Cows get abscesses when bacteria that normally live harmlessly in their gut, mouth, or on their skin find a way into deeper tissue, usually through a wound, a damaged stomach lining, or a dirty injection site. Once inside, the cow’s immune system walls off the infection in a pocket of pus, forming an abscess. Some types are so common that roughly one in five feedlot cattle has a liver abscess by the time it reaches slaughter, costing the U.S. beef industry an estimated $256 million per year.
High-Grain Diets and Liver Abscesses
The single most common type of abscess in cattle is the liver abscess, and it’s directly tied to diet. Feedlot cattle eat high-energy, grain-heavy rations with limited roughage. When that grain is aggressively processed, it releases starch quickly in the rumen (the cow’s largest stomach compartment), which feeds acid-producing bacteria. The result is a sharp drop in rumen pH, a condition called rumen acidosis.
Repeated bouts of acidosis damage the rumen wall, creating small lesions. A bacterium called Fusobacterium necrophorum, which lives naturally in the rumen and is normally harmless, can slip through those damaged spots and enter the bloodstream. Blood from the gut drains directly to the liver through the portal vein, so the liver is the first organ the bacteria reach. Once there, they multiply and the immune system responds by walling them off, producing the characteristic pus-filled pockets found at slaughter. Research has confirmed this pathway by successfully inducing liver abscesses in both cattle and sheep through direct infusion of F. necrophorum into the portal vein.
Recent genomic work has also identified species of Bacteroides alongside F. necrophorum in severe liver abscesses, including a previously unknown species. This suggests liver abscesses involve a more complex mix of bacteria than once thought, though F. necrophorum remains the primary driver.
How Common Liver Abscesses Really Are
A 2025 analysis in the Journal of Animal Science estimated that 21.3% of U.S. beef feedlot cattle have liver abscesses at harvest. For each affected animal, the economic loss averages about $46 in reduced carcass value and condemned livers. Spread across the entire feedlot population, that works out to roughly $9.70 per animal whether it has an abscess or not.
Cattle don’t always show obvious signs of liver abscesses while alive, which is part of why the prevalence stays so high. Many cases are only discovered during processing at the packing plant.
Lumpy Jaw: Abscesses in the Bone
Actinomycosis, commonly called lumpy jaw, causes hard, bony swellings along the jawline. The bacterium responsible, Actinomyces bovis, lives naturally in the mouths of cattle. It becomes a problem when coarse or stemmy feeds, sticks, thorns, or wire puncture the lining of the mouth and push the bacterium into the underlying bone and soft tissue.
Once established, A. bovis triggers a chronic infection that destroys bone and replaces it with thick fibrous tissue and pockets of pus. The jaw becomes visibly enlarged and misshapen. Diagnosis is usually based on appearance alone, though X-rays reveal a distinctive pattern of bone destruction surrounded by new bone growth. Culturing the bacterium in the lab is difficult, so vets often rely on staining samples of the pus, which shows characteristic club-shaped rods.
Wooden Tongue: Abscesses in Soft Tissue
A related but distinct condition, wooden tongue is caused by Actinobacillus lignieresii, another bacterium that normally lives on the lining of the upper digestive tract. Like lumpy jaw, it takes hold after a puncture wound in the mouth, but it targets soft tissue rather than bone.
The hallmark is a rock-hard, swollen tongue. Affected cattle drool excessively, struggle to eat, and sometimes have a visibly enlarged tongue protruding from the mouth. Pressing on the tongue causes obvious pain. Firm or fluid-filled swelling often develops in the space between the lower jaws as well. On the inside, the tongue contains multiple nodules filled with thick, yellow-white pus. Despite its name, wooden tongue doesn’t always involve the tongue. The same bacterium can cause abscess-like masses in the neck, limbs, lungs, udder, and under the skin, and it can spread through the lymphatic system to other tissues.
Injection Site Abscesses
Every time a cow receives a vaccine or antibiotic by needle, there’s a small risk of introducing bacteria under the skin. Poor needle hygiene, reusing needles between animals, or injecting into the wrong location all increase the chance of an abscess forming at the injection site.
Beef Quality Assurance (BQA) guidelines address this directly. Injections should go into a specific triangle on the neck, not along the ribs, behind the elbow, or in the armpit. Subcutaneous injections (under the skin, at a shallow angle) cause fewer reactions than intramuscular ones. Multiple injections need to be spaced at least four inches apart, and vaccines and antibiotics should be given on opposite sides of the neck to avoid inactivating the vaccine. The highest-volume injection goes at the lowest point so any draining product doesn’t mix with other doses.
Puncture Wounds and Environmental Hazards
Abscesses can form anywhere bacteria enter through broken skin. Puncture wounds from nails, wire, thorns, or sharp objects in a pasture or pen are a straightforward cause. In the rumen, swallowed foreign objects like pieces of wire (a condition called hardware disease) can pierce the stomach wall and introduce bacteria into the abdomen or even the heart sac.
Environmental stress also plays a role. Cattle under heat or cold stress, animals dealing with illness, or calves going through the disruption of weaning and relocation are more vulnerable. Stress can cause gastrointestinal inflammation, and any inflammation in the digestive tract creates opportunities for bacteria to cross into the bloodstream. Since the bacteria that cause abscesses already live in the cow’s environment and gut, they don’t need to come from an outside source. They just need a way in.
Foot Abscesses
Cows can develop abscesses in the foot when bacteria enter through sole punctures, cracks in the hoof wall, or wounds between the toes. Wet, muddy conditions soften the hoof and make it more susceptible to damage. Once bacteria establish themselves in the sensitive tissue inside the hoof, the resulting abscess causes sudden, severe lameness. The cow typically refuses to bear weight on the affected foot, and there may be swelling above the hoof or drainage at the coronary band where the hoof meets the skin.
How the Body Forms an Abscess
The abscess itself is actually the immune system’s containment strategy. When bacteria invade tissue, white blood cells rush to the site and begin destroying both the bacteria and the surrounding damaged cells. This battle produces pus, a mixture of dead white blood cells, dead bacteria, and liquefied tissue. Over time, the body builds a fibrous capsule around the infection to prevent it from spreading further. That capsule is what gives a mature abscess its firm, walled-off feel.
This containment works well enough to keep many abscesses from becoming life-threatening, which is why cattle with liver abscesses can appear healthy. But it also means antibiotics given systemically have a hard time penetrating the capsule to reach the bacteria inside. That’s why the standard treatment for most external abscesses is physical drainage: opening the capsule so the pus can escape and the tissue can heal from the inside out.