Stress Gene

The stress gene comes from Pietrain pigs on 

Carrier hogs cannot be shown in sanctioned breeding shows.

The "stress" gene is a common term used to describe a gene mutation that was first identified over 30 years ago, due to physical effects visible in hogs with the mutation. These hogs were identified as having Porcine Stress Syndrome (PSS), which is characterized by the pig's inability to adapt to stressors such as physical exertion, transport, or fighting. Animals exhibit extreme nervousness and excitability. The inability to adapt often results in sudden death. If pigs survive until slaughter, the stress gene is associated with a higher yield of lean meat, but also poorer quality meat that is pale, soft and exudative (PSE).

Genetically, the stress gene is identified by the letter "N" which indicates normal or "n" which indicates the mutated form. Normal ("N") is the dominant form. The animal's genotype indicates which form of the gene was inherited. The three possible genotypes are:

  1. NN: This represents a normal hog that is not affected by stress characteristics. The hog inherited a "normal" copy from both parents.
  2. Nn: This represents a "carrier" hog - an animal that carries one copy of the stress gene. The hog inherited a "normal" copy of the gene from one parent and a mutated copy from the other parent. Although the "carrier" may appear normal, there is a 50 percent chance that the animal will pass the mutation on to any offspring.
  3. nn: This represents a "homozygous mutant" or "stress positive" hog. Both copies of the gene are mutated. These animals will likely exhibit the traits of PSS. If used as breeding stock, they will pass the mutation on to any offspring.

It is well documented that stress positive hogs produce carcasses that are leaner and heavier muscled than normal hogs, and that carriers are intermediate in muscling and leanness. Thus, at one time, "Nn" and "nn" sires were used in the commercial swine industry to capitalize on improvements in percent lean. However, research has shown that over 95 percent of stress positive hogs and 30-50 percent of carrier hogs produce PSE meat. This meat is very light colored, often almost gray or white, does not hold its shape and loses much of its moisture prior to cooking. The meat is undesirable because of appearance and inability to hold moisture. This results in a very dry cooked product.

15% of stress positive hogs will die when transported.

Last Updated: 2/22/2007 11:16:58 AM


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