Evaluation of Protein Quality in Cottonseed Meals by Chick Growth and by a Chemical Index Method

Abstract

Twenty-three samples of cottonseed meals, made by different manufacturing processes, were evaluated by chick feeding tests. Wide variations in the protein quality of the meals made by each process were found. Low processing temperatures did not always produce high quality meals. Although the free gossypol content of most of the meals was quite low, the total gossypol content of the meals proved to be an important factor in determining the nutritional value of the protein. A relationship was found between the solubility of the protein in 0.02 N sodium hydroxide and the nutritional value of the meal. A chemical index which takes into account both total gossypol content and nitrogen solubility, in 0.02 sodium hydroxide, was devised for the chemical evaluation of protein quality in cottonseed meals. A good correlation was found between the chemical index values and chick growth rate. Lysine availability as determined by rat feeding tests proved be closely related to the values obtained for the meals by chick growth rate. Lysine supplementation of the poorer meals resulted in an increased growth rate of chicks amounting to over 100%. Lysine supplementation of the better meals resulted in some improvement in growth rate, but the percentage increase was less.