Upper respiratory problems in cattle include diphtheria — the common name for infection/inflammation of the vocal folds of the larynx (voice box) at the back of the throat. Infection in this area is called necrotic laryngitis. Swelling from the inflammation can restrict the airway and make breathing difficult. In acute cases, the calf may die of suffocation.
Dr. Steve Hendrick of Coaldale Veterinary Clinic, a feedlot, dairy and cow-calf practice in southern Alberta, sees quite a few cases of diphtheria in cow-calf operations and in feedlots. “It’s not something we deal with every day, but it happens fairly frequently, and today there are some better ways to treat severe cases,” he says.
“We think trauma (to the throat) opens the way for the infection and inflammation, such as eating abrasive feeds,” says Hendrick. Trauma could also be caused by using a tube feeder on baby calves. “If the surface of that tube is rough (somehow damaged or was chewed on), or is forced abruptly into the throat, it may scrape or irritate the larynx.”
The infection is generally caused by pathogens in the environment. They simply need an opportunity to invade the tissues. The main ‘bug’ that causes diphtheria is Fusobacterium necrophorum, which is the same one that causes foot rot and liver abscesses and is often found in the gut and upper respiratory tract, says Hendrick.
“We suspect viruses such as IBR can play a role because they can damage the lining of the respiratory tract and open the way for bacterial infection,” he says. “In feedlots we often see diphtheria in conjunction with histophilosis.”
Histophilus somni is a bacterium that lives in the nasal passages of cattle and sometimes causes an acute, often fatal, septicemic disease, especially if it becomes complicated with other infectious agents (viruses or bacteria).
Due to swelling in the larynx (which narrows the opening), the calf has to make more effort for every breath. Hendrick says air must pass those swollen folds, so they are also constantly getting more irritated with each breath, rubbing against each other.
You may hear the calf wheezing. At first you may think it’s pneumonia because he’s struggling for breath, but if you observe the respiratory effort you can tell the difference. A calf with pneumonia has trouble pushing air out of damaged lungs, whereas a calf with diphtheria makes more effort to draw the air in through the narrowed airway.
A calf with diphtheria often drools frothy saliva because he has trouble swallowing — saliva may continually drip from his mouth. “He’s so busy trying to breathe that he can’t take time to swallow,” says Hendrick. “Extra salivation can also be due to irritation from sores in the mouth as well as the throat.”
Sometimes the infection is in the mouth and not in the throat, and that’s not as much problem for the calf because he can still breathe.
The larynx area serves as a valve, sending food down the esophagus and air down the windpipe.
“Most of the time you are just breathing; the valve only closes off the airway when you swallow,” Hendrick says. “When the calf has trouble breathing he doesn’t take time to swallow.”
If swelling in the throat closes the airway, the calf suffocates. If it is wheezing and struggling for breath, staggering from lack of oxygen, it becomes an emergency. You need to slice through the windpipe below the larynx (carefully cutting between the ribs of cartilage surrounding the windpipe with a clean, sharp knife) for the calf to breathe through.
Diphtheria is most common in calves, but older animals are sometimes affected. However, a mature animal has a larger throat and windpipe and may not have as much trouble breathing if this area becomes swollen. “The infection may still affect the larynx and in some cases may cause enough scar tissue in the vocal folds to affect the voice,” says Hendrick. Some cows lose their voice and can’t bawl as loudly anymore.
Hendrick says infection in the larynx is generally responsive to oxytetracycline — this antibiotic has good distribution throughout the body. “We also have good luck with penicillin. Some people prefer to use the newer, longer-lasting drugs because they don’t need to treat as often, but oxytet or penicillin work well.”
There are several antibiotics that can be used. Your choice may depend on your ability to catch the calf, especially if repeat treatments are needed.
Sometimes it may take as much as a month of treatment to get a calf over this problem, but there’s a way to help those persistent serious cases.
“A tracheostomy insert can bypass the swollen, irritated larynx and allow the calf to breathe through a hole in his windpipe,” says Hendrick. “Your veterinarian can place it into the calf’s windpipe below the larynx. We have great success with this, in baby calves and in feedlot calves.
There are a number of non-steroidal anti-inflammatory drugs that can also be used. It is important to discuss this with your veterinarian and treat the calf as soon as you realize he has a problem.