Bovine Progressive Degenerative Myeloencephalopathy

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Diseases and conditions image EquiMed

Also known as

Weaver syndrome


This genetic condition occurs in Brown Swiss cattle (both male and female animals) and was occasionally seen in Canada in the 1970s and associated with importation of cattle from Europe.

The first documented case of bovine progressive degenerative myeloencephalopathy in Canada was seen in 1970 when a 15-month-old purebred Brown Swiss heifer was examined by a veterinarian because of posterior paresis (hind leg weakness) and ataxia (lack of coordination).

After euthanizing the heifer, examination of her brain and spinal cord tissues under a microscope showed evidence of mild degenerative myeloencephalopathy (inflammation of both the brain and spinal cord).

The defect in the spinal cord causes affected animals have difficulty getting up and walking. Some of them may “goose-step” or wobble as they try to walk.

This condition is not present at birth (the newborn calf seems normal), but starts to be noticeable at 4 to 6 months of age, sometimes younger. After starting in the hind limbs it progresses insidiously and remorselessly during the next few months, with progressive muscular weakness and paralysis.

The animal becomes more wobbly and uncoordinated. Usually by the time the animal is of breeding age (12 to 14 months) it becomea so weak that it will be down and can’t get up. It affects the front limbs last.

This condition is uncommon today because during the past 20 years or so, with genetic testing, this disease has nearly been eradicated. There has not been a clinical case in North America for a long time.


  • Hind leg weakness first appears about 5 to 6 months of age
  • Weaving wobbly gait
  • Progressive lack of coordination
  • Unable to get up - usually by 12 to 18 months of age


This is a spinal cord disease, causing spinal cord damage, and is an autosomal recessive disease which means that two copies of an abnormal gene must be present in order for the problem to develop. It only appears when both the sire and dam of the calf carry the recessive gene and it is doubled up in the offspring.


The abnormal gene has been identified and a genetic test is available. Carriers of the gene can be identified, and if a breeder doesn’t mate two carrier animals, this defect will never appear in the calves.

A genetic test is required before a Brown Swiss calf can be registered, and all Brown Swiss bulls are screened for BPDME before their semen can be used. This ensures that no more “weaver” calves will be produced.


There is no treatment, so humane euthanasia is the only option. There is no test for this disease in a live animal. If you suspect a case, you can’t do a blood test or specific diagnostic test that would show that this animal has weaver syndrome. You can exclude some of the other possible causes of weakness—other diseases that might look like it, or a broken back or spinal abscess, meningitis, etc. but there is no definitive diagnostic test for weaver syndrome. The proof can only come from pathology at necropsy, looking at the spinal cord after the animal is dead.

The good thing about genetic diseases is that research has been able to identify the genes that cause many of them, and with testing we can detect the animals that possess the defective genes, and not select them for breeding.

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EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.