Effect of leaching on apparent digestion coefficients of feedstuffs for salmonids

Fecal excretions were collected from rainbow trout (Salmo gairdneri) in metabolism chambers. In this method of collection the daily excretion is suspended in about 1 L of water. Aliquots of the suspension were separated into solid and liquid fractions by settling, centrifuging, or filtering. Solid and liquid fractions and the unseparated suspension were analyzed for total nitrogen. Digestion coefficients for protein were calculated on the basis of solids and on total suspension. More than half of the fecal nitrogen was in the liquid fraction. Digestion coefficients for protein based only on solids were about 10 percentage points higher than those based on the total suspension, apparently because of leaching when the fecal matter was exposed to water. Digestibility and metabolizable energy of 55 diet ingredients, obtained by the metabolism chamber method, were tabulated.