The influence of rapeseed oil on digestibility, energy metabolism and tissue fatty acid composition in pigs

The influence of rapeseed oil on digestibility, energy metabolism and tissue composition in growing pigs was determined. Rapeseed oil (0, 4, 8 and 16%) was added to a soyabean meal and barley basal diet. Essential amino acids relative to net energy (NE) were kept constant by adjusting with crystalline amino acids. Rapeseed oil has a high content of the unsaturated fatty acids 18:1n-9, 18:2n-6 and 18:3n-3, and is rich in natural tocopherols, which act as antioxidants. The apparent protein digestibility was enhanced with increasing levels of rapeseed oil. Improving the ratio of essential to non-essential amino acids decreased nitrogen execretion in faeces and urine by 21% and 26%, respectively. The amount of digestible fat increased from 29 to 218 g day(-1) from the control diet to the diet with 16% rapeseed oil, resulting in a fat retention of 195 to 213 g day(-1). This demonstrates the ability of pig for de novo synthesis of fatty acids. The digestibility of the rapeseed oil was high (92.7), and the metabolizable energy (ME) content of rapeseed oil was 38.28 MJ ME kg(-1). The net energy value of the rapeseed oil corresponded to 3.66 kg air dry barley. Higher intakes of unsaturated fatty acids in rapeseed oil were reflected in the body tissue composition of both depot fat and intramuscular fat of the pigs. The fatty acid composition of these tissues became more unsaturated with respect to 18:2n-6 and 18:3n-3 as well as 20:5n-3 and 22:5n-3. Arachidonic acid (20:4n-6) increased slightly in leaf fat but tended to decrease in M. longissimus dorsi and M. biceps femoris, where docosahexaenoic acid (22:6n-3) in leaf fat was unaffected by dietary rapeseed oil level. In the analysed muscles 22:6n-3 tended to decrease with increasing dietary rapeseed oil level.