Tri-State Neighbor: South Dakota Farm Newspaper

Consider the marketing potential producers could have if they knew in advance how their cattle would perform in the feedlot and on the rail. Animals that they knew would finish and marble well could be directed to premium programs. Others that had a genetic propensity for producing a leaner end-product could be sorted out and finished for markets they were better suited to.

While some of that sorting and predicting how cattle will perform is done already, it is still much of a guessing game. But several new DNA tests are now becoming available that identify specific performance-related genes - and aim to ultimately add efficiency and consistency to the beef industry.

GeneSTAR Marbling and GeneSTAR Tenderness were the first genetic tests of this kind to be offered to the United States beef industry and were unveiled about two years ago. Last September, a DNA test called Igenity Lª was made available by a division of the animal health company Merial. Other companies are following suit and more DNA tests for a variety of genetic traits are expected to be launched in the next year.

So what information do these tests provide and how can seedstock and commercial producers utilize that information?

"DNA testing offers producers a way to get information sooner and for less expense than progeny testing for these types of traits," said Susan Knights Willmon, with Colorado-based Genetic Solutions, the company that offers the GeneSTAR tests in North America. "Like expected progeny differences (EPDs), the genetic information revealed by GeneSTAR tests is one more selection tool available to producers for breeding cattle that produce a desirable end-product for consumers."

How do the tests work?

The DNA testing process is possible based on genomics research which has identified cattle genes and their function. Although the entire genetic code for cattle has yet to be mapped, as researchers identify specific genes that influence production traits, DNA tests can be conducted by using hair or blood samples from an animal to determine the presence or absence of those genes. Such is the case with the GeneSTAR Marbling, GeneSTAR Tenderness and Igenity L tests. Each test identifies a specific gene related to a production trait.

For example, GeneSTAR Marbling tests for the thyroglobulin gene, which previous research has shown to account for about 10 percent of the phenotypic variation in marbling - considered a large effect by researchers. The DNA GeneSTAR Marbling results indicate whether the animal being evaluated has two copies (homozygous), one copy (heterozygous) or no copies of the high marbling form of the thyroglobulin gene. This means animals with two copies of the gene would have a higher likelihood of expressing genetics for marbling. One United States study found that calf-feds with two copies of the thyroglobulin gene accounted for 12 percent more USDA Choice grade carcasses than animals with one copy and 19 percent more than animals with no copies.

The GeneSTAR Tenderness test identifies variants of the calpastatin gene, a naturally occurring enzyme that inhibits normal meat tenderization during post-harvest aging. Based upon Australian gene marker research, the GeneSTAR Tenderness test identifies two variations of the calpastatin gene - one associated with increased tenderness and the other associated with increased toughness. As with the marbling test, tenderness tested animals are identified as having two copies, one copy or no copies of the gene. Homozygous presence of the favorable calpastatin gene would indicate that these animals have a higher propensity to produce tender meat.

The Igenity L test determines which form of the leptin genotype an animal carries. Leptin is a protein that regulates appetite, energy use and marbling in cattle. For example, animals with the form of leptin called L-ccª have a diminished appetite. Animals with the leptin form called L-tt remain in a "hunger mode" and if managed correctly, this will allow them to reach harvest weight sooner and develop more marbling. Animals with the form of leptin called L-ctª are intermediate in their appetite and marbling. Research trials show that the form of leptin can have a big impact on cattle finishing performance. In a Texas trial of Charolais-Angus cross steers, only 11 percent of the cattle identified as L-cc graded USDA Choice while 62 percent of L-tt cattle earned that grade. In dairy cattle, the leptin protein impacts dry matter intake and appetite as well, resulting in an increase in milk production - about 1,000 pounds more milk per lactation from L-tt animals.

Using the DNA data

Once the DNA test results for a specific gene or traits are available for an animal, producers can then utilize that data to make selection and marketing decisions that fit their herd goals. For instance, by selecting animals with two copies of either the thyroglobulin or calpastatin gene - or both genes - producers could potentially increase the marbling and tenderness performance within future generations of their herd, said Willmon. Mating a bull and a cow that both have homozygous (2-star) ratings would pass on the desirable genes to 100 percent of their progeny.

Similarly, the Igenity L test can be used to make marketing and/or breeding decisions, according to Chad Jorgenson of Davis, Calif., and an independent sales representative with Igenity of Merial.

"The Igenity-L test identifies a specific DNA trait with 100 percent accuracy. Because it is an exact science, it is a good tool for producers to gather information on live animals and then make marketing and/or breeding decisions," he said.

For instance, he said that if producers are aiming for grid premiums they'd want to select sires and replacement females that are identified as L-tt genotype (those with higher genetic propensity for increased appetite and marbling). If their goal is to target lean yield programs, they'd want to select animals with the L-cc genotype.

But, although these DNA tests afford an exciting glimpse of future animal performance, the information they provide also comes with a dose of caution.

"We promote these DNA tests as one piece of information to use with the other selection tools available, such as ultrasound data or EPDs," said Willmon.

That caution is issued for several reasons. First, the thyroglobulin, calpastatin and leptin genes are each only one of the genes associated with marbling and tenderness respectively. Until the entire genetic code for cattle is mapped and other genes that impact these traits are identified, selecting for the presence of these individual genes is only a partial indicator of expected animal performance.

Secondly, no DNA test will ever guarantee the phenotypic expression of a desired trait - like marbling or tenderness in this case - any more than an EPD can. But it does allow producers to select and manage with a higher degree of accuracy.

Growing appeal

Already, response to this new technology has been "tremendous" said Willmon. She reports that about 15,000 cattle worldwide have been DNA tested using the GeneSTAR technology.

Merial also reports there has been a lot of interest from producers in using the new Igenity L test.

"Many producers realize the potential this information offers. It's also an added marketing tool for seedstock producers," said Sue Hoffman, who works with producers to conduct the test.

She points out that several cattlemen are already advertising sires that have been tested and offer a specific genotype.

For producers interested in testing their herds, Hoffman suggests starting by testing bulls and replacement females.

"This will give a base of information about what type of calves their herd is producing," she said.

Once that information is known, management and breeding selection decisions can be made to meet the producer's herd goals.

For example, calves could be sorted into groups based on their specific genotype and fed, managed and marketed into more uniform groups. If the cowherd presents a mix of genetics, they too could be sorted into groups and mated to appropriate sires to meet herd goals for marbling and/or tenderness.

Most importantly, Gary Veserat with Merial, emphasizes that these tests do not identify "good" or "bad" types of cattle.

"There is no one desirable genotype. If your market is for lean red meat yield, then L-cc or L-ct are the genotypes important to you. On the other hand, if your market is producing for a Choice grid, the L-tt genotype is probably most important to you. Producers should realize this DNA test provides information that allows them the opportunity to manage for the genetic potential of the animal and the goals of their program," said Veserat, who provides technical services to producers for Igenity.

Like Willmon, Veserat underscores the fact that DNA tests are simply another management tool.

"Environment and management still influence how the animal will perform, no matter what genotype the animal has," he said.

But when used with effective management, these new DNA tests should help producers realize increased profit by grouping cattle of similar genotype into properly managed groups. And ultimately, increased consistency and uniformity in the food chain should help better meet consumers' demands.

DNA testing for specific genotypes can be determined from an animal's hair follicle, milk, blood or semen. Hair follicles tend to be easiest to gather and handle for producers and there are fewer concerns about shelf life of the samples. On average, cost for a single DNA test ranges from $60 to $90, with discounts given for volume orders.