Dietary Soybean Protein Decreases Plasma Taurine in Cats

Abstract

Commercial dry and canned diets fed to cats cause ∼two- and fourfold increase in the taurine requirement, respectively, as compared with that observed for purified diets. In two experiments, the effect of source and level of protein and fiber in the diet on the concentration of taurine in plasma and whole blood of cats was studied. All diets contained 1 g taurine/kg dry matter. When a casein-based diet containing either 25% or 50% protein was given to cats for 6 wk, no difference in plasma taurine concentration was observed; however, substituting soybean protein for casein resulted in a significant (P < 0.01) decrease in plasma taurine concentration of cats in the 50% soybean protein group, but not in the 25% soybean protein group. In Experiment 2, the food intake of cats was limited [26 g dry matter/(kg body weight·d)], and the protein was 30 or 60% of the diet. Cats fed 60% soybean protein or casein diets had significantly lower plasma taurine concentrations than cats fed a 30% casein diet, with the 60% soybean protein diet causing the greater decrease. There was no effect of either 2 or 4% soybean fiber on plasma taurine concentration as compared with the same diet without the added fiber. The taurine concentration in plasma was higher (P < 0.05) in male cats than in female cats. Protein source, amount in the diet and gender did not affect the whole blood taurine concentration. Cats given diets containing 60% casein or soybean protein diets excreted a greater amount of fecal total bile acid and total taurine than cats given a 30% casein diet. Cats with higher plasma concentrations of taurine excreted a greater amount of free taurine in urine, and a lesser amount of taurine and bile acids in feces. These results show that although protein source (soybean protein) and the quantity in the diet have a significant effect on the excretion pattern of taurine by cats, these effects are not sufficient to account for the marked increase in the taurine requirement found when canned heat-processed diets are fed.