Possible reasons for differences in residual feed intake: An overview

Abstract

Selection for residual feed intake (RFI) as a trait to improveproduction efficiency was proposed as early as 1963. A low RFI valueindicates a more efficient animal and heritability estimates of between0.28 and 0.58 have been reported for RFI in the literature. It is alsoreported that a 13.38 g/d reduction in methane emission was associatedwith a 1 kg/d reduction in the Estimated Breeding Value (EBV) for RFI,with low-RFI steers emitting 25% less methane daily. The difference inmethane production in high and low RFI animals cannot be explained bythe difference in feed intake alone. Possible reasons could be digestionof feed, protein turnover and overall tissue metabolism (mitochondrialfunction, body composition, Insulin Growth Factor-I (IGF-I) and cortisollevels), activity, thermoregulation and growth. Low-RFI animals tend todigest feed better than high-RFI animals, and as intake increases thereis a tendency for digestion to decrease. The correlation between RFI anddry matter (DM) digestibility has been determined to be r = -0.33. Apositive correlation exists between metabolisable energy for maintenance(ME) and RFI, as well as between ME and protein turnover. Thus proteinsecretion in low-RFI animals are the same as high-RFI animals, but thebreakdown of protein in low-RFI animals is less. Clear differences canbe observed in heat production, with low-RFI animals producing up to21% less heat than high-RFI animals. Selection for low-RFI animals maythus reduce the carbon footprint of beef cattle.