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Virginia Cooperative Extension -
 Knowledge for the CommonWealth

PSS and Show Pigs

Livestock Update, December 2001

Scott Purcell and C. M. Wood, Animal & Poultry Sciences, VA Tech

The national and global market for pork has caused intense competition among producers. Although increased selection pressure for superior muscle growth has created tremendous gains in meat production, many undesirable and potentially deadly traits may be linked to the favorable genes and the traits they express.

One of these unfavorable traits is porcine stress syndrome (PSS). Discovered in 1968, it is a genetic mutation that causes pigs to become extremely stressed under conditions normal pigs can handle. PSS pigs tend to be lean and heavily muscled animals, but die suddenly when stressed. The pigs breathe rapidly, shake, their body temperature rises, and they eventually collapse with rigid muscles and die (Clutter et al., 2001). In addition, pork from PSS pigs is frequently pale, soft, and exudative (PSE). Meat that is PSE is undesirable and producers may receive less money for those market hogs.

Porcine stress syndrome is a homozygous recessive genetic trait. To exhibit PSS, an animal must have both recessive alleles (nn). The heterozygote (Nn) does not exhibit PSS, but is a carrier for the disease, and can have offspring that are PSS positive. There is a genetic test available that can determine the exact genotype of a pig (Stalder et al., 1997).

Current show ring standards may contribute to the frequency of the PSS genotype because PSS carriers can exhibit the lean, heavy muscled characteristics of a PSS pig (, 2001). In a survey of Texas shows done by Sterle et al. (2001), almost 50% of 97 class winning barrows were either carriers or homozygous for the stress gene. All breeds tested were equally likely to carry the gene. While these hogs might win shows, the meat from the positive pigs is likely to be PSE, and heterozygous gilts can spread the mutation into a herd.

Porcine stress syndrome is an important economic consideration in the swine industry. The breeding of hogs to for heavy and lean muscling has been a major factor in maintaining the genetic frequency of the stress allele. The tendency for PSS pigs to yield PSE meat is an important fact to consider for any producer. These economic factors should be weighed against any positive traits that PSS hogs might exhibit. It does not matter if the live hog looks good. If the pig does not live through the marketing process, or if the meat is of low quality, the producer will not make as much money.

Works Cited

Clutter, A. C., R. G. Kauffman, and L. L. Christian. 1999. Porcine Stress Syndrome (PIH-26). Purdue Univ. Coop. Ext. Serv., W. Lafayette, IN. 2001. Fugate showpigs. Available at: Accessed Oct. 1, 2001.

Stalder, K. J., L. L. Christian, M. F. Rothschild, and E. C. Lin. 1997. Maternal performance differences between porcine stress syndrome normal and carrier Landrace females. J. Anim. Sci. 75:3114-3118.

Sterle, J. A., C. L. Skaggs, and D. B. Griffin. 2001. Frequency of the porcine stress gene in show pigs and its effects on meat quality. J. Anim. Sci. 79:(Suppl. 1):73 (Abstr.).

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