Blindness in Goats: 3 Common Causes
Goat pink eye isn't the only common cause of sudden vision loss.
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When it comes to herd health, keeping a watchful eye can prevent common diseases such as listeriosis, polio, and chlamydia from causing blindness in goats.
Prioritize prevention and me on the lookout for the telltale signs of these four diseases; the faster that affected goats receive treatment, the better their prognosis.
Listeriosis: A common bacteria, Listeria monocytogenes, can cause infectious disease.
Listeria bacteria thrive in cooler climates. It lives in grass, soil, unfermented silage, rotting hay, and animal feces; it also transmits through milk, urine, and nasal/eye secretions of infected animals.
The organism can cause encephalitis or swelling in the brain. It travels along the trigeminal nerve to the brain stem, where it causes clinical signs such as drooping ear, collapsed nostril, and flaccid tongue that affect one side of the face; fever, loss of appetite, depression, and blindness are also common. Listeriosis in goats progresses quickly and can cause blood poisoning, abortion, and death in as little as 24 hours after symptoms appear.
Researchers at North Carolina State University note that the fast-spreading disease often affects up to 20% of goats in a herd. Separate infected goats from the others. Listeriosis is most common in goats under three years of age and rare in older goats.
To reduce the risk of developing listeriosis in your herd, pay special attention to feeding. Ensure that all silage was properly fermented and discontinue using current feed if there is a listeriosis outbreak, advises Grace VanHoy, DVM, MS, DACVIM-LA, veterinarian and assistant professor in the College of Veterinary Medicine at The Ohio State University.
Listeriosis is a serious disease, and immediate treatment is essential.
“In some cases, aggressive antibiotic therapy may be successful, especially in mild cases,” says Kathryn Wotman, DVM, Dipl. ACVIM, assistant professor at Colorado State University College of Veterinary Medicine and Biomedical Sciences. “Mortality is high in advanced cases of listeria.”
Polio: Polioencephalomalacia, or PEM, is a nutritional disorder that can cause sudden blindness. It often results from deficient vitamin B1 (thiamine) in the diet.
“Goats and other ruminants rely exclusively on the bacteria in their rumen to make vitamin B1,” explains Grace VanHoy. “If any disturbance in the bacterial population happens, like if the rumen becomes acidic from rumen acidosis or grain overload, those bacteria die, and goats become thiamine-deficient, which is the number one cause of polio.”
The brain depends on thiamine to metabolize glucose, which is an essential energy source for the brain. With too little of the vitamin, VanHoy notes that the brain experiences an energy deficit similar to hypoglycemia that affects vision.
In addition to sudden vision loss, polio, also known as cerebrocortical necrosis or CCN, can cause other abnormal behaviors such as staring into space and loss of appetite; symptoms can progress quickly, causing seizures and death.
Preventing grain overload is one simple way to reduce the risk of polio in your goats. A diet that includes healthy amounts of forage encourages activity in the rumen, which stimulates thiamine for goats.
VanHoy notes that CORID, the medication used to treat coccidiosis, can also cause thiamine deficiencies. The drug has a molecule that competes with thiamine and can lead to polio. Give thiamine injections alongside CORID to avoid issues.
Bottle-fed kids are also at risk of developing polio.
“Babies don’t have working rumens that produce thiamine…[and] a lot of milk replacers don’t have vitamin B1 in them,” VanHoy explains.
If you have to bottle-raise a kid, she suggests choosing a milk replacer with added thiamine or offering thiamine pastes or gels as a supplement, adding, “The sooner you can transition them to solids, the better, because those rumen microbes will start ruminating and take over the production of thiamine.”
Goats that develop polio need immediate medical attention. Injectable thiamine can reverse the symptoms. It might take a few weeks to restore vision, but, VanHoy adds, most goats do regain their sight.
Chlamydia: The species of Chlamydia bacteria that causes conjunctivitis is different than the species that causes abortion.
Flies transmit the bacteria that causes chlamydia in goats; it sticks to their feet and transfers to goats when the flies land on their faces and eat their eye secretions, causing a painful inflammatory infection that can cause vision loss.
“[It] can cause corneal ulcers, corneal vascularization, as well as uveitis, which is inflammation inside the eye secondary to the corneal disease,” says Wotman. “Goats typically show signs of ocular pain, including blepharospasm (squinting) and epiphora (tearing) from the affected eye.”
Chlamydia also causes ocular inflammation and cloudiness on the eye’s surface; the cloudiness may become so severe that it causes temporary blindness in goats.
A topical antibiotic ointment plus an antibiotic injection are often enough to clear up the infection and, if caught in the earliest stages, allowing goats to regain their vision. VanHoy warns that treatment is time-consuming because the ointment needs to be applied at least three times per day. If multiple goats in the herd are affected, treatment becomes arduous. For goats outside, using an eye patch can help ease the pain associated with bright light until the bacteria clear. Goats that receive immediate treatment often recover within seven to 10 days.
If left untreated, the bacteria will create corneal scars that permanently affect vision or a severe infection that can force the affected eye’s removal.
“Separate goats showing signs of ocular infections, and wear gloves and change clothes when the same person is handling an affected goat as well as unaffected goats,” advises Wotman. “Generally good hygiene in the barn as well as minimizing stress, things that generally promote a healthy immune system, may reduce risk of infection.”
Chlamydia is more common in enclosed areas like barns, with poor ventilation. Goats with access to open pasture are less likely to develop the disease. It’s also more common in summer when heat and humidity create the perfect environment for the bacteria to flourish. Fly control is essential in the summer, especially if you must house goats in enclosed areas, VanHoy says.
There is no guaranteed way to prevent diseases that can cause blindness in goats. Performing daily inspections and monitoring your animals for changes in appearance or behavior could help you identify issues early and administer treatment to protect their eyesight.
Originally published in the 2021 special issue of Goat Journal — Goat Health from Head to Hoof Vol. 2 — and regularly vetted for accuracy.