Digestibility of dry matter, protein, starch and lipid by cod, Gadus morhua:: comparison of sampling methods

Atlantic cod were fed 11 different extruded diets spanned by a multiple simplex design. The dietary ranges of protein, fat and starch were 36-66%, 8-28% and 8-18%, respectively. All diets contained 0.1% yttrium oxide as an inert marker. After several months of feeding, faeces were sampled, either by stripping or by dissecting the last part of the intestine, which in turn was frozen and faecal matter removed while still partly frozen. No significant differences were found in average digestibility results of dry matter, protein, starch or lipid when comparing the two methods of sampling. All groups showed high digestibility of dry matter, protein and lipid, with minor variations, and only extreme feed compositions resulted in changed digestibility of dry matter and protein. A larger variation was found in apparent starch digestibility, from 60% to 90%, however, independent of dietary level when this was below 17% of dry matter, in agreement with findings for this nutrient as concerns other carnivorous fish. No difference was detected for any of the compared digestibility coefficients when evaluating the four centre points of the multiple simplex design. In conclusion, no difference between methods gives the opportunity to freely choose sampling method, and either stripping or dissection of faecal matter can be used to determine apparent digestibility values in cod. (C) 2003 Elsevier Science B.V. All rights reserved.