RESIDUAL FEED INTAKE IN CATTLE: PHYSIOLOGICAL BASIS. A Review

Residual feed intake (RFI) is an estimate of feed efficiency independent of the level of production. Briefly, RFI is estimated as the difference between the observed and the expected intake for a given live weight gain and metabolic body weight. Therefore, cattle with lower RFI are considered to be more efficient. No single biological mechanism explain the variability in RFI. Research has shown that low RFI cattle generate less methane per unit of live weight gain, but it is not clear if they yield less methane per unit of dry matter intake. Differences in digestion and rumen function have been reported. According to some evidence, low RFI cattle would have lower maintenance requirements, but results are inconclusive. Some evidence suggests that they have a lower protein turnover. Activity and feeding behavior differs in cattle contrasting in RFI and more efficient cattle would be less active and would show lower daily number of feeding events. Gain composition seems also related to RFI but it does not appear to be the main factor. Visceral weight, mitochondrial function and hormones have also been studied, with inconclusive results. Residual feed intake relies on multiple physiological traits and further elucidation of implications will be important for the implementation of selection programs in cattle.