2.2. Analytical procedures
Dry matter (DM) content of feed and feces was determined by drying the samples at 60 1C for 48 h in a forcedair oven. Crude ash was determined after combustion at
525 1C for 6 h in a muffle furnace. Content of OM was
determined as the difference between DM and crude ash.
Nitrogen content was determined according to the Dumas
method described by Hansen (1989). Crude fat was determined by hydrochloric acid hydrolysis followed by extraction in petroleum ether according to Stoldt (1952). In vitro
OM digestibility was determined by incubating samples
anaerobically in ruminal fluid and a buffer solution for
48 h in glass tubes at 38 1C, followed by incubation in a
pepsin HCl solution for additional 48 h at 38 1C according
to Tilley and Terry (1963). Starch content was determined
enzymatically by means of α-amylase according to Bach
Knudsen et al. (1987). Samples were destroyed by a dry
ash method (450 1C for 3 h) before determination of P
content in feed and milk. Content of Na, K, S and Cl
was analyzed in feed samples after the same procedure
followed by spectrophotometric analysis. Phosphorus content was determined by the ammonium vanadate method
as described by Stuffins (1967).