Animal Stress can be caused by various reasons. They include handling before and during harvest (loading and off-loading of animals), holding pens, and transportation. Weather conditions such as storms and temperature changes could also cause animal stress.
Fresh meat from stressed animals has higher levels of lactic acid. Higher lactic acid pre-harvest leads to pH levels of 5.4-5.6, typically Pale-Soft-Exudative (PSE) meat.
Using pH measurements to monitor animal stress related to handling might not be as accurate as measuring lactic acid from blood samples. On the other hand, the pH measurement is simpler, faster, cheaper, and does not require dealing with blood samples. The pH measurement is done on fresh meat, at line speed, either on the hot side (45 minutes after slaughter), or on 24 hours chilled meat (also called ultimate pH).
information related to reducing animal stress through proper
handling, equipment and facilities, please review Dr. Temple
Grandin's web page.
For excellent information related to meat quality, please visit Dr. John Forrest web page at Purdue University.