PORK & PORK QUALITY
PIH-26
pork industry handbook
COOPERATIVE EXTENSION SERVICE • PURDUE UNIVERSITY • WEST LAFAYETTE, INDIANA
Porcine Stress Syndrome
Authors:
Dennis N. Marple, Auburn University
Lauren L. Christian, Iowa State University
Max D. Judge, Purdue University
Reviewers:
Richard J. Epley, University of Minnesota
Mrs. Wm. J. Heger, Jasper, Missouri
David E. Schafer, Kansas State University
The porcine stress syndrome (PSS) is a nonpatho-logical disorder that was a major concern to pork producers 10-15 years ago but has been less of a concern recently. The disorder, when present, is usually associated with heavily muscled animals and results in sudden unexplained death losses. Animals having PSS often show signs of nervousness and may have muscle tremors indicated by a rapid tremor of the tail. When these animals are exposed to a stressful situation such as a change in surroundings, a sudden change in the weather, vaccination, castration, estrus or mating, they often respond by becoming overly excited and developing blotches on their skin and muscle rigidity followed by rapid, labored breathing. Their body temperature also begins to rise and they begin to show signs of heat stress even in cold weather. At this point, many producers have attempted to save their animals by spraying with water, but the condition progresses so rapidly that it is virtually impossible to cool the animal fast enough.

Death losses from PSS usually occur during the process of sorting and delivering animals for slaughter. In addition, death losses are higher in the summer months when temperatures are higher, because these animals are unable to rid themselves of body heat. Research has revealed many characteristics of these animals. Some of these findings will be summarized in this fact sheet.
Genetic Factors
First, it should be established that no breed is entirely free of the PSS problem and, likewise, no breed can be categorically termed stress-susceptible. Current theories suggest that the genes controlling the PSS trait are
recessive in that both the sire and the dam must be carriers of the gene or genes responsible in order to get stress-susceptible offspring. Therefore, if there is a problem in the herd, the quickest and most economical step is to replace the sire with one you can confidently predict is not stress-susceptible or a carrier of the disorder. Although the PSS condition is sometimes found in animals with superior muscling, it is not necessary to sacrifice carcass merit for freedom from the PSS problem. Instead, one should incorporate meat type animals into the breeding herd that do not appear to be of the PSS type.

Tests for PSS
It is now possible to objectively evaluate candidates for the breeding herd by using one of two tests The first test involves catching a small drop of blood on a special card* or in a test tube and analyzing for creatine phosphokmase (CPK), a serum enzyme that is abnormally high in PSS swine. The serum test requires submitting the blood sample to a hospital or laboratory with CPK testing capability. It is important that the blood obtained for these tests be drawn at least 2 and preferably 8-12 hours following a physical stress such as a 100-yard run or 5-mile truck ride. Second, the blood must be taken from an ear vein or some other superficial vein so the blood sample is not contaminated with muscle tissue. Third, exercise care in handling the animals since test results will be inflated if the animal has sustained muscle bruising from fighting or harsh treatment prior to sampling_____________
* Genetic Information Systems. Box 515. Elk Grove Village. Illinois. 60007
Cooperative Extension Work in Agriculture and Home Economics, State of Indiana, Purdue University and U. S. Department of Agriculture Cooperating. H. A. Wadsworth, Director, West Lafayette, IN. Issued in furtherance of the Acts of May 8 and June 30, 1914. It is the policy of the Cooperative Extension Service of Purdue University that all persons shall have equal opportunity and access to its programs and facilities without regard to race, color, sex. religion, national origin, age or handicap