Comparative performance and body composition of control and selection line large white pigs 1. On a generous fixed feeding scale for a fixed time

Growth performance and body composition differences between Large White control (C) and 10th generation index-selected (S) pigs were evaluated on a fixed food, fixed time trial. This avoided the complicated interpretation associated with interacting variations in food intake, days on test and body composition. Thirty-nine C and 40 S boars were slaughtered, their carcasses dissected and whole empty bodies minced and chemically analysed after an 84-day trial starting at 26·6 ± 0·27 kg live weight. S boars were older at the start of test (95·2 v. 89·0 days, P < 0·001), were heavier at the end of test (96·2 v. 93·8 kg, P < 001) and converted food more efficiently (0·392 v. 0·378 kg gain per kg food, P < 0·01) than C boars. Bodies of S boars contained more water (48·3 v. 45·9 kg, P < 0·001), less lipid (17·4 v. 18·8 kg, P < 0·001) less gross energy (1 004 v. 1 045 MJ, P < 0·05), but similar amounts of protein (13·8 v. 13·4 kg, NS) compared with C boars. S carcasses contained more lean (34·1 v. 31·8 kg, P < 0·001), less subcutaneous fat (12·5 v. 13·7 kg, P < 0·001), and had lower P2 backfat depths (15·8 v. 18·3 mm, P < 0·001) than C carcasses. Although carcass leanness had been increased, 10 generations of index selection had also reduced the overall energetic efficiency of the selection line, apparently by increasing non-productive heat loss.