The effect of extrusion on the nutritive value of rapeseed meal for growing and finishing pigs

Two experiments were conducted to determine the nutritive value of extruded '00' rapeseed meal as a protein supplement for pigs of 37 to 95 kg live weight. The effects of extrusion on the apparent digestibility coefficients of the organic matter, crude protein, energy, neutral detergent fibre and the digestible energy fractions of rapeseed meal, when included in the diet at 200 or 400 g/kg, were determined in Experiment 1. The diets were (DO) control diet (barley, wheat, soyabean meal, tallow, molasses and mineral and vitamins), (D1) control diet (800 g/kg) plus rapeseed meal (200 g/kg), (D2) control diet (800 g/kg) plus extruded rapeseed meal (200 g/kg), (D3) control diet (600 g/kg) plus rapeseed meal (400 g/kg) and (D4) control diet (600 g/kg) plus extruded rapeseed meal (400 g/kg). In Experiment 2, performance was evaluated using individually fed pigs (n = 72) offered one of six diets ad libitum. The diets were control (TO) (532 g wheat, 189 g soyabean meal, 150 g peas, 40.0 g tallow and 40 g molasses per kg) and diets containing 100 (T1), 200 (T2) or 300 (T3) g of rapeseed meal/kg or 200 (T4) or 300 (T5) g of extruded rapeseed meal/kg. The extruded rapeseed meal had been extruded at 120 degreesC for 30 s. All diets were formulated, using standard values for ingredients, to have the same concentration of digestible energy (13.8 MJ/kg) and lysine (11 g/kg). In Experiment 1, extrusion resulted in a significant increase in the apparent digestibility of organic matter (0.797 v. 0.729, s.e. 0.0185; P < 0.05) and energy (0.755 v. 0.678, s.e. 0.023; P < 0.05) in the rapeseed meal and increased the digestible energy content (13.9 v. 13.1 MJ/kg dry matter, s.e. 0.41; P = 0.09). In Experiment 2, there was a linear increase in feed conversion ratio (FCR) (P = 0.09) and a linear decrease in growth rate (P < 0.1) during the fall experimental period as the level of raw rapeseed meal increased in the diet. Extrusion of the rapeseed meal had no significant effect on feed intake, growth rate or FCR during the grower (first 5 weeks), finisher (week 6 to slaughter) or the combined grower-finisher period. Gains (kg/day) of 0.959, 0.946, 0.872, 0.919, 0.932 and 0.914 (s.e. 0.0227) (P < 0.05) and FCR of 2.29, 2.38, 2.43, 2.40, 2.37 and 2.42 (s.e. 0.0369) (P < 0.05) were recorded for the T0 to T5, respectively, There was a linear decrease in pig performance as the level of rapeseed meal increased in the diet while the inclusion of extruded rapeseed meal had no beneficial effect on pig performance.