How to prevent and treat porcine stress syndrome? A detailed guide to practical methods
Porcine stress syndrome is a nonspecific stress response triggered in pigs by stimulation from various adverse factors. It occurs mostly in pigs kept in confined housing or awaiting slaughter after transport, and manifests as death or, after slaughter, pale, soft pork with water exudation, thereby affecting meat quality. It occurs frequently both in China and abroad and brings huge economic losses to the pig industry. Let us take a look below at the prevention and treatment methods for porcine stress syndrome!
Causes of porcine stress syndrome
1. Environmental factors: It mostly occurs when pigs are stimulated by certain adverse environmental factors in feeding management, producing a stress response to improve the body's adaptation to the internal and external environment. Common stressors that can cause a stress response include infection, trauma, poisoning, high temperature, noise, transport, hunger, hypoxia, regrouping, transport, mating, farrowing, and so on. These stressors stimulate the body, causing the pituitary——adrenocortical system to produce specific disturbances and nonspecific defense responses, resulting in stress syndrome.
2. Genetic factors: It most commonly occurs in lean-type, muscular, short-legged, round-thighed and solidly built pigs, such as Pietrain pigs, Poland China pigs and certain lines of Landrace pigs. Pigs whose red blood cell antigen is the H system blood type are also mostly stress-susceptible pigs. Susceptible pigs are more easily startled and difficult to handle, and often show trembling of the muscles and tail.
Symptoms of porcine stress syndrome
1. Sudden death stress syndrome: It mostly occurs when strong stressors such as transport, preventive injection, breeding and farrowing stimulate the pig, and the pig dies suddenly without any clinical symptoms. Postmortem lesions are not obvious.
2. Malignant hyperthermia syndrome: Excessive body temperature, flushed skin, sometimes with purple patches, cyanotic mucous membranes, generalized trembling, muscle rigidity, difficulty breathing, tachycardia, and tachyarrhythmia until death. After death, rigor mortis appears, the carcass decomposes faster than normal, internal organs appear congested, there is pericardial effusion, and pulmonary congestion and edema. This type of disease occurs mostly in crowded and hot seasons, when death is even more severe.
3. Acute back muscle necrosis: It mostly occurs in Landrace pigs. After exposure to stress, when the acute syndrome lasts about 2 weeks, the affected pig shows swelling and pain of the back muscles, with the spinous processes arched up or bent to the side, and is unwilling to move position. After the swelling and pain subside, the diseased muscles atrophy, while the vertebral spinous processes protrude. After a few months, some degree of regeneration may appear.
4. Pale pork type: The affected pig initially shows rapid trembling of the tail, generalized rigidity with muscle stiffness, and irregular pale and red patches on the skin, which then turn cyanotic. There is difficulty breathing, even open-mouth breathing, elevated body temperature, and death from collapse. After death, rigor mortis sets in quickly, the joints cannot be flexed or extended, and necropsy shows that some muscles are pale, soft and exuding water. At 45 min after death, muscle temperature is still 40°C and pH is below 6, whereas normal pork pH should be above 6. This is related to excessive postmortem glycogen breakdown and lactic acid production; the muscle pH drops rapidly, pigments are lost and water-binding capacity is reduced. This kind of meat is not easy to preserve, and the quality after cooking and processing is poor. Some pork becomes darker red than normal, called "dark, firm, dry pork" (that is, DFD pork). This situation is mostly seen in pigs that have been starved during long-distance transport.
5. Gastric ulcer type: Stress in pigs causes vigorous gastrin secretion, forming autodigestion and leading to erosion and ulceration of the gastric mucosa. In acute cases, the exterior appears well developed, the pig is prone to vomiting, the gastric contents are bloody, and the feces are tarry. In some cases there is massive gastric bleeding, body temperature drops, the mucous membranes and body surface skin become pale, and the pig dies suddenly. In chronic cases, there is poor appetite, weakness, sluggish movement, sometimes abdominal pain, an arched back while lying prone, and passage of dark brown feces. If the stomach wall perforates, secondary peritonitis and death follow. Some pigs are found to have gastric ulcers only at slaughter.
6. Acute enteritis and edema type: The commonly seen clinical conditions such as piglet diarrhea and porcine edema disease are mostly caused by Escherichia coli and are related to the stress response. This is because during the stress process the body's defensive function is reduced, and Escherichia coli becomes a conditional pathogenic factor, leading to a nonspecific inflammatory pathological process.
7. Chronic stress syndrome: Because the intensity of the stressors is not great, the reactions caused by continuous or intermittent repeated exposure are mild and easily overlooked. In fact, they have already formed adverse cumulative effects in the pig's body, reducing its production performance and weakening its defensive function, making it susceptible to secondary infection and the occurrence of various diseases. The blood biochemical changes before death are elevated serum lactic acid, decreased pH, and increased creatine phosphokinase activity.
Prevention and treatment of porcine stress syndrome
1. Treatment: The principle is sedation and supplementation of corticosteroids. First move the pig to a non-stressful environment and spray the skin with cool water. Pigs with mild symptoms can recover on their own, but pigs with purple skin and muscle rigidity must be given sedatives, corticosteroids and anti-stress drugs. For example, chlorpromazine hydrochloride can be chosen as a sedative at a dose of 1-2 mg/kg body weight, once by intramuscular injection, or diazepam at 1-7 mg/kg body weight, once by intramuscular injection. Vitamin C, sodium selenite vitamin E mixture, diphenhydramine hydrochloride, sodium salicylate and others may also be chosen. Use antibiotics to prevent secondary infection, and intravenous injection of 5% sodium bicarbonate solution can be used to prevent acidosis.
2. Prevention: ① Genetic breeding and selection work should be strengthened; through the halothane test or creatine phosphokinase activity testing and blood typing, stress-susceptible pigs should be gradually eliminated. ② Minimize the pressure on pigs from stress factors in all aspects such as feeding management that cause disease. For example, improve feeding management, reduce various noises, avoid excessive cold or heat, humidity and crowding, and reduce various stimuli such as driving, catching and anesthesia. During transport, avoid crowding and overheating; before slaughter, avoid driving and stimulating pigs with electric prods. Before stress may occur, use sedatives such as chlorpromazine and diazepam and supplement selenium and vitamin E, thereby reducing the mortality caused by stress.