Determination of digestibility of commercial salmon feeds

The aim of the study was to develop an applicable method for determination of the digestibility of nutrients in commercial feeds. Leaching of markers and dry matter (DM) were compared between a commercial extruded feed contai ning La2O3, the same commercial feed coated with oil and other additional m arkers, and the commercial feed that had been ground and re-pelleted with w ater, marker and a crude alginate binder. Two markers, Y2O3 and Cr2O3, were added in both the coated and the moist feeds. The optimal inclusion level of binder and water to minimize the leaching of DM from the moist pellet wa s determined in a preliminary study. The lowest leaching of DM was achieved with the inclusion of 2% alginate and 35% water. Added markers tended to b e less homogeneously included in the coated feed than in the moist feed, an d the markers leached relatively more than the DM from the coated feed. App arent digestibility coefficients (ADCs) of DM, fat, nitrogen (N), energy, o rganic matter (OM), and phosphorus (P) in the commercial dry feed and the m oist feed were compared in two experiments with Atlantic salmon. Difference s between the ADCs in the two experiments were observed for N and P. The AD C estimates of the moist feed were slightly lower than those of the dry fee d for all nutrients. Similar ADC estimates for each nutrient were obtained for all markers, except for Y2O3 which produced a slightly higher ADC for N than did La2O3. By using the moist feed method recommended from this study , a difference of about 1.4% units in ADC of energy and of 0.8% units for N between the original and the modified test feed was demonstrated. This mea ns the error of ADC estimates is low compared to using fixed digestibility coefficients for each of protein, fat and carbohydrate, a method that has b een employed for declaration of commercial fish feed. Further development o f the method is discussed. (C) 1999 Elsevier Science B.V. All rights reserv ed.