The objective of the present paper was to verify whether the method of studying the anaerobic degradability of organic matter of excrements could reveal the utilization of dietary organic matter in the digestive tract of ruminants in relation to the lactation period, and whether it could be replaced by a cheaper and easier method of acid hydrolysis of excrements. Changes in anaerobic degradability and hydrolysis yields of excrements were investigated in an experimental herd of 30 cows divided into two groups differing in their lactation period by 30 days. The results document that anaerobic degradability is a suitable indicator of anaerobic digestion conditions in the digestive tract of animals and of the fitness of their organism. However, the results of excrement hydrolysis according to the Rovira and Val lejo (2002) method were hardly reproducible and so they could not be used, when only the very labile organic fraction is evaluated. The evaluation of the sum of very labile fractions and semi-labile fraction provides easily available values, but these are only orientative values that cannot replace the costly and labour-consuming determination of anaerobic degradability of excrements