If you’ve ever walked into the barn and heard a calf breathing like a freight train, mouth open and neck stretched out, you might have come face to face with a nasty condition called calf diphtheria. It’s not just a noisy cold — it’s often caused by a bacterium called Fusobacterium necrophorum, and if not caught early, it can be deadly.

Let’s break down what it is, why it shows up, and how you can keep your calves safe.

What Is Calf Diphtheria?
Calf diphtheria (sometimes called “necrotic laryngitis”) is a serious infection that affects the mouth and throat of young cattle, usually those between 2 weeks and 2 years old, especially weaned calves or those in stressful conditions.

There are two main forms:
• Mouth form (oral diphtheria): Sores and swelling in the mouth, bad breath, trouble eating.
• Throat form (laryngeal diphtheria): Swelling in the voice box (larynx), noisy breathing, and possible suffocation. Both types are caused by Fusobacterium necrophorum, a bacterium that normally lives in a calf’s gut and manure.

But when it finds an opening — like a scrape in the mouth or throat or a calf with a compromised immune system – it will cause damage.

How Does It Start?
This infection usually pops up when calves are under stress or have minor injuries to the mouth or throat. Several conditions can predispose calves to diphtheria:
• Rough feed that scratches the mouth or throat
• Teething injuries in younger calves
• Poor ventilation or dusty, dirty bedding
• Other illnesses, like viral pneumonia, that weaken immune defenses (compromising the respiratory mucosa)
• Stressful events, such as weaning, hauling, or overcrowding

Once Fusobacterium enters damaged tissue, it produces toxins that further break  down the tissues, leading to rotten-smelling sores, swelling, and difficulty breathing.

Clinical Signs
Calves with oral diphtheria may show:
• Excessive salivation
• Swelling of the cheek or jaw
• Foul-smelling breath
• Difficulty chewing and swallowing

Laryngeal diphtheria signs are more dramatic:
• Loud, raspy, or “honking” breathing
• Open-mouth breathing and an extended neck
• Fever and depression
• Loss of appetite and rapid weight loss

Without treatment, the larynx can become obstructed, leading to suffocation and death.

Treatment: Act Fast
Diagnosis is often made based on clinical signs, so please call your veterinarian if you have a calf experiencing any of the above-listed clinical signs. Early treatment makes all the difference.

Treatment protocols:
• Antibiotics: will kill the bacteria. Reach out to your veterinarian for a prescription of an effective antibiotic against Fusobacterium necrophorum.
• Anti-inflammatories: help reduce swelling and pain.
• Supportive care: Keep calves eating and drinking — electrolytes, soft feed, warm water.

In severe cases, intratracheal injections or a tracheostomy-surgical airway (both procedures performed by a veterinarian) may be needed to save the calf’s life.

When treated early, calves often recover well. But, if the infection goes too far, the damage to the larynx can be permanent — or fatal.

Prevention: Keep Calves Clean, Dry, and Stress-Free
Prevention comes down to good calf management. Here’s what helps:

• Keep barns clean, dry, and well-ventilated
• Avoid overcrowding
• Minimize abrasive feed for younger calves
• Fix ventilation issues that lead to ammonia build-up
• Minimize stress during weaning and transport
• Promptly treat mouth/laryngeal injuries or other infections
• Provide balanced nutrition, especially vitamin A and trace minerals

While there’s no vaccine specifically for Fusobacterium necrophorum at this time, preventing the damage that allows it to invade is your best defense.

Bottom Line for Producers
Calf diphtheria is serious — but preventable. Pay attention to early signs, act quickly with treatment, and focus on solid calf-raising practices to keep this disease off your operation.

If you’ve ever lost a calf to what you thought was “just a loud cough,” take a second look. Calf diphtheria might be the hidden culprit — and with a few simple changes, you can stop it before it starts.

If you have questions about calf health, please reach out to your local Sioux Nation Ag Center veterinarians.