Effect of Plane of Nutrition, Sex and Bodyweight on the Chemical Composition of Yorkshire Pigs

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Abstract
An experiment was carried out involving the full- vs. limited-feeding of 9 pairs of gilts and 6 of barrows from a population of closely related Yorkshire pigs from approximately 45 kg. live weight up to each of three predetermined slaughter weight groups (79, 90 and 102 kg.). The objective was to determine the effects of level of feed intake, sex and weight on the chemical composition of the empty body, edible carcass and inedible parts (offal) and the fatty acid composition of the mid-back fat. As the slaughter weight increased, the percentages of empty body, carcass and offal protein and water decreased significantly, while the percentage of extractable fat increased significantly. These changes were most noticeable between the lightest (79 kg.) vs. the two heavy groups (90 and 102 kg.), but the two heavy groups had similar chemical composition. In absolute quantities, the protein, fat, water and ash increased as the slaughter weight increased. Since the chemical composition of the offal followed the same trends as observed for the carcass or the empty body and were fairly close in the three categories, it would appear that a reasonably high impression of the chemical composition of either the empty body or the carcass could be gained by analyzing the inedible parts (head, empty gastrointestinal tract and all other internal organs) and saving the edible carcass. There were no significant weight group differences in the fatty acid composition of the back fat, but the lightest pigs had slightly higher proportions of the unsaturated fatty acids and less of the saturated ones than the heavy groups. The restricted-fed pigs in all cases had higher percentages of protein, ash and water, and lower fat than the full-fed pigs; these differences being significant in most of the comparisons, except for the ash content that showed no significant differences in the carcass, offal or empty body. The absolute quantities of the protein, fat, ash and water for full- vs. limited-fed pigs followed the same trends as the percentages above. Feed restriction had the effect of increasing significantly the percentages of most of the unsaturated fatty acids and decreasing the percentages of the saturated fatty acids.