Digestibility of protein, amino acids and starch in mink (Mustela vison) fed diets processed by different extrusion conditions

An experiment was carried out to evaluate the effect of different extrusion processes on digestibility of a fish-meal-based diet fed to mink. The feed was processed in a twin-screw extruder with the exit temperatures of the meal of 100, 125 or 150degreesC. Feed production was carried out three times, using different extrusion conditions to achieve the target temperatures. An untreated meal mixture was included as a control diet. True digestibilities of crude protein and total amino acids were lower for diets extruded at 125 and 150degreesC than for the control (P < 0.05). Digestibilities of crude protein, total amino acids, and the amino acids alanine, arginine, aspartic acid, cysteine, glutamic acid, histidine, isoleucine, leucine, lysine and valine decreased when increasing extrusion temperature from 100 to 125degreesC (P < 0.05), a further increase in temperature did not influence digestibility (P > 0.05). The highest reduction was seen for cysteine (6.8 percentage units). Starch digestibility was increased by extrusion, but there was no effect of temperature (P > 0.05). Digestibilities of crude protein, total amino acids, alanine, arginine, aspartic acid, glutamic acid, glycine, proline, histidine, lysine, tryptophan and valine were affected by the processing method (P < 0.05), which, by multivariate analysis, was revealed to be associated mainly with processing parameters: revolutions per minute, conditioner temperature, die temperature and feeding rate. Digestibility of starch was influenced mainly by the addition of water.