Most cattlemen have felt the impact of rising input costs over recent years. Although prices moderated or fell at the end of 2008, perhaps one of the most noticeable increases last year was feed prices. Typically, feed makes up the greatest portion of non-fixed costs for cow-calf producers and 65 percent to 70 percent of total beef production costs. Therefore, seemingly small improvements in feed efficiency can result in dramatic cost reductions. This reality, along with new technology, has led many researchers to take a new look at feed efficiency.
In the past, improved feed efficiency was considered a byproduct of selection for increased growth rate. However, this method is biased in that faster growing animals are usually larger and therefore have increased energy maintenance requirements. Even when considering mature size differences, not all animals have identical metabolic efficiency, resulting in slow genetic progress.
Directly selecting for feed efficiency requires measuring the feed intake of each animal, which was difficult and expensive in the past. However, new technology has made measuring individual feed intake practical and is now being used to enable a new approach to improving feed efficiency - residual feed intake (RFI). RFI is defined as the difference between an animal's actual feed intake and their predicted feed intake, the prediction being based on equations for maintenance and growth requirements. RFI is independent of mature size and growth rate, and allows animals within a contemporary group to be ranked from most to least efficient. An animal with a negative RFI value is more efficient than average, and, conversely, an animal with a positive RFI value is less efficient.
Researchers have found considerable variation in RFI among animals, even within the same breed. In addition, RFI heritability estimates are similar to growth performance traits, suggesting that RFI can be meaningfully improved through genetic selection. In calves that have similar growth rates, there can be as much as 8 pounds of difference in feed consumed per day between the least and most efficient calves (Basarab et al., 2003). That results in large differences between efficient and inefficient animals. At an average feedlot cost of gain of $0.80 per pound ($0.13 per pound of feed); the actual cost of feed could vary by over a dollar a day. Over a 120-day finishing period, that could be as much as $125 difference in feed costs per animal. In addition, dry matter intake can vary as much as 21 percent between efficient and inefficient cows grazing summer pasture, with no difference in performance (Meyer et al., 2008). That can make a big difference when it comes to stocking rates and feed costs on ranches.
Many bull test stations are already using this new technology to collect individual animal intakes and report RFI values. Initial steps have been taken to establish EPDs based on RFI data, and progressive ranchers will use RFI data when selecting seedstock animals. Producers will still need to use a multiple trait selection strategy, but RFI can and should be incorporated into the parameters used to make targeted genetic improvements.