BODY PROPORTIONS AND CARCASS COMPOSITION OF PIGS WITH KNOWN GENOTYPES FOR STRESS SUSCEPTIBILITY FASTED FOR DIFFERENT PERIODS OF TIME PRIOR TO SLAUGHTER

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Abstract
A total of 233 pigs from a halothane positive line (genotype nn), from a halothane-negative line (genotype NN) and their cross (genotype Nn) were allocated to three treatments when their liveweight approximated 95 kg. Treatment 1 consisted of immediate slaughter following removal of the pigs from their pens, treatment 2 involved a period of 24 h of feed restriction prior to slaughter and treatment 3 a period of 48 h of feed restriction prior to slaughter. All carcasses were weighed on the slaughter floor and cooled at 1 °C for 24 h prior to dissection of the side into fat, lean and bone. Relative to liveweight, nn pigs had a higher proportion of carcass (41 g kg−1, P < 0.001) and a lower proportion of body organs (8 g kg−1, P < 0.001), body fat depots (7 g kg−1, P < 0.001), alimentary tract (14 g kg−1, P < 0.001) and gutfill (12 g kg−1, P < 0.001) than NN pigs. Nn pigs had values that were generally intermediate to nn and NN pigs. The proportion of carcass (22 g kg−1), body organs (5 g kg−1), alimentary tract (6 g kg−1) and gutfill (21 g kg−1) were reduced (P < 0.05) as fasting increased from 0 to 48 h relative to market weight. Linear fat thickness measurements made on the midline of the warm carcass were similar for nn and NN pigs except for the maximum loin (32.2 vs 28.6 mm for nn vs. NN). However, nn pigs had a lower proportion (P < 0.05) of fat (35 g kg−1), bone (13 g kg−1) and skin (11 g kg−1), and a higher proportion of lean (60 g kg−1) in their carcasses than those from NN pigs. Carcasses from Nn pigs had less skin (4 g kg−1) and bone (7 g kg−1), but more lean (11 g kg−1) and similar fat content to those from NN pigs. It was concluded that fasting for up to 48 h prior to slaughter had a similar effect on the three genotypes, but there were large differences among genotypes in body components and carcass composition. Key words: Stress susceptibility, fasting, carcass, organs, gutfill, composition, pigs