Most livestock producers are aware that stress can have a major impact on growth, reproduction, handling and temperament. But stress can also affect carcass and meat quality characteristics, including meat color, product losses and palatability. As a producer of a consumer-driven product, it is important for beef producers to understand that management decisions at the producer level can affect the end product being presented to the consumer.
In order to understand how antemortem decisions can influence postmortem carcass qualities, let’s explore how muscle is converted to meat. Muscles obtain energy for activity from glycogen. Directly after death, circulation stops and the conversion of the muscle-to-meat process begins. This process is led by the conversion of glycogen in the muscle to lactic acid, and the carcass and meat become firm (rigor mortis).
Lactic acid is important to the creation of meat that is tender, tasteful, exhibits visually appealing color and does not spoil. If an animal is stressed before or during slaughter, the conversion of glycogen to lactic acid is altered, and meat quality is adversely affected. Many of the management decisions you control can influence the stress an animal experiences during their time before slaughter.
Some of these choices include the production facility animals are taken to, genetic selection, feed and nutrition management, how animals are treated while receiving care, techniques used during movement and transportation decisions. Moreover, some of the decisions made on the producer’s part, like the type of slaughter facility chosen, may reduce or increase the stress an animal experiences right before harvest. Let’s discuss some impacts animal stress has on carcass and meat quality.
The change in color and texture of meat is one of the most prevalent indications that an animal has been stressed, either short or long term.
Beef displaying pale, soft and exudative characteristics. Photo courtesy of Travis O’Quinn, Kansas State University.
- Pale, soft and exudative (PSE) meat is caused by severe, short-term stress that occurs just prior to slaughter. Some areas where severe short-term stress can arise are during the stunning process, rough and chaotic handling, transport and mismanagement of animals in holding pens before slaughter. Under these stressful situations, excessive glycogen is used postmortem, and a buildup of lactic acid occurs. Due to the buildup of lactic acid, the pH of PSE meat is considerably lower (5.4 to 5.6) than the muscle of an animal that was not exposed to stress (7.2). A lower pH causes meat to be pale, to be dry after cooking and to have poor flavor. This meat is undesirable for consumers and retailers.
A beef ribeye from a dark, firm and dry beef carcass. Photo courtesy of Jeff Savell, Texas A&M University. - Dark, firm and dry (DFD) meat is found in animals that have endured long-term (greater than eight hours) stress. Long-term stress can occur to the animal during long periods of extreme heat, fighting in holding pens, continued use of electrical prodding and exposure to unfamiliar environments. Any of these incidences can result in the rapid breakdown of glycogen in the muscles before harvest which, in turn, creates less lactic acid during the conversion of muscle to meat. The meat is darker in color and drier compared to animals that have a normal breakdown of glycogen and production of lactic acid postmortem. This meat is less flavorful, has an undesirable color to consumers and has a shorter shelf life due to a higher pH (6.4 to 6.8).
Tenderness has been touted as the most important factor for determining consumer satisfaction when eating beef. While flavor is indeed affected, decreased tenderness in meat from stressed animals has garnered more research. Genetics, animal age, feeding practices, gender and breed all play into tenderness. However, postmortem influences can reduce tenderness if an animal has been severely stressed. As touched on before, rigor mortis is only the beginning of the change in a carcass from muscle to meat. During this conversion, many enzymes within the meat begin breaking down the proteins in the muscle. The fibers of the muscle (myofibrils) are degraded by these enzymes.
There are several enzymes involved in improving the tenderness of meat post-rigor, but one of the main enzymes involved in postmortem tenderization are calpains. The pH and availability of glycogen in muscle postmortem influences the activity of calpains. This means when animals are stressed and their glycogen is depleted before or during slaughter, the pH will be altered and the meat will have less enzyme activity, ultimately producing a less tender product for the consumer.
Additionally, there is evidence that stressful conditions can cause calcium to transfer to the fatty tissues from the blood. The loss of calcium into the fatty tissues is important because calcium has a crucial role in activating enzymes that will break down muscle myofibrils. If less calcium is available in the muscle postmortem, fewer enzyme pathways are activated, resulting in less myofibril breakdown, which leads to less tender meat.
Because stress can potentially impact so many aspects of cattle quality, making decisions that lower stress in our production facilities is extremely important. The question that might be circulating around is: What can be done in order to minimize stress so meat quality is not impacted?
Multiple facets of a production practice can be altered to help lower stress in cattle before and during harvest. It has been observed that animals can be prepared to handle the stress of movement and handling by utilizing irregularity in management. This could look different for different production operations but could include introducing animals to new environments, playing music and alternating people in a feeding operation. Managing long-term stress in cattle might mean:
- Incorporating low-stress handling techniques
- Lessening the use of cattle prods
- Utilizing efficient and calm treatment techniques by staff
It is also noteworthy that stress susceptibility is a heritable trait in cattle. If it is apparent certain offspring have a flighty disposition that may impact meat quality, it may be of use to investigate their genetic conformation and make breeding decisions based upon temperament. Furthermore, it is the duty of a producer to ensure the slaughter facility that is conducting the handling, holding, moving, preparation, restraining and stunning of their animals is utilizing best practices for cattle harvest. Recognizing how stress affects meat and carcass quality is important for all to understand so efforts can be made to guarantee the best product in the end.
