Abstract. The aim of this study was to show how to adapt and convert the Mitscherlich model to animal nutrition studies in a theoretical way. The new form of the model was obtained by applying a mathematical conversion step by step to use the Mitscherlich model in an in vitro gas production or in in situ nylon bag studies which have an important role in animal nutrition. The parameter which is not included in new model but important for digestion was gained for the model. Moreover, it was shown how to obtain important digestion equations by using the new form of Mitscherlich model. Also the equation formulas were obtained for both with and without lag-phase. Consequently, it was shown how to convert a model, which is previously not used in terms of animal nutrition, into a different purposive form and how to obtain the new equations from this form step by step in a theoretical way. Besides, the new form of Mitscherlich model, which is an alternative to other models, will importantly contribute to the literature by obtaining some important equations not found in many of the other models.