*2.2. Chemical Analysis*

The experimental diets and lyophilized digesta and faeces were ground in a grinding mill to pass a 0.5 mm sieve and analyzed for dry matter according to the Association of Official Analytical Chemists (AOAC) method by drying samples to a constant weight at 105 ◦C [28]. The same method was used for the estimation of dry matter in vitro and in vivo digestibility [28].

Trace mineral concentrations in the diets, faeces and digesta samples, filtrates, and/or supernatants were analyzed using a double-beam atomic absorption spectrophotometer (AA-7000 Series, Shimadzu Co., Kyoto, Japan). The microwave-assisted digestion method using closed pressure vessels (MWS 4 Speedwave, Berghof Co., Eningen, Germany) was used for the decomposition of the diets, faeces, and digesta samples [29].

Cr2O3 concentrations in faeces and digesta samples were analyzed using the colorimetric method of Kimura and Miller [30]. pH values in the digesta of duodenum, jejunum, and ileum and in in vitro buffers and mixtures were measured with the pH electrode of a digital pH meter (WTW InoLab pH Level 2, Weilheim, Germany).
