Eye infections in pigs are common and usually treatable, but the right approach depends on what’s causing the problem. Most cases involve conjunctivitis, the swollen, red, weepy eyes you’ve probably already noticed in your herd. Treatment typically combines cleaning the eye, addressing the underlying cause (bacterial, viral, or environmental), and fixing barn conditions that may have triggered the infection in the first place.
What Causes Eye Infections in Pigs
Conjunctivitis in pigs usually falls into one of three categories: bacterial or viral infection, environmental irritation, or a structural eyelid problem. Knowing which one you’re dealing with shapes how you treat it.
The most common infectious agents behind swine conjunctivitis are Mycoplasma hyorhinis, Chlamydia suis, and Glässer’s disease bacteria. Viral causes include porcine cytomegalovirus and swine influenza. In many cases, the eye infection is actually a secondary symptom of a respiratory or systemic illness rather than a standalone problem. If several pigs develop red, watery eyes around the same time that coughing or nasal discharge appears in the barn, the eyes are likely reacting to a broader infection moving through the herd.
Environmental irritants are the other major culprit. Ammonia from urine and manure buildup is the classic trigger. Confinement swine barns typically run 5 to 18 ppm of ammonia, but once levels climb above 50 ppm, rates of eye inflammation and airway irritation rise sharply. Dust and poor ventilation compound the problem. Sometimes a foreign body, a piece of straw or bedding, gets lodged under the eyelid and causes localized irritation that looks like infection.
Signs to Watch For
A pig with conjunctivitis will have red, swollen eyelids and watery or mucus-like discharge. The eye may be partially or fully shut, and the pig might rub its face against walls or pen fixtures. In mild cases, only one eye is affected. When both eyes are involved across multiple animals, suspect either an airborne irritant or an infectious agent spreading through the group.
Pay attention to what else is happening with the pig. Because swine conjunctivitis is frequently a secondary symptom of respiratory disease, look for coughing, sneezing, lethargy, or reduced appetite. Mycoplasma hyorhinis, one of the most common bacteria behind pig eye infections, also causes pneumonia and ear infections. If a pig with red eyes is also off feed, running a fever, or showing breathing difficulty, the eye problem is part of something bigger that needs systemic treatment, not just eye care.
Cleaning the Eye
Before applying any medication, you need to flush debris and discharge from the affected eye. Use a store-bought sterile saline eyewash rather than a homemade solution. Homemade saline carries a real risk of introducing additional bacteria, no matter how careful you are with preparation.
If sterile saline isn’t immediately available, you can prepare a rinse by boiling tap water for three to five minutes and letting it cool to lukewarm. This won’t be as reliable as a commercial product, but it’s better than using unboiled water. Gently restrain the pig (a second person helps enormously), hold the eyelids open, and flush the eye to clear crusted discharge and any visible debris. Repeat this cleaning once or twice a day until the eye starts to improve.
Antibiotic Treatment for Bacterial Infections
When the infection is bacterial, injectable oxytetracycline is one of the most widely used treatments in swine. It’s administered as an intramuscular injection in the neck at 3 to 5 mg per pound of body weight per day. A long-acting formulation at 9 mg per pound can be given as a single dose when daily re-treatment isn’t practical, which is often the case with pigs that don’t tolerate repeated restraint well. Treatment should continue for 24 to 48 hours after symptoms improve but shouldn’t exceed four consecutive days.
Your veterinarian may also recommend topical antibiotic eye ointments applied directly to the affected eye. These are especially useful for localized infections that haven’t spread systemically. The ointment is squeezed along the inside of the lower eyelid after flushing, and the pig’s blinking distributes it across the eye surface.
For herds where Chlamydia suis is identified as the cause, tetracycline-class antibiotics are the standard approach since chlamydial organisms respond well to this drug family. If Glässer’s disease bacteria are involved, your vet may choose a different antibiotic based on sensitivity testing.
Withdrawal Times for Meat Animals
If you’re raising pigs for slaughter, withdrawal periods are critical. Injectable oxytetracycline (the long-acting formulation) carries a 28-day preslaughter withdrawal. Other common injectables have their own timelines: penicillin requires 7 days, lincomycin requires 2 days, and tylosin requires 14 days. Always check the product label, as withdrawal times can vary between formulations of the same drug. Gentamicin has one of the longest withdrawals at 40 days, making it a poor first choice for finishing pigs close to market weight.
Entropion: When the Problem Is Structural
Overweight pot-bellied pigs and some adult commercial pigs develop a condition called entropion, where fat deposits around the eye socket cause the eyelid to roll inward. The eyelashes and lid skin then rub constantly against the eye surface, causing chronic irritation, tearing, and secondary infection. These pigs often become more aggressive because they can’t see well.
Antibiotics and eye flushing won’t fix entropion. The pig needs a surgical correction to remove the fat pad and realign the eyelid. This is a relatively straightforward veterinary procedure, but it does require sedation. If you have a pig with chronically weepy, irritated eyes that never fully clear up with treatment, entropion is worth investigating, especially if the pig is overweight.
Fixing the Barn Environment
Treating individual pigs is only half the solution if your barn conditions are driving the infections. Ammonia management is the single most impactful change you can make. Increase ventilation, clean manure more frequently, and check ammonia levels if you have access to a detector. Your nose can pick up ammonia around 25 ppm, so if you can smell it strongly when you enter the barn, your pigs are breathing it constantly at levels that irritate their eyes and airways.
Dust reduction matters too. Wet-feeding systems produce less airborne dust than dry feed. If you use dry feed, consider adding a small amount of vegetable oil to reduce dust at the feeder. Bedding choices also play a role: finely chopped straw generates more airborne particles than longer-cut material or alternative bedding types.
Controlling Flies and Preventing Spread
Flies are a major vector for spreading eye infections between pigs. They feed on eye discharge from an infected animal and carry the bacteria directly to the next one. Controlling fly populations in and around your pig housing reduces transmission significantly.
A multi-layered approach works best. Keep manure cleaned up promptly, since fly larvae develop in fresh dung. Insecticide sprays using organophosphate or permethrin-based products can be applied to pen surfaces and around doorways. Feed-through larvicides dosed to the animal’s weight can reduce fly emergence from manure, but they need to be consumed consistently every day throughout fly season to be effective. If your pigs have outdoor access, providing shade reduces their exposure to flies during peak daytime hours and limits the sun glare that worsens eye pain in infected animals.
When one pig in a group pen develops an eye infection, isolate it if possible. Shared feeding and watering areas allow nose-to-nose contact that spreads infectious agents quickly. Treating the affected pig while leaving it in a group pen often leads to reinfection or spread to penmates.
When Eye Infections Signal a Bigger Problem
A single pig with one mildly irritated eye that responds to flushing and a clean environment probably doesn’t need aggressive intervention. But when eye infections show up across multiple pigs simultaneously, it points to either an environmental trigger affecting the whole barn or an infectious disease moving through the herd. Swine influenza, cytomegalovirus, and Mycoplasma infections all cause conjunctivitis as part of a broader illness, and treating only the eyes while missing the underlying disease means you’ll keep seeing new cases.
Pigs whose eye infections don’t improve within three to four days of treatment, or that develop cloudiness or ulceration of the eye surface, need veterinary evaluation. Corneal damage can become permanent if left untreated, and a clouded or ruptured eye affects the pig’s welfare and, in commercial settings, its ability to find feed and water efficiently.