Comparative performance and body composition of control and selection line large white pigs 2. Feeding to appetite for a fixed time

Food intake was individually measured for Large White control (C) and 10th generation index-selected (S) pigs fed twice daily to appetite on a fixed time trial. Thirty-nine C and 38 S boars were slaughtered, their carcasses dissected and whole empty bodies minced and chemically analysed after an 84-day trial starting at 28·6 ± 0·30 kg live weight. S boars ate proportionately 0·08 less than C boars in the first 42 days of the trial (79 v. 86 kg, P < 0·01), but S and C boars ate similar amounts (114 v. 117 kg, NS) in the last 42 days. S boars grew 0-04 faster than C boars (918 v. 886 g per day, NS), and had 0·09 better food conversion efficiency (0·404 v. 0·369 gain per kg food, P < 0·001). S boars contained more water than C boars (53·5 v. 48·9 kg, P < 0·001), more protein (15-4 v. 14-2 kg, P < 0·01), less lipid (20·8 v. 25·1 kg, P < 0·001), less gross energy (1 199 v. 1 357 MJ, P < 0·01) but a similar amount of ash. S carcasses had 3 kg more lean (36·5 v. 33·5 kg, P < 0·001) and more bone than C carcasses (7·14 v. 6·71 kg, P < 0·05), but contained 3 kg less total fat (19·6 v. 22·6 kg, P < 0·01). The lean tissue growth rate of S boars was 327 g per day which was 31 g per day faster than for C boars (P < 0·001). Appetite reduction in S boars enhanced fatness differences between the lines.