If you’re going to market a high-quality product, your hogs are going to have to be Napole and stress negative,” says Steve Moeller, Ohio State University swine geneticist.

This comes after additional evidence that the Rendement Napole (RN) gene causes pork quality problems worthy of concern. The data comes from Rodney Goodwin, the National Pork Board’s research director, who looked at the status and impact of the Halothane 1843 (porcine stress syndrome) and RN genes on 1,202 pigs from 1999 through 2001. The 548 gilts and 654 barrows were part of the Checkoff funded National Barrow Show Sire Progeny Test and includes eight pure breeds. Each sire group in the study involved eight pigs that represented at least three litters.

All pigs were slaughtered at an average weight of 240 pounds. Carcass lean muscle quality and quantity measurements were collected after being chilled 24 hours. The Iowa State University Meats Laboratory ran additional evaluations on pork chops from each carcass. The university’s nutrition and food science laboratories also conducted lipid, cooking and sensory panel tests on the pork chops. (See tables.)In terms of the stress gene: “ These results agree with past research,” notes Goodwin. “ The negative pork quality effects of the Hal-1843 gene overwhelm the slightly greater carcass lean content, so the gene should be eliminated.” The industry decided to rid the U.S. swine herd of e stress gene back in 1996. However, as you can see by the NBS data, that goal still has a ways to go.

As for the Napole gene – once thought to be a Hampshire-only concern – it was found in all but two of the breeds in the study. “We’re finding it (the RN gene) migrating through the breeds,” says Moeller.

From a carcass standpoint, the RN gene has no impact on lean muscle or fat composition, but it is detrimental to lean quality. These latest data confirm what French and Swedish researchers also have found.

“The negative effects on pork quality are low ultimate pH, paler meat color, reduced marbling score, softer meat, greatly increased drip loss and cooking loss,” notes Goodwin. “The high drip loss is particularly undesirable for case-ready pork products; and then there’s the additional product yield loss due to much greater cooking loss.”

“Economics favor elimination of the RN gene due to these processing losses.” Moeller agrees, “any time you have clear, negative data as you have here, combined with previous data, it supports elimination of the Hal-1843 and RN genes.” That’s especially true if you want to tap any number of niche markets. Even if you’re not planning to tap a niche market, your packer may have the RN gene on his radar screen along with Hal-1843.

The RN gene can cause processing yield losses of 3 percent to 6 percent in loins and hams. That’s bad news for packers. Their margins are tightening just like they are on the farm, and packers will continue to look for ways to salvage what they can. As pH measurements become more commonplace, it will tell the packer as much about your animals’ RN gene status as it does Hal-1843. The RN gene produces a low ultimate pH – in the neighborhood of a 5.4 to 5.5 pH, depending on the day and slaughter conditions.

“The producer needs to understand that these effects show up in the carcass and it costs the packer money,” says Moeller. “If your pigs don’t meet the standards then you’re going to face a discount or loose market access.” Some packers have already told some producers that they no longer want their hogs based on the carcasses’ pH results.

The study looked at purebred hogs, but that’s not to imply that all purebreds
present a concern. That’s certainly true about both the Hal-1843 and the RN genes. Many purebred producers are testing their herds for both genes in an attempt to eliminate them.

Most commercial seedstock companies are offering RN-negative options in their “muscle-quality” sire lines. However, ask to take a look at the Hal-1843 and RN status of the terminal lines. It will vary between companies.

With the release of a DNA test for the RN gene in May 2000, testing for both the stress and RN genes is easily accessible. The cost runs about $40 for a Hal-1843 and $50 for an RN test from Geneseek in Lincoln, Neb., the only RN-certified lab.

Ask your seedstock supplier to provide pedigree verification or DNA test results for these genes on any boar or semen that you’re planning to use in your breeding program. The industry’s approach to the RNgene has been to eliminate Hampshire genetics. But not all Hampshires carry the gene, and this study shows not all other genetic lines are RN-free.

The majority of pork has been further processed for years, and that’s where the RN gene takes its greatest toll. Now, with the dramatically growing trend of pumped and case-ready products, as well as goals to increase export sales, Napole’s time is up.

The Napole vs. Stress Effect
Both the Rendement Napole gene and the Halothane 1843 gene impact pork quality by dropping the pH of the lean muscle. However, the pH declines differently.

With the stress gene, lactic acid builds up quickly in the muscle causing a rapid decline in the pH – within the first hour or so postmortem.

With the RN gene, the pH decline is related to an increased glycogen level in the muscle, which leads to increased lactic acid production. This occurs during the first 24 to 48 hours postmortem, thereby dropping to what is known as the ultimate pH.

In both cases, the muscle fibers break down so that the fibers lose water. In the stress gene’s case, the rapid breakdown of muscle fibers creates toughness. In RN’s case, the degradation over a longer time period can make the tissue slightly more tender, when cooked. Also, in fresh muscle, RN-positive hogs start off with a slightly higher water content, so even though they lose a lot of water, they still may end up with a slightly higher juiciness score. That’s not the case with the stress gene.

Regardless of the muscle’s final water content, in both cases the muscle’s structure won’t allow the fibers to bind water, which means adding water or a pump solution will be ineffective.