Stressed pigs result in low quality pork with less value
Pigs’ meat quality can suffer from stress up to the time of harvest.
More so than with beef, the quality of pork can be heavily influenced by the conditions a pig faces immediately before slaughter, which makes attention to animal welfare critical until the end of the animal’s life, said Davey Griffin, PhD, professor of animal science at Texas A&M, during Pork 101 at the International Production and Processing Expo.
“Animal welfare is not just the right thing to do, it improves the quality of the pork, and that affects the farmer’s bottom-line,” said Griffin.
A major reason pigs’ meat can be influenced by stress up to the time of slaughter is that they have only one stomach, like humans, he said. Changes in pigs’ biochemistry happen rapidly. Any shocks to their system aren’t buffered by the reservoir of food and water held in the multiple stomachs of cows.
Summer-time heat stress in finishing pigs can result in a subsequent higher incidence of related declines in pork quality, he said, especially during transport. Every year, there is a general decrease in pork quality harvested during the peak of summer heat.
In general, identifying a stressed pig can be difficult, Griffin said. Genetic testing of pigs has helped to identify certain genes that influence a pig’s reaction to, which has allowed breeders to select for more resistant pigs.
However, breeding can only go so far. Along with this, pig farmers have improved their practices to reduce stress on the pigs, he said. Knowing pig’s biological instincts can help with this. Something as simple as putting a light in a darkened pen can encourage pigs to enter, since they instinctually try to move from dark to bright areas.
Pork quality declines caused by stress
When pigs are stressed immediately before slaughter, their meat tends to suffer from PSE, which stands for pale, soft and exudative, said Griffin. The meat will drop in pH more rapidly and this acidity causes the meat to become pale. The pork will also be more watery, but this liquid is then lost during cooking resulting in tougher meat. This happens because the short-term biochemical reaction to stress in the pig’s body doesn’t have time to recover before harvest.
Long-term stress, such as animal welfare issues on the farm, can result in DFD pork, or dark, firm and dry, he said. In these cases, the physiological response of the pig to stress has been triggered so much that it results in a persistent change in the muscles and subsequently to the pork.