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Selecting for Feed Efficiency in Beef Cattle

By Randie Culbertson, Ph.D.     |   

Cattle producers have become increasingly aware of the need to improve feed utilization in beef cattle.

It is reported that feed costs are the largest expense to cattle producers accounting for 50 to 70% of total production costs. When corn prices approached $7 per bushel, the price of feed accounted for 80% of production costs for many feedlot operations. Decreasing feed costs without sacrificing animal performance would have a large economic impact on beef operations. The question then remains, how?

In the context of selecting cattle who are more feed efficient there is a large debate over what is the best phenotype, how to incorporate it into a breeding program or genetic evaluation, and what impacts selection would have on other performance traits. The two phenotypes at the center of this debate are feed intake (FI) and residual feed intake (RFI).Residual Feed Intake:

Residual feed intake is defined as the difference between what the animal’s actual measured feed intake was compared to his expected intake given his level of performance. A negative RFI represents an animal who ate less than what he was expected to eat, and a result would be considered to be a more feed efficient animal. 

Some of the advantages to RFI are that it is a measure of feed efficiency since it accounts for the animal’s level of performance and has no phenotypic correlation to traits included in its calculation (i.e. average daily gain). Therefore, selecting for lower RFI would select for an animal with lower feed intake for a certain level of performance. Although RFI is not phenotypically correlated to performance traits, there is genetic correlation. Selection for lower RFI would impact other performance traits such as weaning and yearling weight.

There are also significant disadvantages to RFI. First, RFI has a tendency to favor slower growing animals which may not be the most profitable animal. RFI is the result from a multiple regression model (requiring statistical software to compute) where the variables included in the model can vary depending on the testing facility and could affect the ranking of animals within a contemporary group. In addition, the actual RFI value can only be compared to other animals included in its calculation and cannot be directly compared to RFI values from different tests or locations.

Feed Intake:

Feed intake is defined as the measure of actual feed consumed by an animal and as a result, can be compared across different tests. Conceptually, FI is easy to understand and doesn’t require any additional calculations. An increase in FI simply means that the animal consumed more feed and vice versa. However, FI is not a measure of efficiency since it gives no indication of an animal’s performance but is significant in the calculation of feed efficiency traits such as RFI. FI intake is influenced by many physiological factors and is correlated to performance traits such as average daily gain. As a result, as an animal’s body size increases, so does FI.

So why the debate?

The question of incorporating FI or RFI into a breeding objective is an ongoing debate. The reduction of FI should not be the sole objective of a breeding program, instead, selection for improved feed efficiency could be achieved by simultaneous selection for all traits that influence production profitability rather than individual trait selection. This can be accomplished through selection based on an economic index with appropriate weighting for performance traits as positive and feed intake as negative. As a result, feed efficiency would not have to be explicitly calculated and genetic selection for improved production efficiency could be achieved through simultaneous selection for all traits that influence profitability rather than individual trait selection.

 

 Example of Residual Feed Intake (RFI) for two steers from the same feeding trial.
   Steer A   Steer B
 RFI   -4.90   -3.09
 Average Daily Gain   2.48 lbs/day  4.35 lbs/ day
 Average Feed Intake*   22.33 lbs/day  29.20 lbs/day
 Final Test Weight  915 lbs  1300 lbs
     

 Steer A is considered the more feed efficient animal based on his RFI (lower number is better) but he is also much smaller than steer B with an average daily gain that is about half. Although steer A might save you money with lower feed costs, he might not be as profitable given his small size. RFI doesn’t take into account other production traits that may affect profitability. Using an index that includes FI, average daily gain, and carcass traits is the best way to select for profitable genetics.

* Feed intake reported on a dry matter basis.

Conclusion: To maximize profit, use FI in an index with other economically relevant production traits (i.e. average daily gain and carcass traits) to advance your genetic prowess in the commercial industry. At the end of the day, your breeding objective shouldn’t be just the reduction of feed but the increased profitability of your customers’ cattle

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