Dr. Patrick J. Gunn, Iowa State beef cow-calf extension specialist, recently presented his evidence at the Driftless Region Beef Conference held in February in Dubuque, Iowa.

Gunn and other researchers are using residual feed intake (RFI) as a main indicator of feed efficiency. RFI has gained traction among researchers, centralized bull test operators and seedstock producers as the primary benchmark for feed efficiency.

Gunn said, “RFI is defined as the difference between actual feed intake and the feed intake predicted on the basis of the animal’s gain and maintenance requirements for its bodyweight. RADG (residual average daily gain) is defined as the difference between actual weight gain and the gain predicted on the basis of dry matter intake, maintenance of bodyweight and fat cover."

"Both RFI and RADG are calculated using an equation formed from actual gains, feed intakes, average weights on test and fat cover of an animal’s herdmates.”

Although it is well proven that selection for RFI can improve feed efficiency in a herd, questions exist on how RFI may interact with fertility and longevity. Since the animals eat less than expected, research is needed to see if cows will eat enough to maintain body condition and lactation – and still have acceptable reproductive rates.

Gunn said, “There is little doubt that both volatile input costs and cattle prices will continue to place an emphasis on more efficient cattle. Therefore, the use of RFI as part of a selection program is likely here to stay."

"The question now shifts from whether or not RFI is good or bad, but rather how to utilize RFI as part of a larger selection process.”

The traditional thinking of many producers is that smaller cows are more efficient, but data show this is not always the case. Gunn said there is a wide variability of feed efficiency between animals, and he cited a study which showed ranges of raw feed-to-gain ratios ranging from 10-to-1 to 4-to-1 in a group of animals where no selection for feed efficiency has been practiced.

“This variability makes selection with favorable outcomes possible over a relatively short amount of time,” Gunn said.

“Some research in the U.S. is being aimed at proving or disproving that selection for RFI in the cow herd is a good thing. However, almost all current U.S. data would suggest that RFI does not impact fertility and longevity in the cow herd,” he said.

“When we circle back around to the data that is created from a feed efficiency test, all measurements and calculated efficiency indicators are correlated to each other with the exception of ADG (average daily gain) and RFI,” Gunn said.

“If we can select for cattle that eat less than expected (desirable RFI) while also having above-average ADG, we would like to suggest that we are selecting for cattle that can do more with less, perhaps even in a more extensive environment. If this is the case, we might expect that such females would have improved longevity within the herd.”

Although intense selection for a single trait in a breeding program is generally frowned upon because negative impacts are typically noted in other production parameters, Gunn said, “An astute cattleman will blend new selection opportunities with other traits that help them meet their production and marketing goals.”

Although RFI has been shown to be a moderately heritable trait, at this time no phenotypic indicators of RFI have been discovered.

Gunn and assistant scientist Dr. Garland Dahlke of the Iowa Beef Center – Iowa State University have been researching and observing the herd at the Werner Family Angus in Diagonal, Iowa, on a pilot project. (They hope to work with other herds in the future.)

Data collected over the last seven years on more than 500 heifers on Werner Family Angus support the idea that concurrent selection for RFI and ADG increases longevity.

The Werners have developed their grazing herd with the goal of delivering little or no supplemental feed to the herd. All heifers go through their feed efficiency system. (GrowSafe System Ltd., Calan Broadbent Feeding System and IDology Gain are some of the more commonly used systems.)

About 25 percent test for desirable RFI and above-average ADG, and Gunn said the Werners found those females that meet this criteria to have better yearling pregnancy rates, and a greater proportion of them make it past 3 years old. This is of particular interest to the Werner family as getting first-calf females to rebreed in this low-input system has been one of their largest production quandaries.

“When we select for desirable RFI/high ADG females, this data indicate that those females are not any different in size at birth, weaning or as a yearling and do not differ in their milk or genetic indices,” Gunn said. “While this selection theory needs to be tested on a larger scale and more locations, we believe that using RFI as part of a multi-trait selection process does have the opportunity to improve feed efficiency of the herd while at least maintaining, if not improving, fertility and longevity.”

The need for efficiently produced, sustainable food is not only needed with a growing world population, but consumers are also demanding it. The feed efficiency of beef cattle (6 pounds of feed to 1 pound of gain) is the lowest of commonly consumed meat proteins compared to pork (3 to 1), chicken (2 to 1) and fish (1 to 1).

Cattle, however, have the ability to convert less digestible grain byproducts and forage into protein, keeping beef a competitive product for consumers.

Since feed costs have historically been 50 percent or more of the cost of raising beef, Gunn said it is logical that improvements in feed efficiency would result in not only overall production efficiency and profitability, but also improve global food security as the world population continues to grow at a rapid rate. 

A “Feed Efficiency Calculator Tool” is available online.

Kelli Boylen is a freelance writer based in Iowa.

PHOTO: Cattle efficiency through residual feed intake will grow more prominent as prices for calves and feedstuffs grow more volatile. Staff photo.