Most pigs on farms get through vaccination according to schedule without problems, but occasionally this happens: just minutes after being vaccinated, a pig suddenly breathes rapidly, its skin turns red or purple, and it foams at the mouth; it may even collapse and convulse. Many farmers’ first reaction is to think, “There’s a problem with the vaccine,” and they rush to give an injection to reduce the fever. They may treat a routine reaction as a serious illness, or lose valuable time needed to rescue an animal experiencing a true acute allergic reaction. The vast majority of immune stress reactions are not caused by vaccine quality defects. They are mainly caused by a combination of suboptimal health, improper vaccination procedures, cold stress, and individual allergic predisposition. Proper health screening and vaccination procedures can greatly reduce the incidence of adverse reactions.
First, distinguish which reactions are normal
and which require emergency treatment
A vaccine is itself a foreign stimulus to the body. Brief, mild discomfort after vaccination is a general reaction caused by the vaccine’s inherent properties. It does not mean that immunization has failed or that there is a problem with vaccine quality.
General reactions (normal reactions): Mild redness, swelling, warmth, or pain at the injection site; brief lameness in one limb; and, in some pigs, a mild increase in body temperature, faster breathing, reduced feed intake, or brief feed refusal. These reactions mostly occur within 48 hours after vaccination. Medication is generally not needed, and they usually resolve on their own.
Abnormal reactions (severe reactions/allergies): In a very small number of pigs, signs may occur shortly after vaccination, including restlessness while standing, inability to rise after lying down, difficulty breathing, congestion or swelling of the visible mucous membranes, muscle tremors, foaming at the mouth, collapse with convulsions, or cyanosis of the skin. Pregnant sows may abort (including premature delivery). These reactions are severe and require prompt detection and appropriate emergency treatment.
Adverse-reaction deaths: Death without treatment within 48 hours after vaccination, or death despite treatment. Qualified personnel must conduct an on-site investigation and assessment, establish a file, and trace the adverse reaction.
A key distinction: for a general reaction, the approach is “observe and provide care”; for a severe reaction, it is “act without delay.” The management approaches are completely different. Repeatedly giving injections for a general reaction as if it were a serious illness, or passively waiting when an acute allergic reaction occurs as if it were an ordinary reaction, are two common on-site errors.
What causes stress reactions and allergies?
Four contributing factors combine
Understanding the contributing factors helps identify where to start with prevention. The causes can generally be grouped into four categories, and several factors often combine.
1, Heterologous proteins in the vaccine itself: After the vaccine strain is propagated in specific cells, the vaccine is harvested. Due to process limitations, proteins in cell culture debris and fragments may become heterologous proteins. When introduced into pigs with the vaccine, they may trigger an antigen-antibody reaction, which is one of the direct causes of allergic reactions.
2, Local irritation caused by adjuvants: Adjuvants such as mineral oil, aluminum gel, and propolis are used to delay vaccine absorption. As foreign substances to the body, they may cause tissue edema, damage, and local swelling. This is a delayed-type hypersensitivity reaction and another factor that can trigger a group reaction.
3, Individual pigs and their condition at the time: Pigs that are ill, weak, have an elevated body temperature, are lethargic, or have a poor appetite; pigs under stress after long-distance transport; and special groups such as pregnant sows and young animals have a low tolerance and more severe reactions. Pigs that get sufficient exercise and are in good physical condition generally have milder reactions.
4, Operational and environmental factors: Injecting a vaccine directly after taking it from refrigerated storage while it is too cold can cause cold stress. Incorrect injection site or depth, excessive herding and struggling, arbitrary increases or decreases in dosage, and a noisy environment with large temperature fluctuations can all intensify stress.
Assess before immunization
Do not vaccinate these types of pigs today
The most effective way to reduce stress actually happens before vaccination. Pigs being vaccinated should appear clinically healthy. Sick pigs and pigs in other unhealthy conditions—such as being physically weak, having an elevated temperature, appearing depressed, or having a poor appetite—are not suitable for vaccination. Pigs under stress after long-distance transport should not be vaccinated yet; vaccinate them after they have returned to normal.
1, Check their demeanor: Are they lethargic, standing listlessly, or separated from the group? Check feed intake: Has it decreased or stopped completely? Take their temperature: Delay vaccination for pigs with an abnormally elevated temperature.
2, determine whether the animal is currently ill or in the incubation period of an infectious disease: pigs that are currently ill or in the incubation period must not be vaccinated. Only in special circumstances, such as an outbreak of a highly contagious disease in the herd requiring emergency vaccination, should emergency vaccination be carried out after assessment by a professional.
3, treat special groups differently: vaccination should be postponed or withheld for sick pigs, pregnant animals in poor condition, young animals, and others. Keep records and administer missed vaccinations promptly once their condition is suitable, to avoid missed vaccinations.
Before and after immunization with live vaccines, use antimicrobial drugs that inhibit the vaccine strain with caution, in accordance with the vaccine instructions. If pigs have already developed a bacterial disease, have a veterinarian assess the situation first, weighing the risks of treatment against the immune response; do not stop medication indiscriminately just to proceed with immunization.
On-site graded response
What should be done for mild, moderate, and severe reactions?
1, Mild reactions: Focus on observation and care
Symptoms include being slightly lethargic and having a reduced appetite, with no obvious symptoms. Treatment is generally not needed; natural recovery can occur in 1-2 days. Simply monitor the condition, provide plenty of drinking water, and keep the environment quiet. At this stage, do not rush to use antibiotics or fever-reducing medication. Electrolyte and multivitamin solution can be provided for free-choice drinking to relieve symptoms.
2, Moderate reactions: Promptly provide anti-allergy and symptomatic treatment
Usually appears about 15 minutes after injection: difficulty breathing, bluish discoloration of the skin over the whole body, drooling, unsteady stance, generalized weakness, and inability to rise from the ground. After assessment by a veterinarian, administer antiallergic treatment and symptomatic care; if accompanied by a marked increase in body temperature, the veterinarian will determine whether to use antipyretic medication; if accompanied by cardiac weakness and bluish skin, the veterinarian will assess whether cardiac support is appropriate. Isolate the animal on site, keep the environment quiet, and provide ample drinking water.
3, severe reactions and anaphylactic shock: provide emergency first aid immediately and contact a veterinarian
These cases are uncommon but progress extremely rapidly, often occurring within seconds to 15 minutes after injection: sudden collapse, generalized weakness, bluish skin, ataxia, difficulty breathing, drooling, pale conjunctivae, generalized muscle tremors, and altered consciousness. In severe cases, anaphylactic shock may occur, and the animal may die if rescue is not provided promptly.
(1) Notify a licensed veterinarian to come to the site immediately; farm staff should isolate the sick pig and maintain ventilation. Do not administer prescription medication by injection on your own; wait for the licensed veterinarian to arrive and provide treatment.
(2) Glucocorticoids such as dexamethasone are veterinary drugs that should be used with caution in pregnant sows and can very easily cause miscarriage. If a pregnant sow experiences immune stress, prioritize physical care and fluid replenishment. As a general rule, do not use this type of drug; if medication is essential, it must be assessed by a licensed veterinarian.
(3) Provide glucose and electrolyte-vitamin drinking water at the same time to promote metabolism.
(4) Professional procedures such as intravenous fluid replenishment must be performed by a licensed veterinarian. On-site personnel should not attempt them blindly.
Regarding fever: first determine whether it is a general fever or a high fever.
A mild, brief rise in body temperature after vaccination is usually a general reaction. Providing plenty of electrolyte and multivitamin drinking water and calmly observing the animal is usually sufficient; there is no need to immediately give an antipyretic injection. If the temperature is markedly elevated or the animal is in poor condition, promptly have a veterinarian assess it and provide symptomatic treatment as appropriate.
Guidelines for Epinephrine Use
Epinephrine hydrochloride is an emergency medicine indicated in vaccine package inserts for severe allergic reactions and anaphylactic shock. It stimulates the heart muscle, raises blood pressure, and relaxes bronchial smooth muscle to relieve shock symptoms. It is a prescription veterinary medicine, not a routine health supplement, and several guidelines for its use should be clearly understood.
(1) When to use: Only a licensed veterinarian should use it when managing an emergency involving a moderate-to-severe allergic reaction or shock. It should not be used for general reactions.
(2) Medication regimen: The dosage and frequency of administration must be determined by a licensed veterinarian based on the medicine’s instructions, the pig’s body weight, and its condition. Farm staff must not copy past practices and administer it arbitrarily.
(3) Compatibility and contraindications: Glucocorticoids pose a risk of miscarriage in pregnant sows; emergency treatment of pregnant animals should first be assessed by a veterinarian. Glucose and electrolyte-vitamin solution may also be provided in drinking water during emergency treatment. Store medicines away from light and under the specified conditions.
Emphasis: Adrenaline is a “life-saving emergency medicine” in a veterinarian’s hands. Having emergency medicines on the farm is no reason to relax the health checks and proper procedures that come first.
Prevent stress before it occurs
Prevention checklist before, during, and after immunization
1, before immunization
(1) Bring the vaccine to room temperature: After removing the vaccine, let it warm to 20-25°C in a cool environment. Do not expose it to direct sunlight or place it in a high-temperature environment, to avoid cold stress caused by low-temperature vaccines.
(2) Inspect the vaccine: Check its appearance, label, and expiry date. Do not use vaccines with loose caps, damaged vials, abnormal color, separated emulsion layers in inactivated vaccines, or vaccines that are expired or deteriorated. Transport them in an insulated container throughout, in accordance with storage requirements.
(3) Nutritional and anti-stress preparation: Around immunization, electrolytes and multivitamins, vitamin C, and similar supplements can be added to feed or drinking water to improve pigs’ ability to cope with stress; ensure complete nutrition and pay attention to mycotoxin control.
(4) Prepare a first-aid kit: Store first-aid medicines in a designated place where they are readily accessible, and check their expiration dates regularly.
2, during immunization
(1) Standardized injection: Administer vaccines by the route specified in the instructions. Inactivated vaccines require deep intramuscular injection in the neck. Use an appropriately sized needle and insert it vertically to avoid injecting into the fat layer. Use a separate needle for each pig, and promptly replace any bent needles or needles with barbs. Restrain pigs gently; avoid excessive driving, loud startling noises, and vigorous struggling to reduce mechanical stress.
( 2 ) Prepare and use immediately: Use diluted vaccines within the time limit strictly specified in the instructions. Avoid leaving them for long periods in high summer temperatures. Use them on the day they are opened; do not reuse them the next day.
3, after immunization
( 1 ) Observe closely for 15-30 minutes: Acute allergic reactions often occur during this period, so detect and treat them early. If conditions permit, extend the observation period to 30-60 minutes.
( 2 ) Provide quiet care: Reduce noise from people and livestock, provide sufficient drinking water, and create a dry, clean, quiet environment to aid recovery.
(3) Create an immunization record: document the vaccine manufacturer, production batch number, production date, packaging specifications, injection dose, and immunization time to facilitate traceability and verification of additional vaccinations.
Four judgments that are easy to get wrong
Misconception one: Immediately give an anti-fever injection and antibiotics as soon as a fever occurs. Mild fever as a general reaction often subsides on its own. Indiscriminate medication may interfere with live-vaccine immunity and mask the actual condition; symptomatic treatment is appropriate only in cases of clearly high fever or poor general condition.
Misconception two: Rush to finish and vaccinate sick and weak pigs along with the others. Vaccinating unhealthy pigs can worsen reactions or even trigger death. The correct approach is to postpone vaccination, record the pigs, and give them catch-up vaccinations after they recover.
Misconception three: Adrenaline can be injected repeatedly and in large amounts. It is a prescription medicine for emergency use and must be used under a veterinarian’s guidance. Farm staff must not arbitrarily increase the dose or inject it frequently as a routine shot.
Misconception four: Dexamethasone can be used indiscriminately for emergencies in pregnant animals. This type of medication can easily induce abortion. If a pregnant sow experiences immune stress, the treatment plan must be assessed by a licensed veterinarian.
To get back to the practical side, you only need to remember three things: before vaccinating, check whether the pigs are healthy; during vaccination, follow proper procedures and have emergency supplies ready; afterward, monitor them closely for the first half hour. Most vaccination stress can be addressed through assessment and care, while severe reactions requiring emergency treatment are rare. Checking health beforehand can reduce losses more effectively than trying to rescue animals afterward.