The article presents a study on the fiber effects on feces quality with the use of various celluloses that created a model to study the effect fecal dry matter and water excretion on fecal miniral excretion in dogs. The method used in the study was the effect of 6 cellulose types, microcrystalline versus fibrous, and a guar on fecal miniral excretion which was investigated in feeding trials with adult beagles. The results show that fecal dry matter excretion has a significant influence on fecal excretion of calcium, magnesium, and phosphorus.