Extensive research on the effects of the RN gene on pork production, especially on pork quality, has been carried out worldwide since it was discovered. Studies on the impact of the RN gene on fresh and processed pork quality have consistently shown that the RN gene has negative effects on meat pH, WHC, colour, drip loss, cooking loss and processing yield.
The negative effects of the RN gene are a result of a dramatic increase in glycogen levels in the muscle of live pigs that have the gene. Glycogen is the form in which sugars are stored, particularly in liver and muscle. After slaughter, muscle glycogen is converted to lactic acid, which lowers the muscle pH. Therefore, the more glycogen the muscle contains, the more lactic acid will be produced and the lower the ultimate pH of the muscle will be. The increased lactic acid levels may result in muscle pH dropping below 5.5 within 24 hours after slaughter. This low and dramatic drop in meat pH causes a breakdown in protein, which results in pale muscle colour and poor WHC in the meat.
The "acid meat" condition is very similar in characteristics to the pale, soft and exudative (PSE) pork condition caused by the PSS gene. In fact, when the PSS
gene is present, it intensifies the effect of the RN gene on meat quality.
Figure 1 illustrates the relationship between meat quality and post-mortem changes in muscle pH in normal pork, acid pork, PSE pork, and dark, firm and dry (DFD) pork.