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Mapping a route to better beef.

Mapping a Route to Better Beef

Rand McNally mapped America, noting the highways, byways, and everywhere in between. Now, finding the way from one city to another is as simple as checking a map.

Scientists with the Agricultural Research Service want to make cattle selection just as easy for ranchers. Researchers at the agency's Roman L. Hruska U.S. Meat Animal Research Center (MARC) will spend the next few years studying cattle's overall genetic makeup--called the genome--as part of a major livestock genemapping program.

The goal of the $2 million project at the Clay Center, Nebraska, facility is to identify genes at evenly spaced intervals along each of the 29 chromosomes that make up the bovine genome.

"It will be similar to the highway markers you see along the side of the road," says Roger T. Stone, a physiologist at MARC. "They will give us an idea of where we are, but we won't know what's in between."

Those markers could represent various production traits that are of economic importance to farmers and ranchers. They will also help researchers identify the genetic matter between the markers.

"By identifying genes or groups of genes that control production traits, the cattle industry will be able to produce beef for specific markets," says Dan Laster, director of MARC.

"This will also allow us to identify groups of genes responsible for resistance to diseases and parasites," adds Roger J. Gerrits, ARS National Program Leader for Animal Production.

"The gene mapping and evaluation program will accelerate the rate of genetic progress and will be essential to improve the quality and safety of food for human diets, as well as competitiveness of U.S. agriculture."

Eight scientists and support personnel are working on the project at MARC. Craig Beattie, a molecular biologist from the University of Illinois-Chicago, has been hired to head the project.

"This is truly a new era of science," says Gerrits. "Research with the bovine genome will accelerate our ability to improve reproduction, meat quality, disease resistance, and the metabolism of muscle and fat."

Most of the work will require the use of DNA probes to identify the gene markers. One class of probes will bind to a specific form of a gene known as an allele. For example, a probe with the genetic makeup for black coat color will seek out only that actual gene and not the alternative gene for red coat color.

Once marker genes have been identified, the maps will become an important basis for developing breeding programs. Breeders and researchers now rely heavily on statistical methods to identify animals of a specific genetic makeup.

"The maps are a place to start, not a place to reach," says Laster.

Knowing the genetic background of a calf could help identify which animals are likely to make the most efficient use of available feeds and produce the most tender meat. Gene maps could also assist producers in selecting animals that are best suited to a particular environment.

"Current technology enables scientists to splice, clone, and insert genes to change the genetic makeup of an animal," says Gerrits. "Mapping the bovine genome will also allow us to use these available technologies to improve livestock production."

Although the project is in its initial phases, researchers will not be starting from scratch. Scientists expect to make use of existing maps of the human and mouse genomes to build on current livestock gene maps, which are comparatively sparse.

The base sequences--chemical components--of cattle genes are the same as in humans about 80 percent of the time. Probes made from human DNA could bind to the equivalent bovine genes, speeding the mapping process. Bovine probes may also assist the human genome mapping efforts.

"About 200 bovine genes have already been identified, and researchers know where some of these genes are likely to be located on the different chromosomes," says Larry V. Cundiff, leader of the Genetics and Breeding Research Unit at MARC.

Roger Stone has isolated and sequenced seven genes related to disease resistance in cattle. Known as the bovine major histocompatibility complex, or MHC, the genes are similar in structure and genetic diversity to those of the human and other animal species.

The studies by Stone and former ARS colleague Noelle Muggli-Cockett began in 1985 and used the human genome map and DNA probes.

The goal of the disease resistance portion of the genome research is to improve the overall health of livestock without compromising desirable production traits like growth, reproduction, or meat quality.

However, as researchers attempt to use gene maps and related technology to improve production, special attention should be paid to the potential impact of the selection process on disease resistance.

"A producer may be unknowingly selecting animals with decreased disease resistance when selecting for increased production," says E. Travis Littledike, leader of the Animal Health Systems Research Unit at MARC.

"Disease can become a major limiting factor determining herd size. The larger the herd, the more stringent the requirements for sanitation, hygiene, and effective vaccination programs become," Littledike adds.

To zero in on genes related to disease resistance, researchers will first have to separate environmental effects from immune effects and determine the physical attributes that can contribute to diseases such as hoof anatomy to foot rot. Then, genetic resistance can be attacked from two angles--immune response and physiological factors.

Mapping may also assist researchers in their efforts to fight diseases such as bovine viral diarrhea, which cost producers millions of dollars each year.

For instance, identification of the receptor gene locations in the bovine genome that code for the BVD virus receptors on cell surfaces would promote studies of how these genes are regulated. If probes were available for these genes, then selection of cattle resistant to BVD may be possible.

"Genetic improvement of disease resistance is going to be a long, slow process," Littledike says. "It's not the answer in the short run, but in the long run, it will be worth the effort."

In the meantime, management practices, especially hygiene, will continue to play a key role in minimizing the incidence of disease.

Scientists anticipate the genome mapping project and other related research will provide considerable amounts of useful information and technology within 10 to 15 years.

Laster expects the research to make tremendous contributions to the livestock industry. "Once the genes are mapped, we'll be better able to move animal germplasm from one country to another," he says.

Not only is the information expected to be useful to cattle producers and related industry, but it may also be of value to researchers mapping the genome of plants and other animals. Conversely, ongoing research to map those genomes may assist bovine mappers in their efforts.

Gerrits says one goal of the genome mapping program is to put all of the information into a database that can be used by scientists at federal, state, and private research facilities. An international database to link scientists throughout the world may also be developed in the future.

PHOTO : Using a DNA probe, animal physiologist Roger Stone examines film showing genotypes of specific animals. (K-4287-10)

PHOTO : Veterinary scientist Travis Littledike analyzes the effect of trace minerals on animal resistance to disease. (K-4287-5)
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Title Annotation:part 1
Author:Gerrietts, Marcie
Publication:Agricultural Research
Date:Nov 1, 1991
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