Published online by Cambridge University Press: 27 February 2018
The rôle of voluntary food intake, measured as daily food consumption on ad libitum feeding from 30 to 90 kg live weight, in future selection strategy is reviewed. Intake shows a heritability of 0.3, and genetic correlations of 0.6 with growth rate and –0.4 with leanness. Low genetic correlations between test station and commercial farm performance are reported for growth rate (0.27) and backfat (0.41) which arise either from genotype × feeding level interactions, or from individual feeding at stations. Selection for rate of lean growth appears to lead to a primary increase in rate of protein deposition, whereas selection for efficiency of lean growth appears to lead to a reduction in rate of fat deposition via a decline in intake. Continued reduction in intake may limit further improvement in lean growth rate and sow productivity. As optimum fatness is approached, the selection emphasis is expected to swing towards rate of lean growth to reduce total food used for maintenance. To determine the optimum selection regime, a knowledge is required of the genetic relationship between intake and lean growth rate. Meanwhile, the optimum selection regime may involve ad libitum group feeding with electronic recording of individual food intake. In the long term, exogenous or endogenous growth promoters could remove the need for selection against backfat, and necessitate a radical genetic increase in intake.