Balancing Bull Selection with Feed Intake
Now that the beef industry has increased access to individual feed intake records from test station sources, we move to the task of how to optimally incorporate this new information into genetic evaluation and improvement programs. It is important to realize that even though various measures of efficiency have been proposed and studied, the core piece of new information is individual feed intake. We now recognize that actual feed intake measurement is essential to genetic improvement.
The feed we purchase to finish cattle, along with forages and supplemental feeds for stockers and cows, represent the largest variable cost of producing beef and is clearly a cost-side economically relevant trait.
A central question is, “How is the best way to use this information to make selection decisions?”
Of the several traits that have been more intensively discussed recently, we have to keep in mind that no one EPD tool will be optimal. Foremost, genetic improvement based on single-trait selection is not sustainable, nor advisable. The real question is how we balance the EPD tools we have available to make better decisions, recognizing their relative economic importance across multiple production and marketing systems
In developing profitable selection programs, we must consider potential genetic antagonisms that contribute to making progress in one trait, but at the same time, losing ground in another important trait.
With feed intake, we make decisions that recognize its importance, but at the same time, recognizing that cattle that eat the least and cost the least to feed may not always be the most profitable.
The most widely discussed feed efficiency trait that combines feed intake with other traits is residual feed intake (RFI), which adjusts intake for differences in body weight (BW) and level of production. RFI is the difference between a bull’s actual intake and its expected intake based on body weight and ADG. Those bulls that eat less than expected will have a negative RFI and be more efficient compared to those with a positive RFI.
A growth trait that can be forced to be independent of intake is often referred to as residual gain (RDG). RFI and RDG are intake and growth rate traits, respectively, and these examples emphasize the point against single trait selection.
Residual feed intake, where lower or more negative numbers are considered desirable, measures the amount of feed a bull eats above or below what we’d expect given his growth rate and body size.
Residual gain, on the other hand, measures the difference between growth rate, or average daily gain on test, of a bull and what we would expect the bull to gain given how much he eats and his size, and more positive or higher RDG values may be more desirable.
In developing more comprehensive terminal and maternal indexes, the objective is to identify those bulls that are more profitable in their production system, mainly that are high producers, but also that require less input costs.
We can and should continue building selection indexes that incorporate a balance of EPDs that account for a wider range of traits that impact both the costs and revenues of producing beef. These are restricted examples of selection indexes, just like total maternal EPD and breed-wide indexes that focus on certain marketing systems. Always remember, bulls will rank differently regardless of which index is used.
Genetically speaking, we would use both the relative economic importance and the associations among several traits, including intake, to provide a tool that is relevant to the efficiency of the total system beyond those measured on tested bulls. Retained ownership systems, for example, easily illustrate the importance of efficiency as a tool to increase profitability. But what about the replacement sisters of those feedlot calves? Will they breed as heifers and go on to have long productive herd life? And how big of a cow type will they become? Another example would be a weaned calf market system where heifers are retained. Do we just want bulls in this system that eat less and grow fast on test? How will their retained daughters perform as cows on range?
Research shows we can answer all of these questions, and we start by recognizing the importance of feed intake. Not just for bulls, but also cows, steers and replacement and cull heifers. The residual measures of intake and growth that we have known about since the 1960s are useful steps toward more balanced bull selection now that this industry is getting serious about measuring feed intake.
