Derivatization was performed using OPA (o-phthalaldehyde and
3-mercaptopropionic acid and FMOC (9-fluorenylmethylchloformate).
Separation of amino acids was conducted on a hypersil ODS
5 μm (200×2.1 mm) column, protected by a hypersil ODS
(20×2.1 mm) guard column. A Microsorb column (100-3 C18,
100×4.6 mm, Varian, Lake Forest, CA) was used for analysis of
cystine. Diets and fecal samples were analyzed for chromic oxide
(Cr2O3) according to Furukawa and Tsukahara (1966).
Apparent digestibility coefficients for dry matter (ADMD), protein
(APD), and amino acids (AAAD) of each diet were calculated using the
following equations (Cho and Slinger, 1979):