P orcine stress syndrome (PSS) is an inherited neuromuscular disorder in pigs (6). The PSS condition is controlled by a defective gene which results in three possible genotypes (normal, carrier and positive). The PSS condition was first described by Topel et al. (38), who noted physically stressed, susceptible pigs would collapse in a shock-like state and die (Figure 1). Much attention has been given to how the PSS gene affects the muscle quality and performance of market hogs since its discovery. Increasing consumer and packer demand for lean meat has led to an increase in the use of terminal sires with one or two copies of the PSS gene by market hog producers, because of its perceived advantage in producing lean, heavy-muscled hogs. A large proportion of the homozygous recessive (nn) PSS-positive animals, and heterozygous (Nn) animals carrying one copy of the PSS gene, produce carcasses with inferior muscle quality (10, 32). Debates continue in the popular press concerning the use of the PSS gene, particularly in terminal sire lines.
Molecular biology advancements have resulted in the development of a simple and relatively inexpensive procedure to determine the PSS genotype of animals, with accuracies approaching 100 percent (13). Swine producers can submit blood samples from individual pigs to a licensed laboratory, and have PSS genotype determined by the molecular method. Individual swine producers can then determine the appropriate use of the PSS gene to meet their breeding objectives.
"PB1606-Porcine Stress Syndrome," The University of Tennessee Agricultural Extension Service, PB1606-500-2/99 E12-2015-00-202-99, http://trace.tennessee.edu/utk_agexani/41