Rising feed prices and shrinking margins have generated significant discussion on animal efficiency. We have all seen those cows that we call “easy doers” but did not give them much thought until recently.

These are typically animals that seem to be in better flesh than their contemporaries under the same circumstances.

These animals can be seen in all species. For some reason, they just seem to be able to do more with less than other cows in the herd.

Residual feed intake, or RFI, is a strategy science has generated that is designed to not only help us identify the more efficient animals but also be able to compare individuals for varying degrees of efficiency.

The system was developed initially to determine feedlot performance efficiency but has recently been utilized to determine energy use for other physiological demands.

RFI has become a prominent trait of interest for assessment of feed efficiency. RFIs are defined as the difference between predicted average daily intake adjusted for performance and the animal’s actual average daily intake.

By using a statistical method of regression, the average daily intake of an animal can be estimated (or predicted) based on a level of performance.

In the case of beef cattle, the level of performance is the amount of feed it takes for an animal to increase in weight.

The resulting estimation is then compared to an animal’s actual individual average daily intake. The difference from the estimated daily intake and what the animal actually consumes is the RFI.

For example, we have a pen of 30 steers on a finishing ration in a feedlot. The pen average daily intake for steers that weigh 1,300 pounds is 30 pounds of feed per day.

Steers A and B both weigh 1,300 pounds. Steer A requires 36 pounds of feed per day, and steer B requires 23 pounds of feed per day to reach this weight of 1,300 pounds.

Steer A has an RFI of +6 and steer B has an RFI of -7. As a result, steer B would be more efficient since he requires less feed to gain the same amount of weight as steer A. These steers are fed the same diet and are gaining under the same environmental conditions.

In order to calculate RFI values, individual animal intakes and weights need to be collected. Animals would have to be housed in a facility capable of measuring an animal’s individual feed intake.

Colorado State University’s Feed Intake Unit (FIU) is equipped with a system which allows for individual feed intakes to be measured on animals in a feedlot setting.

Since it is expected that intakes will vary from day to day, and animals will be gaining weight, animals will have to be housed for a period of time in order to measure a reliable average daily intake and rate of gain.

Current recommendations for measuring feed intakes are a 21-day adaptation period followed by a 70-day testing period. The adaptation period allows animals in the FIU to adjust to the feedbunks and the test ration.

Following this adaptation period, the cattle enter into a test period when intakes and weights are measured. This testing period needs to be of adequate length to capture the rate of gain and to calculate reliable average daily intakes for animals on test.

Currently, testing length is recommended to be 70 days. During this 70-day testing period, weights are collected on the cattle every two weeks. The system collects the amount of feed consumed by each individual animal on test.

The individual intake is measured by the animal consuming feed from a bunk that weighs the feed when the animal enters the bunk and when he exits the bunk. Only one animal can access the bunk at a time.

Typically, each pen has four bunks, and each pen has around 30 animals. At the end of the 70-day test, the individual animal’s consumption is averaged resulting in an average daily intake for that animal.

In addition, average daily gains are calculated for each animal. The resulting average daily intakes and average daily gains are then used to calculate RFIs.

There are advantages to RFI compared to other, more traditional tools for feed efficiency, such as feed-to-gain ratios.

Research has shown that RFIs are heritable and may be used as a selection criterion. The selection for lower RFI has resulted in cattle with lower feed consumption without sacrificing growth performance.

This is in contrast to feed-to-gain ratios. Ratios are difficult to improve with direct selection. In addition, ratios are problematic as a selection tool in that animals with similar feed-to-gain ratios may have very different intakes or gain.

RFIs are not perfect; there are disadvantages to RFIs that should also be considered. One disadvantage is that RFIs are calculated based on the animals on test.

In addition, slower-growing animals eating small amounts of feed would result in a negative and more desirable RFI.

The resulting negative RFI would indicate an animal that is more efficient, when in fact he is smaller and just not eating as much.

There is no doubt that other methods will be established, as the need to identify more efficient animals is going to continue. 

Kraig Peel is also the director of the Western Center for Integrated Resource Management Systems.

Miranda Culberson is a graduate student in breeding and genetics at Colorado State University.