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UW study looks to discover heritability, rumen components of feed efficiency in sheep

by Wyoming Livestock Roundup

Buffalo – Melinda Ellison, a PhD student at the University of Wyoming, was one of the speakers at the Northeast Wyoming Sheep Symposium on Dec. 11. She provided updates on sheep research at the UW nutrition lab, under the direction of Kristi Cammack.

“In our lab, the main focus is feed efficiency,” she said.

Tests can be expensive and time consuming, so her team is looking for easy and inexpensive ways to test animals, she stated.

“Many producers try to select for feed efficiency in their flock, but it doesn’t always work out as well as they would like,” she said.

Ellison explained that an animal that has high feed efficiency doesn’t necessarily correlate with good production or good wool traits and that efficiency should be considered as an individual trait to be selected for.

Residual Feed Intake

“The feed efficiency measure that we are using at our lab is Residual Feed Intake (RFI),” she noted.

The value is calculated by comparing the amount an animal is expected to eat and the amount that it actually consumes.

“It is a little confusing because a negative RFI value actually correlates with positive feed efficiency,” she explained.

Ellison continued that RFI is not related to body size or average daily gain. Researchers can put animals from different maturity levels and different sizes into a group, test them and still get comparable results.

“At the university, we have a GrowSafe System,” she stated.

This system is a feed bunk with enough room for only one animal to put its head in at a time. The animals are given tags that are read when they use the bunk.

“The bunks are on scales, so everything the animals eat is recorded,” she said.

Bunk systems throughout the country are set up for cattle, Ellison explained. UW has the only bunk system set up for sheep, which makes her lab unique.

“We get daily graphs of what each animal eats, as well as behavioral data for the sheep,” she said.


One of Ellison’s trials compared RFI between two different diets.

She asked, “If an animal is highly efficient on a forage diet, will that be the case when you send it to the feedlot?”

 The sheep were given alfalfa pellets, and then the pellets were switched to corn.

“The animals that were less efficient on one diet seemed to be less efficient across the board,” she explained.

Sire testing

Ellison also said RFI is moderately heritable, so it could potentially be selected for to get higher production from less feed.

She explained that another team at the lab is working on a ram sire test.

“There is a wool breed test and a black-faced meat breed test with an index score,” she explained.

Average daily gain, staple length, fiber diameter and carcass data are gathered from the tests. 

Ellison explained that researchers are considering how feed efficiency might also be a useful trait to consider in those tests.

A blood sample is also taken from the rams during testing and studied for markers in the DNA that may correlate to feed efficiency.

“There have been positive results in this area. Researchers have found several genes of interest that seem to be related to feed efficiency,” Ellison said.

If those genes could be identified, she explained, then producers could send blood samples to a lab to receive data about their sheep.

Rumen bacteria

“Another thing we are looking at right now is ‘gut bugs,’” she said.

Ellison continued that in both animals and humans, the kind of bacteria that live in the gut seem to have a role in health and body maintenance.

“One of the things that we have started working on is looking at what type of bacteria are in the rumen of these animals,” she said.

Researchers have done a number of studies involving RFI testing in lambs. In one study, rumen fluid was extracted from the top eight most feed efficient animals and the eight least efficient animals.

“We send the fluid off for sequencing and to get numbers and types of bacteria to see if there is a profile or individual bacteria that makes a difference,” she explained.

DNA sequencing is becoming more cost effective, and Ellison believes that it has the potential to be a tool used by producers.

“The end goal would be, at some point in time, to send in a rumen sample, see what bacteria are in that animal and determine that it is probably more efficient,” she said.


Another study that Ellison is doing involves twin lambs, which are each given rumen fluid at birth. One twin is given fluid from a highly efficient animal, while the other receives fluid from a low efficiency sheep.

“We are hoping, when we do a feed efficiency trial on these twins, that they will diverge as high and low, based on the microbes we gave them,” Ellison explained.

If the study is successful, she believes that it could be possible to give lambs a pill when they are born that would make a difference in how the animal eats.

Financial impacts

“In our analysis, we have seen 20 to 26 percent increases in profitability based on feed, by choosing low versus high efficiency animals,” Ellison stated.

Trials typically last for 50 days, so looking at that data over a number of years could make a large financial difference.

“Feed efficiency may be hard to think about in the state that it is in now, but hopefully down the road, we can make it easy for everyone to work with,” Ellison said.

Natasha Wheeler is editor of the Wyoming Livestock Roundup and can be reached at

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