Evaluation by Dog Growth of Egg Yolk Protein and Six other Partially Purified Proteins, some after Heat Treatment

Abstract

Six partially purified proteins and the protein of fresh raw egg yolk were compared for their growth-promoting value for purebred young cocker spaniel dogs. Two of the protein sources, casein and dried defatted whole egg, were fed both unheated and heated at 140° for 15 minutes before being incorporated in the diets. Lysine (l + monohydrochloride) and dl-methionine were added at 0.6% and 1.0% levels, respectively, to additional diets containing heated and unheated casein. All the egg diets were fed at a 12% level, all the casein diets, beef, peanut flour, gluten and egg albumin at the 18% level, and the gluten and egg albumin also at the 40% level. On the basis of gain per gram nitrogen intake in 120 days from beginning weights of 1.5 to 2.0 kg, the egg yolk produced the best growth. If the egg yolk protein index is taken as 100, the other proteins had indexes as follows at 18 or 12% levels: beef 76, defatted dried whole egg 75, casein 74, peanut flour 42, gluten 34, dried egg albumin 26. At the 40% level the gluten had the value 35 and the egg albumin 9. The heat treatment had little depressing effect on the casein, index 68, and the added lysine little reparative action, index 70. This may be due to the removal of lactose in the purifying process and the consequent prevention of a browning effect by heat. The value of the egg protein was decreased by heat treatment to 63. The addition of 1.0% methionine to the unheated casein led to depression of the protein index to 58. The average absorption of all heated proteins was lowered 15 to 21% below that of the corresponding unheated proteins, but the reduction in growth value was relatively small. The levels at which the egg and casein diets were fed had been found to be the minima on which normal growth could be obtained. The amino acid assortments absorbed from the heated diets were apparently at least as favorable to growth as were those of the unheated proteins. The egg albumin contained an active antitryptic substance which greatly reduced its absorbability and allowed very little growth. The gluten diets were well absorbed, as were the peanut flour and beef. The loss of nitrogen in the gluten and peanut flour-fed dogs was in the urine. The serum protein levels of the dogs on the heated diets and those on peanut, gluten and egg albumin were depressed, as were the albumin-to-globulin ratios on the heated egg, peanut, gluten and egg albumin. The hemoglobin levels were also low on these 4 diets. The tissues of all the dogs fed egg albumin were edematous and their livers were moderately fatty. The testes of the dogs at 200 days of age and over weighed significantly less per kilogram body weight in the animals on the heated diets. All the gluten-fed dogs had running fits and one died during a convulsive seizure. These observations are in contrast with the superior performance of rats and adult dogs fed egg albumin at low levels in other experiments.