Fractionation of wheat distiller's dried grains and solubles using sieving increases digestible nutrient content in rainbow trout

Distillers’ dried grains with solubles (DDGS) from maize and more recently wheat contain moderate levels of protein at an economical cost. However, they also contain high levels of fibre which reduce the value of DDGS in aquaculture feeds. In this study, sieving was used to fractionate wheat DDGS. Wheat DDGS was ground using a hammer mill with a 3 mm screen and the ground material fractionated using six sieves (No. 20, 30, 40, 50, 60, 80 sieves and pan) creating seven fractions. Nine diets were made, diet 1 (reference diet), diet 2 contained 300 g/kg original unsieved wheat DDGS and 700 g/kg reference diet, and the remaining seven diets consisted of 300 g/kg of the sieved fractions and 700 g/kg reference diet. Results showed sieving wheat DDGS increased CP from 371.6 g/kg in the original material to 432.4 g/kg in the pan fraction (P<0.05). Furthermore, sieving decreased neutral detergent fibre (NDF) from 271.2 to 215.5 g/kg and acid detergent fibre (ADF) from 98.9 to 76.7 g/kg (P<0.05). Apparent digestibility coefficients (ADC) for energy and dry matter (DM) were increased in fractions 80 and pan, however, ADC for CP was not significantly affected by sieving (P<0.05). The increase in nutrient concentration coupled with increased ADC resulted in significant increases in the level of digestible DM, energy and CP compared to the start material. Overall sieving provides a low-cost method for improving the nutritional value of wheat DDGS in rainbow trout.