Utilization of zinc from picolinic or citric acid complexes in relation to dietary protein source in rats

Young male Sprague-Dawley rats were divided in 18 groups of eight animals each and were fed ad libitum for 24 d a purified diet with 20% casein, whey protein or serum albumin as protein source. Each diet was supplemented with zinc picolinate, zinc citrate or zinc sulfate to a level of dietary zinc equal to 5 or 10 ppm. The source of zinc had no significant effect on zinc utilization with any of the three dietary proteins or at either dietary zinc concentration. With the 5 ppm Zn diet zinc concentration in the serum, but not weight gain or the zinc concentration in femur, testis or whole body was lower in rats fed the casein diet than in those fed the whey diet. Zinc concentrations in serum, femur, testis and whole body, but not weight gain, were lower in rats fed the casein diet than in those fed the serum albumin diet. With the 10 ppm Zn diet, zinc concentrations in serum, femur and whole body, but not weight gain nor zinc concentration in testis, were lower in rats fed the casein diet than in those fed either of the other diets. These results suggest that the reason for the lower utilization of zinc from cow milk in comparison to human milk may be the higher casein concentration in cow milk.