26 March 2008

5 minute read

North America

At stake, literally, are steaks, as well as and hamburger and ribs. Eating less and gaining more means more efficient beef cattle operations, which could eventually mean a better product on grocery store shelves, said Dr. David Forbes, AgriLife Research animal nutritionist.

Forbes, who is based at Dr. Gordon Carstens, AgriLife Research animal nutritionist (College Station); Dr. Ron Randel, AgriLife Research animal physiologist (Overton); and Dr. Tom Welsh, AgriLife Research reproductive physiologist (College Station).

At the heart of the subject is a beef-animal measurement technique called "residual feed intake," or "RFI" in research shorthand.

RFI has been used to fine-tune poultry operations for years, Forbes said. More recently, researchers have found that the technique can be applied to beef cattle. More importantly, they have found there are differences between animals of the same breed, even the same herd, when it comes to how efficiently they convert feed into gaining weight.

What makes the study different is it is designed to develop a means of measuring RFI of cattle on pastures, Forbes said.

"We will test cattle on pasture so that we can use this technique to clarify and validate the residual feed intake data we're obtaining from feedlots," Forbes said.

RFI is not to be confused with feed conversion, a measurement used by animal scientists and agricultural producers for decades to improve net efficiency in poultry and swine operations, Forbes said.

Feed conversion is a relatively simple calculation that measures how much feed an animal consumes to gain a pound, Forbes said. It's simple mathematics: weight of the feed consumed daily divided by the weight gained daily.

The math behind RFI, however, is more complicated. RFI compares the difference between an animal's actual feed intake and its predicted feed intake. Predicted feed intake is the amount of feed the animal is expected to consume based on its weight, growth rate and the performance of its contemporaries. For example, steers that weigh more and gain faster would be expected to consume more than steers that weigh less and gain more slowly.

"Residual feed intake is better than feed conversion as it (residual feed intake) is independent of growth and body weight," Forbes said. "Residual feed intake measures the variation in feed intake that remains after the requirements for maintenance and growth are accounted for, and is calculated as the difference between an animal's actual feed intake and the feed an animal is expected to consume based on its body weight and average daily gain."

For either measurement, keeping track of an animal's feed intake in a confined feeding operation is relatively simple. Computerized equipment tracks an animal's intake by various measures, usually involving feeding stations that are keyed to an electronic device either hung around the neck or clipped to the ear.

All such measures done to date have been done in some kind of confined feeding operation or another, Forbes said.

But unlike chickens and swine, beef cattle spend more time in pastures than in confinement. As valuable as a research tool as RFI is for feedlots and researchers, questions remained: Can RFI of cattle on pasture be measured? And if it can be measured, how would pasture RFI match up with RFI data collected in feedlots? Forbes and his research partners are trying to find answers to both questions. "(With this method), when they're on pasture, can we measure forage intake," Rouquette said. "And the question we'll be asking is does that RFI pasture rating hold true to what we measure in the feedlots?"

If the data compare, then the easier-to-acquire feedlot data can be used to select animals that perform better in the pasture, Rouquette said.

The project is an example of research only an agency such as AgriLife Research is equipped to do, Forbes said.

"A private individual, if he knew half his animals were more efficient, he'd get rid of the others pretty quickly," Forbes said. "But as scientists, we're interested in the less efficient animals too, because we want to understand the biology."

Through understanding the biological processes behind residual feed intake, it may one day be possible to identify less efficient animals via a simple test, Forbes said.

"But that's a long way off," he said. "Right now, we are just trying to solve basic measurement problems."

The researchers are near to having solved the first problem, that of developing the methodology of measuring residual feed intake of animals on pastures.

Twice a day, the animals are fed a corn gluten supplement containing alkane, a waxy substance similar to paraffin. Forages also contain alkanes. Using an instrument called a gas chromatograph, fecal samples from the test animals can be analyzed for amounts of the different alkanes.

"Using the ratio of those two different alkanes, we can determine how much (grass) the animals have eaten," Forbes said. Forbes is confident that the methodology he and his research team have chosen will work, he said. There are details yet to be resolved, however, before the actual test can proceed.

"What we don't know yet is how many fecal samples we need to get to adequately describe intake over these long periods. We' ll dose these animals for periods up to 70 days, which is an incredible undertaking in itself," Forbes said.

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