There are three measures of feed efficiency in common use today. These measures or their component traits have been shown to be heritable, so selection for improvement is possible but anticipated to be slow, requiring a decade or more to move the population a meaningful distance.
Feed Efficiency or Feed Conversion Ratio: Many cow-calf producers and, certainly cattle feeders, are familiar with the term feed efficiency (FE; live weight gain per unit of feed consumed) or its reciprocal, feed conversion ratio (FCR; F:G or pounds of feed per pound of live gain). Both of these measures are most commonly associated with animals during the growing or finishing phases. Both measures are suitable for managerial use during feeding but are poor selection tools.
Residual Feed Intake: Recently, residual feed intake has been reintroduced as an efficiency measure for beef production. It is computed as the difference between actual average daily feed intake (AFI) and the predicted daily dry-matter intake based on the animal’s gain and maintenance requirements for its body weight. The actual calculation results in an RFI value that is not correlated with phenotypic ADG and body weight, which is an advantage over FCR or FE. RFI can and does identify efficient animals that also have slow growth and low feed intake making these candidates undesirable for selection and use in the commercial beef industry. Some research suggests that selection for RFI produces slightly larger and leaner cows over time and cows that have older ages at first calving. In general, selection for favorable (negative) RFI results in animals with equivalent performance, but achieves that output with less feed consumed.
Residual Average Daily Gain: A concept closely related to RFI is residual average daily gain (RADG) which was proposed at the same time as RFI as a potential tool for selection for improved feed efficiency. This term is defined as the difference between actual weight gain and the gain predicted based on dry matter intake, maintenance of body weight and fat cover. In the calculation, differences in ADG are controlled/adjusted for differences in AFI and body weight. Like RFI, RADG, is a transformation of the data and can be computed based on either the live measurements alone (phenotypic) or by information from both the individual and relative data (genetic). While RADG is indicative of differences in efficiency of feed utilization for growing animals, it may have limited utility for prediction of differences in maintenance efficiency of cows.
These measures of efficiency are most commonly discussed when considering data that measure individual intake of growing animals in a feedlot setting. Cow/calf producers that retain an interest or ownership of calves through harvest may be considering them as options to improve profitability of the finishing phase of production. Since growth is not a desired output of the cow, other measures of cow efficiency are needed that account for reproduction, maintenance and milk production.
For more detailed information on these measures and their use in selection, read “Improving efficiency starts with understanding the measures.”
Answer from Dr. Bob Weaber, Extension cow-calf specialist, Kansas State University