GROWTH AND CARCASS COMPOSITION OF PIGS FED DIETS THAT CONTAINED RAPESEED OIL, SOYBEAN OIL OR TALLOW DURING THE GROWING PERIOD

Sixteen barrows and 16 gilts in experiment 1 were fed diets that contained 10% by weight cornstarch, tallow, soybean oil (SBO) or rapeseed oil (RSO) and 20% protein (N × 6.25) from 8 to 23 kg and 18% protein from 23 to 45 kg liveweight. In experiment 2, 32 barrows received the same diets except that the SBO treatment was replaced by 10% cornstarch diets containing 19% protein from 8 to 23 kg and 16% protein from 23 to 45 kg. All pigs were fed a commercial diet that contained 15% protein from 45 to 90 kg liveweight. Source or substitution of fat for cornstarch had no significant effect on weight gain during the growing (8–45 kg) or subsequent finishing (45–90 kg) periods, on the carcass measurements obtained after slaughter at 90 kg liveweight, on average daily feed intake, efficiency of feed utilization or of energy utilization; however, the number of degrees of freedom (df = 7) were small for the latter three parameters. Level and source of dietary fat did affect the fatty acid composition, as determined by gas–liquid chromatography, of the backfat at 45 and 90 kg. The ratios of unsaturated to saturated fatty acids were significantly higher at 45 kg in the fat from pigs fed the tallow or RSO diets than those fed the cornstarch diets. A similar trend remained at 90 kg. The backfat of pigs fed the RSO diet contained 7.6 and 7.8% of erucic and eicosenoic acids, respectively, at 45 kg and still 2.3 to 3.7% of the total at 90 kg, even though the diet fed between 45 and 90 kg liveweight did not contain these fatty acids.