RFI is estimated by the difference between actual and predicted feed intake for an animal. The predicted feed intake
is the amount of feed the animal is expected to consume on the basis of its maintenance and production. Variation in RFI
may reflect differences in the efficiency with which animals digest and utilize energy for maintenance and production. The objective of this study was to estimate genetic parameters for and genetic relationships between measures of RFI and growth traits, and to examine the genetic trends of these traits in Duroc pigs over seven generations of selection based on average daily gain (ADG), loin eye area (LEA), backfat thickness (BF), and intramuscular fat (IMF). Results of this study indicate that residual feed intake was moderately heritable, and should respond to selection.
Genetic correlations indicate that it should be possible to select for reduced residual feed intake without adversely
affecting average daily gain. Daily feed intake and backfat would also decrease, and eye muscle area would increase. The
amount of change in backfat or eye muscle area would depend on which measure of residual feed intake one uses.

For more information the full article can be found at http://www.journals.elsevierhealth.com/periodicals/livsci