacteria and thus become available to the ruminant. Even synthetically produced urea, a nonprotein source of nitrogen that contains no amino acids, can be utilized by the rumen bacteria to synthesize amino acids and bacterial protein. The use of urea as a substitute for part of the ''protein source" for ruminants has been one of the important advances of the century in animal feeding. Recognition of the importance of calcium and phosphorus for bone formation and of common salt in the diet of animals dates back many years, but the real needs and functions of calcium, phosphorus, sodium, and chlorine began to be understood less than loo years ago. Then came the recognition of the essential nature of