Feed efficiency is affected by multiple factors

Casper – Producers want their cattle to gain weight and perform well while eating less, said Hannah Cunningham.

On Nov. 27 at the Wyoming Natural Resources Rendezvous, hosted by the Wyoming Stock Growers Association and Wyoming Association of Conservation Districts, University of Wyoming (UW) Ph.D. student Hannah Cunningham, discussed genomics and environment as factors that affect feed efficiency in cattle.

She also discussed residual feed intake (RFI) and feed conversion ratio (FCR) as major factors of feed efficiency.

Relative feed intake

“Producers can get in trouble by selecting cattle purely based on RFI, which can lead to cattle that don’t eat a lot and don’t perform well,” noted Cunningham.

“Cattle with high RFI are less efficient than cattle with low RFI. Feed intake is strongly correlated with RFI, which means high RFI animals eat more than low RFI animals,” she explained.

Multiple studies have found that Charolais and Limousin cattle are more feed efficient than Angus or Herefords, Cunningham mentioned, adding that doesn’t mean Angus and Herefords aren’t or can’t be efficient.

“Studies also indicate there’s a genetic component to feed efficiency, and both RFI and FCR are heritable traits,” according to Cunningham.

FCR for cattle ranges from 0.17 to 0.46, with RFI ranging up to 0.52, meaning 17 to 46 percent of FCR variation and 52 percent of RFI can be attributed to genetics, she explained.

“Animal geneticists have a good platform to find ways to select animals based on genetics for feed efficiency improvement due to research data,” she added.

Interactions

Cunningham stated researchers should examine the interaction between genotype and environment in feed efficiency research because the answer to feed efficiency is not one result or the other.

“Researchers should also look at how genotype and environment correlate with other important traits, like RFI and FCR,” she noted. “RFI and FCR correlate, which means if producers select more efficient cattle based on RFI, they also get cattle with a better FCR.”

She mentioned the genetic correlation between RFI and FCR is also dependent on the breed and diet of cattle, among other factors.

“RFI is independent of body size and growth, which is advantageous for producers because, no matter what, cattle size won’t increase,” she said. “There is a strong correlation between mature body size and FCR, which can be a problem for producers.”

Ideally, the most feed efficient cattle have a combination of several traits, Cunningham noted.

Genomics

“I think if researchers look at animal physiology at a more basic level and look at the genetic makeup of animals, there’s room to improve feed efficiency at the molecular level,” stated Cunningham. “Researchers know what they want for feed efficiency but don’t quite understand what happens to make animals more or less efficient.”

She believes using molecular physiology and genomics can improve the accuracy of feed efficiency estimates.

“If researchers focus on understanding variations, new markers for selection can be discovered,” Cunningham noted, adding that finding reliable feed efficiency markers is difficult because feed efficiency is a complex trait affected by many factors.

“A common goal for animal science researchers is to improve feed efficiency by looking at how the environment affects feed efficiency, including diet type, temperature, etc.,” Cunningham stated. “I propose focusing also on genotype or genetics.”

She also believes the rumen micro-biome should be examined to determine if it relates to feed efficiency.

Research

Cunningham participated in three different studies at UW, which have influenced her conclusions about feed efficiency.

“I’m hopeful for the future because research is improving feed efficiency predictions. It’s encouraging to see all the research dedicated to understanding feed efficiency,” she concluded.

The first study examined small intestinal physiology and how it related to RFI in finishing cattle.

Her second study investigated muscle and adipose tissue and what happened in the tissues to help mature cows respond better to nutritional stress.

The last study, currently in progress, evaluates the role of the rumen micro-biome, specifically how maternal factors influence the micro-biome, and how maternal influence might influence feed efficiency in progeny.

“In the small intestinal study, the question was whether organ mass differed in high versus low efficiency animals, simply because larger organs require more energy, and it also examined the relationship with intake,” Cunningham said. “The results showed the small intestine, omasum, kidney, liver, total gastrointestinal tract and stomach complex were larger in less efficient animals. Basically, high RFI, or less efficient cattle, consumed more feed.”

She added higher feed consumption provides more available nutrients, which may have increased the organ mass.

“With increased organ mass, there is also an increased energy requirement, which could explain why the organs were larger in the less efficient cattle,” she noted.

Muscle and adipose tissue

The muscle and adipose tissue study focused on the relationship between energy storage and release, according to Cunningham, who added both processes relate to feed efficiency.

“The muscle and adipose tissue study, where cows were restricted from feed then given free-choice feed, showed differentially expressed genes between the high and low gain cattle,” stated Cunningham. “By itself, the results don’t mean much, but they reveal a lot when looking at the function of the genes.”

During the restricted feed period, some genes were associated with pathways that modulate lipid and carbohydrate metabolism, and during the free-choice feed period, some genes were associated with cellular processes like immune responses and cell injury, according to Cunningham.

“I think the benefit of the study was realizing what happens in muscle and adipose tissue when feed is restricted versus free-choice feed,” she said. “Within the muscle and adipose tissue lies answers about why cows respond differently to various nutritional stressors.”

Rumen micro-biome

The ruminant digestive system is complex and unique, mentioned Cunningham, and without rumen microbes, ruminants wouldn’t be able to convert low-quality feed into high-quality products.

“This study focuses on the role of rumen microbes in feed efficiency and calf performance. Researchers are also asking whether the rumen micro-biome is subject to maternal influences that could affect long-term feed efficiency,” she stated.

Cunningham noted this study is in progress, but the hope is to determine if the maternal environment, pre- and post-calving, affects the rumen micro-biome.

“We want to try and identify microbes that are always associated with more efficient animals,” she said. “Perhaps, using the environmental effect on the rumen micro-biome and identifying efficient animal microbes could be used to shift microbial populations to improve feed efficiency.”

Overall, these studies look at feed efficiency, the scientific base of different systems and how molecular differences can drive changes in feed efficiency, according to Cunningham.

Heather Loraas is assistant editor of the Wyoming Livestock Roundup and can be reached at heather@wylr.net.