Mean specific activity of hepatic microsomal CYP enzymes of chickens. A. Average amount of formaldehyde produced in aminopyrine N-demethylation assay (μmol per minute per mg microsomal protein), indicating the mean specific activity of hepatic microsomal CYP2H/CYP3A37 isoenzymes. B. Average amount of 4-aminophenol produced in aniline-hydroxylation assay (μmol per minute per mg microsomal protein), indicating the mean specific activity of hepatic microsomal CYP2H isoenzyme. Results of enzyme assays, carried out with the hepatic microsomal fraction of chickens after oral application of butyrate bolus at a lower (0.25 g/kg BW, n=10) and a higher (1.25 g/kg BW, n=9) dose or treated with intracoelomal phenobarbital (PB) injection (80 mg/kg BW, n=6), are compared to those of controls (n=9). Data are presented as mean ± SEM. **Significant difference, P<0.01.