Effects of Pre-Slaughter Stress on Pork Quality
Livestock Update, December 2001
Jennifer Kitts and C. M. Wood, Animal & Poultry Sciences, Virginia Tech
One of the biggest pork quality problems is pale, soft, exudative (PSE) pork. Physiologically the quality of the meat is dependent upon its ultimate pH, which is determined by conversion of glycogen to lactic acid within the meat (Berg, 2001). A pig's genetic makeup plays a role in the incidence of PSE pork, but the amount and type of stress placed on the pig prior to slaughter is the main factor. Loading and unloading, transporting, mixing of pigs, and slaughterhouse practices are all aspects that should be managed to minimize stress and in doing so produce high quality pork.
An animal's stress response depends on its perception of the stressor (Morrow-Tesch, 2001). The pig's perception of the environment translates into psychological stress, which can be measured by concentrations of blood and saliva cortisol. A study comparing transportation effects showed that cortisol concentrations are higher after loading and stay elevated in pigs subjected to rough transport (Gade, 1997).
After being unloaded, the pigs are expected to walk in new surroundings and are placed in new pens. Extra physical stress is often placed on heavier muscled pigs because of unsoundness in the legs. In a review of slaughterhouse stressors, Faucitano (1998) found that improving facilities helps decrease loading time, therefore decreasing stress and improving meat quality. Additionally, increased physical movement as a result of fighting increased cortisol and creatine phosphokinase in the blood that ultimately results in a higher meat pH. He also noted that immediate slaughter or an extremely short resting period could increase the incidence of PSE meat by 40%.
Electric goads are often used as a means of control and movement of the pigs at the slaughter plant, causing an increase in adrenaline compounds in the blood and an increased rate of glycogenolysis, the breakdown of glycogen to glucose, ultimately resulting in a poor meat quality (D'Souza et al., 1998).
The results of recent scientific studies on pork quality should have a great impact on the entire swine industry from the producer to the packer to the consumer. The stress placed on pigs can be lessened with the proper management practices, which increases meat quality and benefits everyone.
Berg, E. P. 2001. Influence of stress in composition and quality of meat, poultry, and meat products. J. Anim. Sci. 79(Suppl. 1):849 (Abstr.).
D'Souza, D. N., F. R. Dunshea, R. D. Warner, and B. J. Leury. 1998. The effect of handling pre-slaughter and carcass processing rate post-slaughter on pork quality. Meat Sci. 50:429-437.
Faucitano, L. 1998. Preslaughter stressors effects on pork: a review. J. Muscle Foods 9:293-303.
Gade, P. B. 1997. The effect of pre-slaughter handling on meat quality in pigs. In: Manipulating Pig Production VI. p 109. Australasian Pig Sci. Assn., Werribee, Victoria.
Morrow-Tesch, J. L. 2001. The effect of management practices on the stress response in Livestock. J. Anim. Sci. 79(Suppl. 1):852 (Abstr.).