Effects of dietary protein quantity and quality on the growth of dogs and rats

The growth of immature beagle dogs and weanling rats fed dietary protein concentrations between 0 and 20% were investigated. With lactalbumin as the protein source, 8- to 10-week-old dogs exhibited optimal growth when the diet supplied between 15 and 20% protein, whereas in older growing dogs (13-17 weeks) maximum growth and feed efficiency occurred with 11.7% dietary protein. Growth and feed efficiency of weanling rats were calculated to be optimal at 11.5% dietary protein. The protein efficiency ratio (PER) calculated during 14 days of feeding a 10% lactalbumin diet was 3.14 for 8- and 10-week-old dogs, 3.42 for 13- to 17-week-old dogs and 3.92 for weanling rats. Subsequent experiments examined the utilization of casein, soy isolate and wheat gluten by immature dogs and weanling rats. When diets contained 10% protein the adjusted PERs of casein, soy and wheat gluten were 2.50, 1.26 and -0.43 for the dog and 2.50, 1.60 and 0.34 for the rat, respectively. At 7.5% protein the adjusted PERs of casein, soy and wheat gluten were 2.50, 1.19 and -3.21 for the dog and 2.50, 1.44 and 0.29 for the rat. Thus, the rat can be a useful model for examining the quality of proteins fed to dogs. However, by using the rat one may overestimate the value of some low quality proteins.