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Saturday General Session

Biological Variation in Feed Efficiency

Gordon Carstens

Gordon Carstens,
Texas A&M University

Profitability is simply a function of outputs and inputs. The beef industry has made great progress improving output traits, such as weaning weight and average daily gain, but very little progress has been made improving input traits, according to Gordon Carstens, professor at Texas A&M University, who spoke at the 2009 Beef Improvement Federation (BIF) symposium May 2 in Sacramento, Calif.

“As we have selected for larger, faster-growing cattle, we have also increased the maintenance requirements of the cows, so they eat more,” Carstens said, noting that 70% of a cow’s annual expense is due to feed, and 51% of that feed budget is consumed by cow maintenance needs.

Residual feed intake (RFI) has emerged as a selection tool to improve that input efficiency. RFI is a measure of efficiency that quantifies variance in feed intake unrelated to level of production. An efficient animal would consume less feed than expected given its growth rate and is therefore said to have a low RFI.

“Unlike ratio-based efficiency traits (such as feed-to-gain ratios) that are influenced by growth and maturity patterns, RFI is phenotypically independent of the production traits used to compute expected intake,” he explained. “This means that favorable selection for RFI will improve feed efficiency with minimal effects on growth or mature size.”

There are notable differences between cows with low RFI values and those with high RFI values, and the variation has a biological basis.

“Previous studies have estimated that approximately one-third of the biological variation in RFI of growing calves could be explained by animal-to-animal differences in digestion, heat increment of feeding, composition of gain and activity,” Carstens said, “and the remaining two-thirds was likely associated with cellular processes like ion pumping, protein turnover and mitochondrial function.”

High-RFI animals have lower digestibility, so they have to eat more to get the same absorption of nutrients. High-RFI animals have also been found to spend more time eating each day. Animals with low RFI compared to those with high RFI also have a 21% difference in energy expenditure each day.

Carstens said that while our understanding of RFI in growing cattle has advanced, we have limited knowledge of the associations between RFI measured during the early postweaning phase and the biological efficiency of mature cows. Little is also known about the influence of selection for RFI on other economically relevant traits, such as reproduction.

Editor’s Note: This summary was written under contract or by staff of Angus Productions Inc. (API). To request reprint rights contact Shauna Rose Hermel, editor, at 816-383-5270. PowerPoints are posted with permission of the presenter and may not be reproduced in whole or in part without the express permission of the presenter.

The 41st BIF Research Symposium and Annual Meeting was hosted by the California Beef Cattle Improvement Association and the California Cattlemen's Association. For more information, visit www.bifconference.com or www.calcattlemen.org/bif2009.html.


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