Lymph Nodes 101: What They Do and Why They Sometimes Swell

You're giving your dog a scratch behind the ears, grooming your horse after a ride, or checking on your goats, and then you feel it: a firm lump that wasn't there before. That moment of surprise can instantly turn into worry, especially when you realize it might be a lymph node that feels bigger than it should.

These small, bean-shaped structures are crucial parts of the immune system in all animals. They act like security checkpoints, swelling up when they're fighting off a threat. Sometimes that threat is something minor like a nearby skin infection. Other times it signals a more complex problem. It's completely normal to feel concerned when you find one, but here's what matters: an enlarged lymph node is a sign, not a diagnosis. Getting clarity is the next step.

At Rustebakke Veterinary Service, our team provides compassionate care and thorough diagnostic services to investigate changes quickly and accurately across species. Whether you're bringing in a cat, calling about your horse, or need help with your cattle or small ruminants, we're here to help. Please request an appointment whenever something doesn't seem right.

Found a Lump? Here's What to Do

A newly enlarged lymph node means your animal's immune system has noticed something and is responding. Most causes are manageable, but timing matters.

When to schedule a visit soon: If your animal is eating, drinking, and behaving normally but you've noticed a new lump, a visit within the next few days is wise.

When to seek same-day care: Multiple swollen nodes, fever, labored breathing, facial swelling, nasal discharge (especially in horses), or profound lethargy all warrant prompt attention.

Here in the Lewis Clark Valley, seasonal factors like ticks, wet conditions, and close herd contact can raise infection risk. Earlier evaluation generally helps. When you're unsure whether something is urgent, our team offers urgent pet care as well as on-site and mobile large animal care during open hours to help you figure out the right next step.

What Are Lymph Nodes and Why Do They Enlarge?

Lymph nodes are small checkpoints scattered throughout the body in all mammals. They filter fluid, house immune cells, and quietly scan for germs and abnormal cells around the clock. When they detect trouble, they swell as they ramp up their defense activity.

You can often feel enlarged nodes during routine handling. In dogs and cats, common spots include under the jaw, in front of the shoulders, the armpits, the groin, and behind the knees. In horses, the submandibular nodes (under the jaw) and retropharyngeal nodes (near the throat) are frequently checked. In cattle, sheep, and goats, nodes around the head, neck, and flank area are often palpable when enlarged.

Noticing changes during routine care is genuinely valuable. You know your animals better than anyone, and catching something early can make a real difference.

Common Causes of Enlarged Lymph Nodes by Species

Enlarged lymph nodes are a symptom rather than a diagnosis, and the underlying cause varies by species. Most cases fall into these categories: reactive responses to nearby issues, infections, inflammation, or cancer.

Dogs and Cats

In small animals, lymph node swelling commonly results from:

Infections: Dental abscesses, skin or ear infections, tick-borne illnesses like Lyme disease, leptospirosis, and regional fungal diseases.

Cancer: Lymphoma is the most common malignancy affecting lymph nodes. Canine lymphoma often presents as multiple firm, painless nodes that feel symmetrical. Feline lymphoma can appear in nodes, the chest, intestines, or other locations. Other types of cancer in pets can also spread to nearby nodes.

Other causes: Immune reactions (including vaccine responses), autoimmune diseases, and conditions like lymphedema.

Not every enlarged node is cancer. But when multiple nodes are involved or your pet seems unusually tired or is losing weight, prompt testing helps us get answers quickly.

For help locating nodes at home, guides showing where lymph nodes are located in dogs and cat lymph nodes can be useful references.

During wellness checkups at our small animal practice, we palpate lymph nodes from nose to tail and explain anything we find.

Horses

Horses develop enlarged lymph nodes for several reasons, and knowing what's common in equines helps you respond appropriately. If you're noticing lumps and bumps on your horse, lymph node swelling is one possibility worth investigating.

Strangles: This highly contagious bacterial infection caused by Streptococcus equi is one of the most common reasons for dramatically swollen lymph nodes in horses. Strangles causes the submandibular and retropharyngeal lymph nodes to become extremely enlarged and often abscess, producing thick discharge. Affected horses typically have fever, nasal discharge, difficulty swallowing, and may hold their head and neck stiffly. Understanding strangles and its complications including purpura hemorrhagica is important for horse owners, as this disease requires isolation protocols and careful management to prevent spread.

Respiratory infections: Upper respiratory infections and other bacterial or viral illnesses can cause reactive lymph node swelling, particularly around the head and throat.

Pigeon fever: This bacterial infection (Corynebacterium pseudotuberculosis) causes abscesses that can involve lymph nodes, particularly in the chest and abdomen.

Tumors: While less common than in small animals, horses can develop lymphoma and other cancers affecting the lymphatic system.

If you notice swelling under your horse's jaw, especially with fever or nasal discharge, contact us promptly. Strangles spreads quickly, and early identification protects the rest of your herd.

Regular equine wellness exams include lymph node palpation and help establish what's normal for your horse.

Cattle

In cattle, enlarged lymph nodes often signal specific diseases that have implications for herd health and, in some cases, food safety.

Bovine leukosis virus (BLV): This viral infection is widespread in cattle and can cause lymphoma. Bovine leukosis virus often goes undetected because most infected cattle show no clinical signs. However, a percentage develop lymphosarcoma, which presents as enlarged lymph nodes (often visible externally around the shoulders, flanks, or pelvis), weight loss, decreased milk production, and general decline. Testing and management programs help control spread within herds.

Tuberculosis: Though rare in many areas due to eradication programs, bovine TB causes lymph node enlargement, particularly in the head and chest.

Abscessation: Bacterial infections from injection sites, wounds, or hardware disease can cause localized lymph node swelling and abscess formation.

Actinobacillosis (wooden tongue) and actinomycosis (lumpy jaw): These bacterial infections cause swelling in the head and neck region that can involve lymph nodes.

If you notice enlarged nodes in your cattle, particularly in multiple animals or accompanied by weight loss, early veterinary evaluation helps protect your herd.

Sheep and Goats

Small ruminants have their own set of common lymph node conditions that owners should recognize.

Caseous lymphadenitis (CL): This chronic bacterial disease caused by Corynebacterium pseudotuberculosis is one of the most significant causes of enlarged lymph nodes in sheep and goats. Caseous lymphadenitis causes thick-walled abscesses in superficial lymph nodes (visible as lumps under the skin, particularly around the head, neck, and shoulders) and sometimes in internal nodes. The abscesses contain thick, greenish-white pus with a characteristic layered appearance. CL spreads through contact with abscess contents, so careful management of affected animals is essential to protect the rest of your flock or herd.

Melioidosis and other bacterial infections: Various bacteria can cause lymph node abscesses in small ruminants.

Parasites: Heavy parasite burdens can cause reactive lymph node changes, particularly mesenteric (abdominal) nodes.

Lymphoma: Though less common, sheep and goats can develop lymphatic cancers.

If you find lumps on your sheep or goats, especially ones that feel like they might contain fluid, don't lance them yourself. The contents of CL abscesses are highly contagious. Let us evaluate and manage them properly to minimize spread.

Our large animal services include herd health planning that addresses conditions like CL and helps you maintain a healthier flock.

How We Diagnose Enlarged Lymph Nodes

Diagnosis starts with a hands-on exam and conversation about what you've noticed. From there, we move to focused tests based on the species and suspected cause.

For small animals: Fine needle aspiration (sampling cells with a small needle) often gives us quick answers. We may add bloodwork, imaging, or biopsy depending on findings. Cytology can identify many infections and cancers, especially lymphoma.

For horses: Physical examination, history (including exposure to other horses), and sometimes ultrasound guide our approach. If strangles is suspected, we may recommend nasal swabs or guttural pouch evaluation. For other conditions, aspiration or biopsy helps clarify the diagnosis.

For cattle, sheep, and goats: Physical examination combined with herd history helps narrow possibilities. Blood testing can identify conditions like BLV. For abscesses, careful sampling (with appropriate biosecurity) helps confirm whether CL or other infections are involved.

Our diagnostic services team coordinates these steps efficiently and explains your options clearly, regardless of species.

Treatment Options by Condition

Treatment depends entirely on what's causing the enlargement.

Infections: Targeted antibiotics, antifungals, or supportive care based on the specific organism. For strangles in horses, treatment focuses on supportive care, hot packing abscesses to encourage drainage, and strict isolation. For CL in small ruminants, management centers on isolation, careful abscess handling, and sometimes culling decisions to protect the rest of the flock.

Cancer: In small animals, lymphoma often responds to chemotherapy, with many pets achieving remission and comfortable quality time. In large animals, cancer treatment options are more limited, but supportive care and management decisions can still maintain quality of life.

Reactive or inflammatory causes: Addressing the underlying trigger (dental disease, wounds, allergies) typically resolves the lymph node swelling.

When surgery is part of care, our surgery team focuses on gentle techniques and thorough pain management.

Monitoring and Follow-Up

Regular rechecks confirm that treatment is working and help catch changes early.

For small animals: We schedule rechecks during therapy, provide guidance on home monitoring, and adjust plans based on response.

For horses and livestock: We help you establish monitoring protocols, identify animals that need isolation or special handling, and develop herd health strategies to prevent spread of contagious conditions.

If something seems off between scheduled visits, our urgent pet care during business hours provides guidance.

Frequently Asked Questions

Are big lymph nodes always cancer?

No. Many enlarged lymph nodes result from infections or reactive responses and improve with treatment. Certain patterns (like multiple firm, painless nodes) raise suspicion for lymphoma, but testing confirms the cause.

Can I lance an abscess on my sheep or goat myself?

We strongly advise against this. If it's caseous lymphadenitis, the contents are highly contagious and will contaminate your environment, spreading the disease to other animals. Let us evaluate and manage abscesses properly.

My horse has swelling under the jaw and a fever. Should I isolate them?

Yes. Until strangles is ruled out, isolate the horse, use dedicated equipment, and contact us promptly. Strangles spreads quickly through direct contact and shared water sources.

How do I check lymph nodes on my dog or cat at home?

The easiest nodes to find are under the jaw and behind the knees. Use gentle pressure during petting and note anything that feels firm, enlarged, or different from the other side.

How Rustebakke Veterinary Service Supports You

Finding a lump can be alarming, whether it's on your cat, your horse, or your prize breeding doe. We understand that concern, and we're here to help you get answers.

What you can count on:

  • Same-day guidance during business hours for urgent concerns
  • Thorough examination with a diagnostic plan that respects your goals
  • In-house labwork, imaging, and cytology for faster answers
  • Species-appropriate care from a team experienced with small animals, horses, and livestock
  • Honest, compassionate communication at every step

Ready for Answers?

Discovering enlarged lymph nodes can be worrying, but a timely exam and focused testing turn uncertainty into options. Many causes are treatable, and even serious diagnoses can be managed with plans that protect comfort and quality of life.

Our team in Clarkston supports animals from diagnostics through treatment and follow-up, caring for small animals, providing equine veterinary care, and serving large animal needs throughout the Lewis Clark Valley.

If you've noticed a lump, please reach out to us or request an appointment so we can take a closer look and map out what comes next.