The RN gene, also known as the Napole gene, or "acid-meat gene," has a major impact on meat quality. The effects of this gene have only been observed in purebred or crossbred Hampshire swine populations, according to University of Illinois (UI) researchers. The UI researchers recently collaborated with PIC to learn more about the effects the RN gene has on meat quality.

The cause of the "acid-meat" condition is higher-than-normal levels of glycogen in the muscle of live animals. After slaughter, muscle glycogen is converted to lactic acid, which results in muscle with lower-than-normal ultimate pH. At these low pH levels, the meat is paler and the water-holding capacity of the muscle is reduced.

There is no current DNA-based test available to differentiate between genotypes of pigs. Differentiation must be predicted on the basis of a phenotypic measurement of muscle glycolytic potential (GP). Glycolytic potential is a measurement of all the compounds within the muscle, including glycogen, glucose, glucose-6-phosphate, and lactate, that can be converted into lactic acid. Glycolytic potential is an effective measurement used to distinguish between animals which are homozygous normal (low GP) or those animals which carry one or two copies of the dominant allele (high GP).

The UI researchers determined the glycolytic potential of the longissimus muscle in 72 pigs. Animals were split into three groups based on glycolytic potential of either high, moderate or low potential.

No differences between the low, moderate and high groups were detected for growth performance and carcass characteristics. However, significant effects were determined for meat quality attributes. Meat quality measurements such as longissimus ultimate pH, objective color scores, and water-holding capacity were significantly poorer for animals with high or moderate glycolytic potential levels compared to those with low glycolytic potential values.

Although animals with high glycolytic potential had poorer fresh meat quality, palatability traits were enhanced. Animals classified as having high glycolytic potential had improved tenderness and juiciness scores (determined by trained taste panel) by 15% and 8%, respectively. The high glycolytic potential animals had a 6% improvement in shear force when compared to pigs with low glycolytic potential.

In another recent study, conducted by UI in collaboration with the National Pork Producers Council, National Swine Registry, Ohio State University and Western Illinois University, the frequency of the allele which causes the higher-than-normal muscle glycogen levels was estimated at .63 within an American Hampshire population. This research indicates that 86% of purebred Hampshires carry one or two copies of the dominant allele. The Hampshire is used heavily as a terminal sire within the U.S. pork industry, meaning the RN gene, has the potential to play a major role in pork quality, researchers noted.

Researchers: K. Douglas Miller, Mike Ellis and F.K. McKeith, University of Illinois. Phone Miller at (217) 244-3147.