The effect of zinc deficiency on the body composition of rats.

Body composition and the levels of some plasma metabolites were measured in zinc deficient and control rats with the aim of assessing the nature of the metabolic defects resulting from zinc deficiency. Two experiments, lasting 15 and 20 d, were carried out using 52 immature rats. Zinc deficient animals were fed a diet of 1-2 mg Zn/kg. Pair fed and ad libitum control rats received the same diet with 100 ppm zinc added to the drinking water. Feed intake and growth rate were measured, and the carcasses were analyzed for protein, fat, and ash. In each experiment, a group of rats were killed on d 1 to provide pretreatment values and to allow for estimates of net deposition of carcass components. Lactate, urea, and zinc were assayed in plasma, as well as zinc concentration in carcasses and liver. The main effect of zinc deficiency was to reduce feed intake and efficiency of feed conversion, resulting in a reduced proportion of carcass fat. However, when adjustments were made for difference in body wt because of the reduced feed efficiency, zinc deficiency per se resulted in an increase in the proportion of fat in the carcass. Plasma lactate concentration was unchanged, but urea concentration increased in both pair fed and zinc deficient rats relative to ad libitum fed control animals. The results indicate that a defect in protein synthesis and an increase in energy expenditure, perhaps resulting from increased protein turnover, underlies the reduced growth and efficiency of feed conversion of zinc deficiency.