This may seem elementary, but it is important to remember that all consumed are to be partitioned to support important metabolic functions.

Assuming two animals with identical nutrient requirements eat the exact same amount of feed, why does one animal gain more weight than another? Do animals with greater efficiency utilize more of their energy for metabolism or growth and subsequently less for other processes, such as reproduction?

There is evidence that selection for efficiency alone can exert some detrimental effects on production in both sheep and cattle. Factors such as age of puberty could be negatively associated with feed efficiency.

Scientific reports indicate there is a correlation between age at puberty and duration of post partum interval in cattle. If age of puberty in cattle is increased through selection, there is a possibility of affecting the cows’ ability to rebreed in a timely manner each year. 

Data in this area are inconclusive and should be sorted out before selection decisions are based on perceived economic advantages of selecting for feed efficiency alone.

How big of an economic value is associated with increased feed efficiency? One of the misunderstandings of RFI and efficiency is that these values do not necessarily translate to profitability.

A recent evaluation of Grow Safe data from bull tests conducted at the University of Wyoming demonstrated that selection for RFI, or efficiency, does not translate to performance or profitability.

In the bull test referred to, the difference in feed intake between the low testing RFI bull (in this case, a low RFI value is good) and the second highest RFI bull (again, in this case, a high value is bad) was a little over 3 pounds of feed per day.

If this is translated to a cow and her performance, that would equate to about  $54 of extra feed over the course of a 6-month winter-feeding period that the high RFI cow would consume compared to low RFI cow. 

Assuming they perform similarly in efficiency to the bull test. Fifty-four dollars per cow of feed savings would be fantastic! However, the cow consuming more feed also produced a calf that would perform 20 percent better than the low RFI cow. 

So if the low RFI calf weighed 500 pounds at weaning, the high RFI cow produced a calf weighing 600 pounds (again assuming that calf performance will reflect that of the bull).

With today’s cattle markets, even after considering an $0.08 slide, the heavier calf is worth about $96 more than the lighter calf. Simple math tells us that even after subtracting out the added feed costs, the heavier calf was worth $42 more than the lighter calf.

Steve Paisley, University of  Wyoming, has begun ranking bulls on test by RFI, as well as by a traditional ADG and feed to gain ratio. By combing these tests, a bull purchaser can see which bulls performed in the upper third of all three tests.

Those are the bulls that have the greatest potential to increase a producer’s profitability. It is also important to remember that an RFI ranking at a bull test is simply an index and only applicable for comparison of animals on that test. 

It is possible the bull with the best efficiency ranking in one test could end up middle of the road in another test, or even worse than the bulls/cows that you already own.

Please don’t misunderstand; RFI is a fantastic tool that allows beef cattle producers to make informed decisions about animal selection. However, it is a tool and should be used in conjunction with the other tools that producers already use for selection criteria. 

The assumption that cows and calves perform similarly to the bulls on test is not proven. Bulls are usually placed on a fairly high plain of nutrition in a lot. How does test performance translate to cows foraging on range grass or “limit-fed” hay during winter?

Considering the vast differences in physiological processes that occur for nutrient digestion and assimilation between a forage and grain diet, it is questionable if there is a direct correlation between efficiency measured with forage diets compared to grain fed diets.