Cow efficiency correlates with calves
STORY BY DR. JIM WHITE 
For any given level of average daily gain, we also want to understand efficiency in gain. So we measure a feedlot animal’s actual dry matter intake minus the animal’s expected dry matter and use the result as a measure of feed efficiency. This measurement is referred to as Residual Feed Intake, and, as in golf, a lower number is better. Cattle with low RFI are cattle with high efficiency; they used less feed than expected to gain weight. Cattle with a higher RFI took more feed to gain weight; they are less efficient. If an animal ate just as much as was predicted, the RFI is zero. Animals with an RFI below zero will have improved feed-to-gain ratio and a lower maintenance requirement. Low RFI has not been associated with any significant effect on backfat thickness, nor yield grade nor quality grade. There seem to be genetic differences, particularly comparing beef to dairy feedlot steers. Holstein steers tend to have relative high RFI values with a trend toward less desirable grade characteristics when compared to, say, straight bred Angus animals.
Given that in the feedlot feed efficiency is a tremendously important characteristic, there has been interest in knowing if the RFI of the feedlot calves is associated with the RFI of the parents. We would think that it is, because RFI is inheritable—the kink in the logic is that the feedlot calves are fed out on high-energy feedlot rations whereas the dams are nearly always maintained on much lower concentrate diets. There was work done in central Alberta measuring the RFI of cows on a high forage diet. The work was out of Lacombe, which is about halfway between Calgary and Edmonton, i.e. right in the middle of the windswept, usually frozen Canadian prairie. These were big Canadian cows. That’s mid-gestation cows that weigh more than 1,600 pounds. The cows were individually measured for feed intake over a 12-week period. Body condition scores were similar between groups, and remained similar, with cows being between a BCS of 5 and 6. Half the cows were in either the high or low group.
The diet for the cows was over half straw, 40 percent barley silage, and about a pound and a half of supplement. The
Cow efficiency rating
| | High | Low |
Average age, years | 5.4 | 5.8 |
RFI, lbs, day | -3.3 | 5.9 |
DMI, lbs, day | 28.9 | 36.4 |
Weight, lbs | 1,645 | 1,649 |
ADG, lbs | -0.05 | +0.06 |
diet calculated out as 8.5 percent protein with a TDN in the high 40s, and an ADF level of about 50 percent. It was a relatively high fiber, lower energy mid-gestation cow diet. Even so, high-efficiency cows ate 20 percent less dry matter than low efficiency cows. While not seen during the trial in question, the observations from the researchers were that, over time, high-efficiency cows tended to be in better body condition score, which makes intuitive sense. High-efficiency cows have lower maintenance requirements so they would tend to sock away more energy as fat stores.
The cows’ calves were fed out in a feedlot. The finishing ration was 75 percent barley, with silage and supplement; a 12 to 13 protein, 0.58 NEg type of ration. The feedlot performance of the calves is separated by the grouping of their dams.
As shown above, the calves of high-efficiency cows consumed 1.8 pounds less dry mater per day—roughly 10 percent less feed a day than the calves from low-efficiency cows. This converts into improved feed to gain and thus lower cost of gain. Carcass traits are unaffected. In the language of a PhD egghead like myself, this translates as, “the phenotypic and genetic correlation of RFI with carcass merit were not different from zero.”
Cow efficiency rating
| | High | Low |
RFI, lbs, day | 0.2 | 1.3 |
DMI, lbs, day | 18.3 | 20.1 |
Feed: gain | 6.3 | 7.1 |
ADG, lbs | 2.9 | 2.8 |
Backfat, inch | 0.27 | 0.30 |
Some of the RFI effect may be due to differences in rumen microbial ecology; efficient animals have higher rumen concentrations of certain volatile fatty acids. We will routinely shift the rumen fermentation toward higher efficiency by using balanced rations and including certain feed additives such as Bovatec.
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