# Lower consumer prices: Project would save billions of dollars in costs at feedlots

Want a cheaper hamburger or a better priced quality steak? A newly started research project could save feedlots billions of dollars in feed costs and lower the cost of beef to the consumer.

The project, a joint effort between the Texas Agricultural Experiment Station and Texas Tech University, is looking for genetic variation in beef cattle bio-types that are directly related to how efficiently a given animal converts feed into pounds of quality carcass.

Researchers at College Station, Amarillo, Overton, McGregor, Uvalde, Vernon and Texas Tech are looking at stress responsiveness and something called residual feed intake (RFI).

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.

Feed conversion, sometimes called feed efficiency, is a useful tool, but it has limitations. High feed conversion is inherited but closely connected to growth rate. Consequently, when cattle breeders select animals with high feed conversion they often also select for bigger mother cows.

Larger mother cows take more feed to maintain, and consequently overall efficiency of an operation is not always improved. Also, the larger carcasses of cattle with higher growth rates can pose problems for beef processors who need a product that can be standardized for retailers.

The reason for this problem is that feed efficiency measures only how much feed is required for a pound of gain. 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 and growth rate.

For example, steers that weigh more and gain faster would be expected to consume more than steers that weigh less and gain more slowly.

In terms of RFI, a negative number is good. Animals that eat less feed than predicted would have a higher net efficiency and a negative RFI. On the other hand, animals that eat more feed than predicted would have a positive RFI and a lower net efficiency.

Simply put, Texas researchers are trying to understand why some animals eat less to gain the same as others, according to Dr. Gordon Carstens, associate professor with the Texas A&M Department of Animal Science and initiator of the study.

“We hope to learn whether steers that eat less than predicted do so because they have lower maintenance requirement,” Carstens said. “More efficient steers may require less energy for maintenance because they have an inherently lower basal metabolism or because they expend less energy due to lower activity rates.”

Australian researchers have shown that RFI is inherited to some degree. Texas researchers suspect from the Australian and other studies that RFI may highlight net feed efficiency differences independent of growth rate or mature size. Environment and stress play a role, too, so researchers are looking at how the action of an animal's natural metabolic hormones interact with RFI to affect weight gain.

Once animals are identified as having a high net feed efficiency independent of size and growth rate, then researchers can look for genetic markers unique to a low RFI, and select for animals that are efficient at converting feed to body weight without the undesirable carcass characteristics.

“We don't know if this is going to work or not. Some research in Australia indicates it might, but there is skepticism,” said Dr. Ron Randel, who is based at the Texas A&M University Agricultural Research and Extension Center at Overton. “The potential savings to the Texas beef industry are so high, however, we can't ignore the possibility.”

Randel, an international authority on beef cattle physiology, will initially be looking at the stress effects on RFI.

Cattle are stressed whenever they are moved, shipped, or run through chutes for vaccination. It has long been known that stress adversely affects an animal's metabolism and its feed efficiency. Like humans, some animals handle stress better than others, and the differences may be genetic.

To examine correlations between stress and RFI, Randel is looking at levels of growth hormones, insulin and cortisol, a stress-related steroid produced by the adrenal gland. Blood samples are taken before and after an animal has been given an injection that simulates the stress experienced when the animal is moved or handled.

“As functions of the adrenal and other systems depend upon hormone-mediated expression of important genes, we hope to be able to find genetic markers related to growth,” Randel said.

Most of the early RFI measurements are being done at College Station and the McGregor Center with 180 steers. The steers will be fed individually so their intake can be accurately measured. For the stress study, Randel is working with steers of a similar biotype.

The 180 steers will be separated into those with high, medium and low RFI. An equal number of the three RFI level animals will go to an experiment station feedlot at Amarillo and to the Texas A&M Agricultural Research and Extension Center at Uvalde. The Amarillo animals will be individually fed out for slaughter while the Uvalde animals will be grazed. RFI measurements will be continued on both groups.