Therefore heat treatment exerts some negative impact on phytate degradation (Reale et al., 2007). Unfortunately, naturallyoccurring thermostable phytases have not been found yet. Normally, phytases undergo denaturation between 56◦C and63◦C (Lehmann et al., 2000). In our experiment the phytases naturally occurring in wheat bran are expected to be still activeafter fermentation due to the low temperatures applied for drying. However, during the extrusion of bran, temperaturesup to 155◦C were reached thus leading to the denaturation of endogenous phytases. The level of Ca in the feed mixturescomprised a proportion from wheat bran itself (1.7 g kg−1) and the added calcium carbonate as the major part. All groupshad identical Ca intake, but the CTTAD values were different. One possible explanation is, that the amount of Ca absorbedform calcium carbonate was promoted in the fermented bran feeding group. According to Selle et al. (2009), a lower phyticacid content, as induced by phytases, reduces the ability of phytate to chelate Ca, and this results in a higher availability inthe small intestine. Similar results were reported by Rojas and Stein (2012), who additionally assumed that a minor part of