The effect of stress on pork quality is a very important issue in pig farming that needs to be treated on time.

Environmental and management factors that affect animal welfare have several consequences for the animals. The effect of heat stress on pigs affects multiple organ systems, including the immune system. Hormones and molecules released during a stressful event impact the normal immune system response to pathogens. This event makes animals more susceptible to infection.

How is pork quality defined?

Pork quality is classified according to the properties and characteristics of the product. Pork products are ultimately preferred by consumers according to their perception. Pig farming must guarantee high-quality meat to obtain good yields and favorable results in the market.

There are mainly three types of natural characteristics that define the quality of pork. The first characteristic is the physicochemical properties such as pH, color, texture, water retention capacity. The second characteristic corresponds to organoleptic properties such as softness, consistency, flavor, odor. These are qualified by experts and are largely perceived by the public. Finally, there are the microbiological properties, which show the hygienic quality of the meat.

There are external factors to the animals that determine the quality of pork. It is recognized that there is an effect of the type of feed supplied, the breed, the production system, the transport conditions, the state of health, and the handling. These last characteristics, added to slaughter, can have certain levels of stress on the animals.

The ideal classification for pork quality is RFN (Red, Firm, and Non-Exudative). The effect of stress on pork meat can cause the physicochemical and organoleptic properties to be affected and, consequently, the consumer rejects this type of meat. The affected meat can be pale, soft, and exudative (PSE). Also, because of stress, the meat may become dark, tough, dry (DFD).

Effect of stress on meat pork quality

The effect of stress undoubtedly has an impact on pork quality. This physiological condition, under certain conditions, can become a pathological condition if the response is disproportionate. An event that produces high levels of fear or anxiety in animals triggers the stress hormonal cascade.

Stress is a physiological response that all animals have developed as a survival mechanism. The adrenal glands are responsible for releasing hormones called catecholamines and cortisol. These two types of hormones generate responses throughout the pig’s body, including changes in meat quality.

For this reason, measurement of both hormones has been used to determine the degree of stress in pigs. These stress-regulating hormones increase blood pressure and decrease blood flow in the muscles. This effect can lead to ecchymosis and petechiae in the muscles. On the other hand, these hormones increase glucose metabolism in muscle, eventually producing lactic acid which changes muscle pH.

Chronic stress affects immunity

Events that produce chronic stress, such as improper feeding, inadequate management, or deficient animal welfare, must be considered. Acute moments of stress such as slaughter must also be carefully managed. In both cases (chronic or acute) there is an effect of stress on pork quality and various systems and organs.

Thus, states of stress sustained over time weaken the immune system of pigs. This deficiency predisposes animals to viral or bacterial infections such as PRRS, Influenza, Porcine Epidemic Diarrhea, or Rotavirus.

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Furthermore, infectious agents that cause diarrhea in pigs also favor chronic stress states. Some of the pathogens involved in this are Salmonellosis, E. coli, Circovirus, Clostridium, Coccidiosis, and Rotavirus.

Other agents associated with chronic stress are those causing Porcine Nephropathy and Dermatitis Syndrome (PNDS) and Transmissible Gastroenteritis (TGE). This last microorganism affects neonates more severely. These diarrheal diseases affect the general and special immunity of the digestive tract of pigs.

Currently, immunostimulant pronutrients are being developed, which are molecules of vegetable origin that boost the immune system. These molecules strengthen both innate and acquired immunity in pigs. These immunostimulant pronutrients administered to sows have shown favorable results in terms of the number of piglets born alive, lower mortality during gestation and lactation. These complex molecules also increase the antibodies in the sows’ colostrum, thus protecting the pigs from infectious diseases such as Porcine Epidemic Diarrhea.

Porcine Stress Syndrome

Porcine Stress Syndrome is a genetic disease, it is a recessive monogenic hereditary disease. It has been associated with an alteration in the ryanodine receptor gene (Ryr1). Pigs with this genetic variation can die instantly under high levels of stress. The signs observed in them are dyspnea, hyperthermia and upon death, they rapidly go into rigor mortis. The quality of pork meat is affected because this disease causes muscle necrosis.

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Critical points in swine stress

There are critical points that can end pork quality. Therefore, they must be considered at all times of production up to the moment of slaughter.

1. Management: It is advisable to guarantee management based on animal welfare, as this avoids swine stress. This management includes familiarizing the pigs with human presence, the correct size of the facilities, prohibiting physical punishment practices.
2. Welfare and health: the best sanitary status should be achieved in swine production. Ensuring that the farm is free of diseases and maintains the best welfare indexes significantly reduces stress during production. Disease processes (infectious, traumatic, nutritional) increase the effect of stress on pork.
3. Ventilation: Pig house ventilation is a fundamental parameter to consider. Environmental contaminants can affect the respiratory system and increase stress in pigs.
4. Fasting before transport: pigs undergo a fasting period to evacuate all intestinal contents before slaughter. Other advantages of this practice are to avoid dizziness, vomiting, and bronchial aspiration during transport. However, fasting should not be done for long periods because hunger stresses the animals.
5. Transport: this is considered the most critical moment because it is when accidents or high levels of stress occur in the pigs.
6. Slaughter: An important moment that determines changes in meat, for example, is slaughter. Pre-mortem handling is a critical stage that must be carefully managed to avoid stress in the animals. Poorly managed slaughter generates a level of stress that triggers the hormonal response and changes the properties of the meat.

What can be done to reduce stress in pigs?

To maintain good pork quality, it is essential to solving all the causes of stress in production.

1. Establish adequate vaccination and deworming schedules to prevent infectious and parasitic diseases because they increase stress.
2. Respect the population density on the farm and during transport to avoid trauma and fights that affect the quality of the pork meat.
3. Ensure proper ventilation of the farm and maintain environmental parameters in optimal ranges to provide animal welfare to the pigs.
4. Establish clear transport protocols and comply fully with them, to avoid stress and damage to the pork.
5. Ensure the correct stunning before slaughter like an animal welfare practice.
6. Implement Good Swine Practices and slaughter protocols that are in line with animal welfare.

CONCLUSIONS

The quality of pork meat is a characteristic of utmost importance for pig farming since it is ultimately perceived by consumers. Physical, chemical, and microbiological characteristics should always be ideal for pork.

Sometimes, stress can affect this quality of pork, due to the physiological response produced by hormones released during a stressful event. In addition, if this state is chronic, it can weaken the immune system of the animals, predisposing them to infectious diseases.

On the other hand, there is a pathology called Swine Stress Syndrome that causes muscle necrosis in genetically predisposed individuals.

Thus, to avoid all the negative effects of stress on the quality of pork meat, prevention measures are established in the critical points of pig production. This makes it possible to obtain high-quality meat that is well perceived in the market.