Degenerative Myelopathy (DM) is a progressive disease involving the degeneration of the spinal cord, which affects 43 breeds of dog, including Rough and Smooth Collies. (source: Laboklin) The initial symptoms include ataxia (poor coordination) in the dog's rear, and dragging feet. As DM progresses the dog will eventually have difficulty standing, until it cannot walk. Sometimes the dog will develop urinary and faecal incontinence at the later stages. However, the disease is not painful. Prognosis from diagnosis is usually around 6 to 12 months.
In DM, the demyelination and axonal loss of the fibres in the spinal cord inhibit the communication of information and commands between the brain and the limbs, which causes the degenerative effect.
The disease usually affects dogs around 8 years of age (source: UFAW (Universities Federation for Animal Welfare) but can affect dogs that are younger or older.
A diagnosis of elimination is used to rule out other diseases that affect the spinal cord, using tests such as an MRI scan, myelography, and blood samples. The only method of definitive diagnosis is examination of the spinal cord during necropsy (clinical examination after death).
There is no treatment or cure for DM.
A genetic test for DM exists - which detected the gene is autosomal recessive, with incomplete penetrance. This means that dogs need two copies of the gene to be 'at risk' of expressing the disease, but even then the animal may not develop the disease.
The below chart is a theoretical breeding calculator for DM. Results in bold are results where the puppy will be 'at risk' of DM. Results that are 'around' a percentage means that each puppy has the quoted percentage chance of that result. It does not mean that EXACTLY that percentage of the litter will have the result.
RESULTS IN PRACTICE
Although it can seem like the most ethical thing to do would be to never breed from carrier dogs, erasing this portion of the gene pool would have harmful effects (please see Genetic Diversity section). Instead, ensure your breeding stock is tested, and work towards developing non carriers of the condition with subsequent generations of dogs. The UFAW recommends the following: 'Elimination of a recessive gene with incomplete penetrance from a breed is not straightforward if its prevalence is high because removing all carrier animals, that possess a copy of the gene, may significantly affect the number of animals suitable to breed from, and hence the size of the gene pool. To avoid such a problem, careful breeding of carrier animals to known healthy non-carrier individuals is recommended (Bell 2010), with slow replacement of carrier breeding animals with non-carriers over time.'
UFAW - Degenerative Myelopathy in German Shepherds
Fitzpatrick Referrals - Canine Degenerative Myelopathy