Role of Pre-harvest Handling of Pigs on WHC
Meat animals, like humans, respond in different ways to stress. "Stress-susceptible" animals cannot easily handle the loading, hauling, crowding, weather conditions, and the mixing with other strange animals. These animals respond by increasing their heart rate, respiratory rate, and muscle metabolic rate, all of which have negative effects on rigor mortis, protein denaturation, WHC, and meat functionality. Livestock producers may increase the population of problematic animals by using stress susceptible animals in their breeding programs. Producers often ignore or do not know how to handle the ante-mortem effects that contribute to lower pork quality. In addition, meat plant operations often do not know the ante-mortem history of each group of animals that they purchase. Thus, a more "systems" approach to marketing and slaughter of pigs can help maximize desirable meat processing procedures that minimize negative effects on the meat's WHC.
All animals should be properly handled ante-mortem, so abnormal quality is not induced even in pigs without the stress gene. In fact, about 8 to 15% of pigs not carrying the stress gene have some undesirable variations in quality traits at many plant operations. The most common causes for this are less than optimal handling practices, inadequate chilling, or a combination of both. Given that certain genes or other gene-related traits may cause variation in meat quality due to increased susceptibility to the physical and social challenges of hauling and lairage before slaughter, the entire system of ante-mortem conditions should be carefully monitored to minimize live animal factors from significantly influencing the WHC of meat.
Gentle, calm handling of livestock the last few minutes before stunning is critically important for preventing an undesirable increase in the rate of pH decline (which decreases WHC) early post-mortem. Electrical stunning is not necessarily worse than CO2 stunning for accelerating pH declines; but the group handling capability with CO2 stunning has some advantages. See Learning Resources 'Driving Pigs to Stunning' and 'Animal Welfare-friendly Housing Systems' for more information about handling and welfare issues for pigs.