Protein-zinc interrelationship in young rats

The purposes of this study were to determine if the presence of zinc could improve the utilization of dietary protein by young rats and if the response of young rats to zinc supplementation were affected by the level of protein in the diet. Criteria for evaluating animal responses to various test diets used in the study included weight gain, hemoglobin concentrations, and the levels of copper, iron, and zinc in the liver. Nine test diets, based on combinations of three levels of protein (7.5%, 15.0%, and 30.0%) and three levels of zinc supplements (0 ppm, 50 ppm, and 100 ppm) were used. Young rats were observed over a period of four weeks. Results indicated that all animals receiving the zinc deficient diets exhibited poor growth rates regardless of the level of dietary protein. The addition of zinc to the diets was associated with highly significant increases in weight gain. Maximum growth was obtained with 50 ppm of zinc added to the diet containing 15% protein. In the presence of adequate zinc, increasing levels of dietary protein were associated with highly significant increases in weight gain. Even when zinc was added to the diet containing a sub-optimal level of protein there was significant improvement in weight gain; thus there is indication that zinc improves the utilization of an inadequate level of protein in the diet. A highly significant zinc-protein interaction was also associated with growth data. Increasing the level of zinc above 50 ppm, however, appeared to have an advert, effect on protein utilization