Date of this Version
Fifty-three index select and control line barrows were randomly assigned to three feeding levels at 83 d of age. They were slaughtered at approximately 188 d of age to determine the effects of index selection (for increased average daily gain and decreased backfat) and level of feed intake on energy utilization. During the trial, the feed intake levels were twice daily to appetite (AP), once daily feeding of 91% of appetite (AP91) or once daily feeding of 82% of appetite (AP82) intake. The metabolizable energy intake required per kilogram of edible lean deposited (Mcal/kg) was reduced (P<.05) by restricting intake and was lower (P<.01) for index than for control barrows [index: 25.6 (AP), 23.3 (AP91) and 25.3 (AP82) vs control: 31.1 (AP), 27.5 (AP91) and 28.1 (AP82)]. However, intake restriction and index selection increased (P<.05) the energy lost per unit of retained energy (index: 1.33, 1.45 and 1.53 vs control: 1.24, 1.29 and 1.34). The index line had a higher (P<.05) maintenance requirement than the control line when expressed unit of weight (kg.75)-1 x day -1, but the difference was less when expressed unit of lean (kg.83)-1x day-1. The energy cost of protein deposition varied from 9.02 to 11.25 kcal/g, while the energy cost of fat deposition ranged from 12.73 to 12.86 kcal/g. Variation among animals in metabolizable energy intake was explained by variation in lean mass maintained and the quantity of protein and fat deposited.