The effect of level and source of protein, fibre and fat in the diet on the energy value of compounded pig feeds

The digestibility of protein, fibre and fat sources, when added at various levels to a constant basal diet, was determined in growing pigs. Digestible energy (DE) contents of the foods were estimated by regression of DE intake against level of addition of test food. The DE values (MJ/kg DM) obtained were: fish meal, 19.1; soya bean meal, 17.1; oatfeed, 9.4; extracted rice bran, 11.3; sugar beet pulp, 12.7; tallow, 38.8; palm acid oil, 37.5; soya oil, 40.8. The DE of barley was 14.7 MJ/kg DM and the DE of wheat was calculated to be 15.2 MJ/kg DM. The DE values of barley and fish meal with pregnant sows were 14.7 and 19.2 MJ/kg DM, respectively. Digestibility of fibre components was very variable between pigs and sources of fibre, sugar beet pulp having the highest digestibility values. Digestibility values for the fat sources were high at 0.963, 0.917 and 0.981 for tallow, palm acid oil and soya oil, respectively. Prediction of dietary DE from fibre content was best achieved by use of neutral detergent fibre (DE = 17.37 - 0.016 NDF; R² = 0.90). Application of predictive equations derived from diets with one fibre source to another source gave rise to substantial error. Prediction of dietary DE from oil content was more successful, and predictive equations were similar for all fat sources.