Genetic variation and covariation in voluntary feed intake in pig selection programmes

Literature on the genetic variation in Voluntary Feed Intake (VFI) and traits related to VFI under ad lib. and restricted feeding has been reviewed. Also differences between breeds and selection lines are reviewed and discussed. Heritability estimates of VFI show average values of 0.12–0.59, with larger variation on real ad lib. feeding compared to “to appetite” feeding twice a day. It is also concluded that the genetic correlation between feed intake and gain is higher under ad lib. feeding than under restricted feeding, and that genetic correlation between daily gain and feed/gain decreases from about −0.9 under restricted feeding to about −0.6 under ad lib. feeding. Results from a Norwegian selection experiment indicate that there is no correlated response in daily feed intake (feeding “to appetite”) when selecting on backfat and daily gain, while other selection experiments, where feed conversion ratio has been the major component of the selection index, show reduced appetite. The present paper discusses the danger of reduced appetite in selection programmes that maximize short-term economic gain, and the importance of selection objectives and feeding regime on the genetic correlations between VFI and other production traits. A comparison is also made between population parameters of Norwegian and Danish Landrace pigs.