Congenital Cerebellar Disorders in Large Animals
Arnold-Chiari Malformation in Large Animals
Arnold-Chiari malformation is a complex malformation of the caudal brainstem and cerebellum and typically consists of herniation of cerebellar tissue through the foramen magnum into the cervical spinal canal (see ). It can be associated with spina bifida, hydrocephalus, or meningomyelocele.
Courtesy of Dr. Elizabeth Parsley.
Arnold-Chiari malformation is rare in domestic animals, and the cause is unknown. In calves, it can occur with bilateral elongation and extension of the occipital lobes.
Cerebellar Hypoplasia in Large Animals
Cerebellar hypoplasia has been described in many large animal species. In utero viral infection (eg, bovine viral diarrhea, bluetongue, swine fever) during midgestation is the most common cause. Cerebellar lesions can also occur in bovine fetuses infected with Akabane or Wesselsbron viruses. Clinical or subclinical hydranencephaly and arthrogryposis can also accompany cerebellar hypoplasia.
The pathological features of cerebellar hypoplasia include destruction or loss of one or more layers of the cerebellar cortex, particularly the granule and Purkinje cell layers. Prophylactic vaccination of the dam before breeding can prevent the problem.
A hereditary cerebellar hypoplasia/dysplasia occurs in Hereford, Shorthorn, Ayrshire, and Angus calves. Cerebellar hypoplasia is present at birth and, unlike abiotrophies, is nonprogressive.
Inherited Cerebellar Disorders in Large Animals
Cerebellar Abiotrophies in Large Animals
Cerebellar abiotrophies have been reported in many species. In abiotrophies, cerebellar development begins normally, and the animal remains unaffected for a period of months or even years, before cerebellar neurons begin to die off prematurely. This progression is in contrast to cerebellar hypoplasia, in which developing cerebellar germinal cells and neurons are destroyed in utero.
In Aberdeen Angus calves, clinical signs of abiotrophy start early and are accompanied initially by seizures. In Arabian foals and Gotland ponies, the age of onset is from birth to 9 months; in Yorkshire and Large White piglets, 1–3 months; in Holstein calves, 3–8 months; and in Merino sheep, 3–6 years.
Most abiotrophies are probably inherited (eg, recessive inheritance for affected Hereford cattle and Welsh Mountain and Corriedale sheep), and an autosomal recessive mutation on the gene ECA2 has been identified in Arabian foals; however, the specific gene affected has not been confirmed.
Toxic causes of abiotrophies, including locoweed, methylmercury, and exposure to organophosphates in utero, should be ruled out. Use of trichlorfon during pregnancy can cause a congenital tremor in piglets that is due to both cerebellar hypoplasia and hypomyelination.
Hypomyelinogenesis Congenita in Large Animals
The signs of hypomyelinogenesis congenita, in which myelination is delayed throughout the CNS, are consistent with cerebellar dysfunction because of the severe head and body tremor that usually develops. In contrast to pure cerebellar dysfunction, both a persistent fine tremor at rest and a marked intention tremor are usually present. Newborn lambs, piglets, and occasionally calves are affected. Affected lambs are often called “hairy shakers.”
Hypomyelinogenesis congenita can be associated with in utero infection by viruses such as border disease virus or swine fever virus or by exposure to trichlorfon.
The condition is inherited in Saddleback and Landrace pigs and in Jersey and Shorthorn cattle. Clinical signs are usually nonprogressive or can resolve completely if myelination has only been delayed.
Also see Myelin Disorders.
Swayback in Large Animals
Swayback, or enzootic ataxia, in large animals is largely due to hypomyelinogenesis as a result of copper deficiency; however, there might be a familial predisposition.
Hypomyelinogenesis can occur in utero and cause obtundation, blindness or deafness, falling or lying prostrate, and head tremor in lambs.
In sheep, the condition can be prevented by treating affected ewes in pregnancy. Kids, piglets, and perhaps calves might also be affected.
Key Points
Cerebellar disorders can occur in utero (eg, cerebellar hypoplasia) or develop later in life (eg, cerebellar abiotrophy).
Some congenital and inherited cerebral disorders have a known environmental cause (vitamin deficiency, toxins, viral infection) or genetic cause.
A congenital or inherited malformation should be considered in any animal presenting with neurological signs beginning at a young age (< 1 year old).
For More Information
Valberg SJ. Movement disorders and cerebellar abiotrophy. Vet Clin North Am Equine Pract. 2022;38(2):409-426.
de Lahunta A, Glass E, Kent, M. de Lahunta's Veterinary Neuroanatomy and Clinical Neurology. 5th ed. Elsevier; 2021.
Mayhew IG, Mackay RJ. Large Animal Neurology. 3rd ed. Wiley-Blackwell; 2022.
Also see pet owner content regarding brain, spinal cord, and nerve disorders of horses.
