Protein as a Carbohydrate Precursor in the Chick

Abstract

Experiments were conducted to study the effectiveness of extra protein in promoting growth of chicks fed “carbohydrate- and glycerol-free” diets. Diets containing 15.4, 13.2 and 11.0 kcal metabolizable energy/g protein were fed. Results indicated that the requirement of the chick for carbohydrate can be met by protein but that the protein mixture used (soybean protein, methionine and glycine) was much less efficient than glucose in meeting this requirement. Pair-feeding studies were conducted to determine whether chicks fed “carbohydrate- and glycerol-free” diets divert amino acids from protein to carbohydrate synthesis. Results showed that little protein was diverted from protein to carbohydrate synthesis when protein was supplied by a mixture of soybean protein, methionine and glycine. Protein retention with and without supplemental glucose was 52 and 50%, respectively. However, deletion of excess glucogenic amino acids from the diet by replacing protein with a mixture of amino acids resulted in a marked reduction in nitrogen retention and growth which was overcome by the addition of glucose. These results indicate that excess glucogenic amino acids in soybean protein contribute to the carbohydrate requirement of the chick. The ability of the chick to synthesize carbohydrate from fatty acids, if present at all, is extremely limited.