Cattle Today

Cattle Today

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by: Clifford Mitchell

Testing for DNA markers is a relatively inexpensive alternative to testing traits that are hard to evaluate. These tests provide an indication of future performance in a manner that allows the producer to keep genetics in production and not have to take the terminal route to identify potential success.

“We are genotyping traits that are very hard and expensive to measure. It is difficult for producers to select for these traits without genetic tests,” says Jim Tate, Global Marketing Manger for Igenity.

Testing for the leptin gene in livestock is a new cutting edge proposition associated with DNA gene markers. The IGENITY-L™ test, provided by Merial, allows producers to utilize yet another tool in beef production to improve carcass merit.

“Leptin is a protein produced in white fat tissue and the more leptin produced, the stronger the signal is sent to the brain to reduce appetite,” Tate says. “The leptin protein is directly related to appetite, energy utilization and fat deposition.”

According to Tate, the genetic variation for leptin can be expressed in three forms.

1) L-cc™-is considered normal for most animals. The protein expressed in this form will cause an animal to lose appetite and increase metabolism once desired levels of leptin are achieved. This genotype is also commonly associated red meat yield and larger ribeye area.

2) L-tt™-is common with animals that exhibit increased marbling and fat related characteristics because the signal to reduce appetite is less recognized by the brain. The animal keeps eating even with increased levels of leptin.

3) L-ct™-is the heterozygote form and falls somewhere in between the two extremes.

Each variation of the gene has its benefit to beef production. Based on the genetic makeup of the cow herd, management decisions can be made to improve the end product depending on the goal of the individual producer.

“If I know I have red meat yield then an L-tt sire is the obvious choice to improve marbling. All calves sired by an L-tt bull will exhibit at least one “t” (marbling) allele. An L-cc sire might be the choice if I need to improve red meat yield,” Tate says. “If the goal is to increase both the ribeye area and marbling then the Heterozygote (L-ct) could provide the answer. There are benefits to all genotypes.”

With Expected Progeny Differences in place in most breeds to identify carcass quality, some producers believe there is no need to test for this gene. Adding known genetic information to the EPD could confirm what these numbers entail or expose the unknown.

“EPDs often explain a high percentage of marbling. Now producers have another tool to identify this trait,” Tate says. “If you have high marbling EPDs, a L-tt result confirms that the EPD probably accounted for leptin genotype. An L-cc result may be more instructive to the seedstock producer because the leptin genotype wasn't accounted for in the EPD and it needs to be added to the genetic profile.”

By simplifying the results of the genetic tests, producers can take a practical approach to bull selection. These tests allow producers to place added selection pressure when it comes time to make a buying decision.

“Genetic tests are another tool to add to the mix used to purchase bull power. Weigh them accordingly to the type of end-product you want to produce,” Tate says. “Don't give up all the other traits just to have an L-tt bull walking the pasture.”

Future applications of known genotypes may help solve management problems. Producers holding this information may be able to better allocate costs and utilize feed resources, although this information carries little data to support these theories at this time.

“The difference in genotype might mean less days on feed for a L-tt to avoid problems with yield grade on a quality grid. L-cc cattle might be targeted for a lean grid to maximize profits,” Tate says. “To the cowman L-tt cattle might get by on less energy, while L-cc cattle may need extra energy to calve and breed on schedule.”

Knowledge is half the battle, according to Tate. By having known genotypes cattle can become more predictable, but management and sound husbandry will never be left out of the scenario.

“When you know the genotype you know if you can pass a gene on. When both parents possess the genotype, heritability of the genotype becomes 100 percent,” Tate says. “Genetics only account for a portion of the phenotype. The other part is management. We're helping explain the genetic part of the equation.”

There are three steps that should help increase profitability as gene markers are identified. Once genotypes are known they can be applied to selection, management and marketing.

“By knowing what you have, you can select genetics that will allow you to come closer to the desired goal and manage them better,” Tate says. “If I know what I am producing then I can also market them more effectively.”

Cost associated with DNA testing is the limiting factor for most beef operations looking to improve their end-product. Different circumstances exist for each producer, but the technology has its place in both purebred and commercial sector.

“The seedstock producer can't afford not to do it. The bulls we tracked this sale season with known genotype outsold their counterparts,” Tate said. “The commercial man should use bulls with known genotype then test his replacement heifers. If he replaces the herd at rate of 10 percent a year, in 10 years all his females will have a known genotype.”

As with most new technology there is a red flag. The silver bullet concept does not exist with knowing genotype, but DNA markers show great promise and add another perspective to the tools that are readily available to producers to make them more profitable.

“We are identifying one marker for marbling. GeneSTAR is another test available to producers that will identify another marker for marbling,” Tate says. “Marbling is a complex trait. In time there may be more markers that try to explain marbling. We have to look at how all the different tests work together.”

With the acquisition of Frontier Beef Systems, Igenity will have DNA tests available for tenderness, color, parentage verification, traceability and a data base to store DNA for use at a later date when more tests become available that are relevant to the end-product goal. To learn more about testing for the leptin gene go to


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