The most common brain diseases that I find in adult goats are polioencephalomalacia (PEM) and listeriosis. PEM can inflict
animals at any age. In cattle, it usually is associated with high-concentrate diets, sudden dietary changes or high molasses
or sulfur content in the diet. My experience with goats, however, is that these predisposing factors usually are not present,
and the condition appears stress-induced (weaning, housing changes, new-animal introductions, bad weather). Signs associated
with PEM are central blindness, depression, incoordination, head pressing, recumbency, opisthotonus, seizures, vocalizations
and/or dorsomedial strabismus.
PEM and lead toxicity can cause central blindness, and lead toxicity cases can respond transiently to thiamine treatment,
so lead toxicity should be a differential diagnosis for PEM. Definitive diagnosis of PEM requires measurement of RBC enzymes
that is not readily available in practice, so a diagnosis of PEM usually is made by response to treatment with thiamine. PEM
can be treated with thiamine (5 mg/lb SQ, TID to QID). If caught early, the prognosis is good. If no response to treatment
is seen in one or two weeks, the animal likely will have permanent deficits. Supportive care is important if animals cannot
eat or drink. Transfaunation of rumen contents from a normal ruminant might help if GI disease is severe. Control of seizures
usually can be accomplished with Valium, but phenobarbitol occasionally is needed.
Listeriosis affects goats more often than cattle and sheep. It commonly appears in winter and early spring but can occur any
time during the year. Any damage to the oral mucosa (erupting teeth, introduction of hard feeds or browse) can predispose
to listeriosis. It occurs in animals grazing close to the ground and eating wet, moldy hay. It is not commonly associated
with silage feeding. Listeriosis in goats is characterized by depression and cranial nerve deficits. Circling is frequently
seen, but listeriosis should be considered with any cranial nerve deficit, especially if multiple, asymmetric deficits exist,
even if circling is not present. Progression of the disease can be quick, with many animals found recumbent.
The most likely differential diagnosis for listeriosis is brain and/or spinal cord disease due to migration of Parelaphostrongylus
tenuis (meningeal worm), which is common in some areas of the country. Confirmation of a diagnosis of listeriosis and meningeal worm infestation can
be difficult. With listeriosis, a CSF tap shows elevations in protein and mononuclear cells, but this also can be observed
with other diseases. CSF might also be normal in a small percentage of cases, especially if taken from the lumbosacral space.
P. tenuis migration sometimes causes increased numbers of eosinophils in CSF.
Listeria can be difficult to culture, and a negative CSF culture does not rule out listeriosis. If the clinical signs are
consistent with listeriosis, antimicrobial therapy is indicated. Tetracyclines and penicillins are effective if administered
early. Some cases seem to respond to one but not both antibiotics, and predicting which one will work is difficult. If no
response is seen to either antibiotic within 48 hours, the drug therapy should be changed.
Because listeriosis can occur in multiple animals on a farm, historical response to therapy is important to track. Anti-inflammatory
therapy (non-steroidal or steroidal) and supportive care is crucial. These animals might be unable to eat or drink and can
become acidotic due to excessive saliva loss, so fluid and nutritional support are indicated.
Goats are susceptible to tetanus. This disease should be suspected in non-vaccinated animals showing signs of lameness or
stiffness. Clinical signs and treatment are similar to other species.
Scrapie and rabies
No discussion of neurologic diseases of small ruminants would be complete without mentioning scrapie and rabies. Scrapie is
a transmissible spongiform encephalopathy more common in sheep, but it does manifest in goats. It is transmitted horizontally
and vertically. Host genetics and stain of the infectious agent determine whether an animal will develop the disease. The
genetics of susceptibility are well defined in sheep but not in goats. The clinical signs are intense pruritus, ataxia and
wasting. There is no treatment for scrapie. The only antemortem test is immunohistochemistry of lymphoid tissue from the nictitating
membrane or rectal mucosal biopsy.
Rabies in goats can present with a variety of clinical signs. Sometimes the dumb form occurs where animals are depressed and
progress to recumbency. Others are more aggressive, attacking people and animals and sometimes becoming sexually excited.
Rabies can be prevented via vaccination.
Bacterial meningitis, brain abscesses, otitis, toxicosis and injuries that occur in other livestock species can occur in goats.
The clinical signs, diagnosis and treatment also are similar to other livestock species. Organisms most often causing meningitis
are E. coli, Pasteruella spp., and Mycoplasma spp. and also are implicated in otitis media. Brain abscesses most often are caused by Actimomyces spp. Common toxicities include rhododendron (azalea), organophosphate, and lead toxicity. Salt toxicity/water deprivation also
Though much less common than bacterial meningitis/otitis, goat kids also might have neurologic disease due to enxootic ataxia
and spinal abscesses, and the neurologic form of Caprine arthritis encephalitis virus (CAE). Enzootic ataxia, also called
swayback, is caused by primary or secondary copper deficiency in does. Signs of weakness and ataxia are seen within a few
weeks of birth. Treatment usually is unsuccessful because damage to neurologic tissues usually is irreversible. Spinal abscesses
usually present as acute spinal paresis/paralysis when the vertebral body fractures through the infection site. CAE most commonly
presents as arthritis in adult goats, but can cause ataxia/paresis/paralysis in goat kids age 1 month to 4 months.
Dr. Navarre works as an extension veterinarian with Louisiana State University's Department of Veterinary Science.