DIETARY SOYBEAN PROTEIN DECREASES PLASMA TAURINE IN CATS

Commercial dry and canned diets fed to cats cause similar to two- and fourfold increase in the taurine requirement, respectively, as compare d with that observed for purified diets. In two experiments, the effec t of source and level of protein and fiber in the diet on the concentr ation of taurine in plasma and whole blood of cats was studied. All di ets contained 1 g taurine/kg dry matter. When a casein-based diet cont aining either 25% or 50% protein was given to cats for 6 wk, no differ ence in plasma taurine concentration was observed; however, substituti ng soybean protein for casein resulted in a significant (P < 0.01) dec rease in plasma taurine concentration of cats in the 50% soybean prote in group, but not in the 25% soybean protein group. In Experiment 2, t he 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 pro tein or casein diets had significantly lower plasma taurine concentrat ions than cats fed a 30% casein diet, with the 60% soybean protein die t causing the greater decrease. There was no effect of either 2 or 4% soybean fiber on plasma taurine concentration as compared with the sam e diet without the added fiber. The taurine concentration in plasma wa s 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 c oncentration. Cats given diets containing 60% casein or soybean protei n diets excreted a greater amount of fecal total bile acid and total t aurine than cats given a 30% casein diet. Cats with higher plasma conc entrations of taurine excreted a greater amount of free taurine in uri ne, and a lesser amount of taurine and bile acids in feces. These resu lts show that although protein source (soybean protein) and the quanti ty in the diet have a significant effect on the excretion pattern of t aurine by cats, these effects are not sufficient to account for the ma rked increase in the taurine requirement found when canned heat-proces sed diets are fed.