Production levels in livestock (cattle, pigs and poultry) have been increased considerably, with a correlated increase in gross feed efficiency. However, mature body weight has also increased, leading to higher maintenance costs. Thus, net feed efficiency has been little improved. Breeding for lower body weight has not been successful, but there are possibilities for reduction of feed consumption independent of production and body weight (residual feed consumption). It is as yet uncertain to what extent animal stress susceptibility will be affected by changes in residual feed consumption.