Apparent digestibility of high-fat rapeseed press cake in growing pigs and effects on feed intake, growth and weight of thyroid and liver

Rapeseed from a winter variety of Brassica napus was pressed through a screw press. The press cake (321 g crude protein, 180 g crude fat, 102 g crude fibre, glucosinolates at 18 mmol kg−1 DM (dry matter)) was tested either untreated or soaked (11 water kg−1 rapeseed press cake) and dried at 60°C. Press cake contained 28% more glucosinolates than the corresponding seed. Moist heat treatment caused a reduction of glucosinolate content to 0.3 mmol kg−1 press cake DM. Glucosinolate degradation products were not detectable (less than 0.1 mmol kg−1 DM). In a digestibility experiment consisting of two periods in a 2 × 4 crossover design four pigs received barley or diets with rapeseed press cake 500 g kg−1 as a replacement for barley. The digestibility of all measured parameters except fat was lower in the rapeseed press cake than in barley (%): crude protein 68.5 vs. 77.8, crude fat 78.4 vs. 46.4, crude fibre 14.7 vs. 42.2, N-free extract 83.8 vs. 92.4, organic matter 70.0 vs. 84.7. The differences were all significant (P < 0.05). A metabolizable energy (ME) of rapeseed press cake of 14.1 MJ kg−1 DM was calculated, and this value was similar to that calculated for barley (14.6 MJ ME kg−1 DM). In a further 16 week experiment with four groups of ten pigs, diets with 0, 50 g, 100 g or 150 g rapeseed press cake per kilogram were tested. In a final experiment the highest rapeseed press cake level (150 g kg−1 diet) was also treated with moisture and heat. There was no significant effect of dietary level or treatment of rapeseed press cake on performance criteria. There was a trend (P < 0.1) for daily weight gain to decrease with increasing press cake level. The dietary rapeseed press cake level caused a significant increase in thyroid and liver weights. In the group with untreated press cake at 150 g kg−1 diet the thyroid weight was trebled and the liver weight increased by 20%. Treatment significantly lowered the weight of organs. The weight of the thyroid, as well as of the liver, was significantly higher in this group with moist-heat treated rapeseed press cake at 150 g kg−1 than in animals of the glucosinolate-free control group.