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Over the last 25 years, dedicated owners and breeders have greatly reduced the chances of producing inherited problems in their breeds by using the various health testing schemes available. For Shetland Sheepdogs this includes clinical eye examinations and hip scoring. In more recent years there have been major advances in genetic research, with the result that a number of DNA tests are now on offer and provide a useful tool in breeding programmes.
DNA testing involves sending a blood or swab sample to a specialised laboratory to determine if particular genes are present, and can establish whether or not a dog is genetically clear and has no copy of the undesirable gene(s), so can never develop, pass on, or produce the condition in any future generations.
For simple recessively inherited diseases DNA testing determines the genetic status of the dog as one of the following:-
• 'Clear' : The dog is a non-carrier of the mutant gene and therefore cannot pass the mutant gene to its progeny. The dog will never develop the disease.
• 'Carrier' : The dog carries one copy of the mutant gene and one copy of the normal gene. The dog will never develop the disease but since it carries the mutant gene, it can pass it on to its progeny with the probability of 50%.
• 'Affected' : The dog carries two copies of the mutant gene and therefore it will pass the mutant gene to all its progeny. The dog will develop the disease.
For diseases which are caused by more than one gene DNA testing can establish the level of risk of producing affected offspring – High, Medium or Low.
If both the sire and the dam are genetically clear then the puppies will all be clear and no further testing of the pups is required. The puppies will be clear by parentage. If however one of the parents is a carrier some of the puppies will also be carriers and will need to be DNA tested to check their status. The puppies will never develop the condition but could pass it on, with the result that some offspring may be carriers or, if mated to another carrier, could produce affecteds.
Collie Eye Anomaly (CEA) is an inherited eye disease where there is a lesion on the back surface of the eye, near to the optic nerve. Chorioretinal Hypoplasia (CH) is the pale patch which can be seen by an opthalmologist via a physical examination in a young dog (preferably before 7 weeks of age), however this can be very difficult to determine accurately as changes in the eye development can make the patch difficult to see – hence cases of dogs being known to “go normal” (appear to be affected at 6/7 weeks and clear a while later). In the most severe cases dogs have been known to lose their sight.
The MDR1 gene encodes P-glycoprotein, a drug transport pump that plays an important role in limiting drug absorption and distribution (particularly to the brain), as well as enhancing the excretion of many drugs used in dogs. Some dogs, including Shelties, have a mutation in the MDR1 gene, leaving them defective in their ability to limit drug absorption and distribution. These dogs also have delayed excretion of drugs that are normally transported by P-glycoprotein, making them susceptible to severe drug toxicity. The most serious adverse drug reactions involve several antiparasitic agents (ivermectin, milbemycin and related drugs), the antidiarrheal agent loperamide (Imodium), and several anti-cancer drugs (vincristine, doxorubicin, others). These drugs can produce a wide range of symptoms including seizures and even death. Knowing if your Sheltie has the MDR1 defect can help you avoid inadvertently administering the problem drugs and also to make breeding choices to ensure you do not produce puppies with the mutation.
Progressive Retinal Atrophy (CNGA1-PRA) in Shelties is clinically indistinguishable from PRA in other breeds & is characterised by visual impairment due to degeneration of the photoreceptors in the retina, eventually leading to blindness. The disease can be detected at an early stage during routine clinical examination. Over time, the disease progresses to advanced PRA in which vision loss is evident even at bright light levels.
Dermatomyositis (DMS) is an autoimmune disease that causes lesions on the bony prominences (face, tail tip, and feet). Lesions are characterized by crusting, scaling, redness, and hair loss. In severe cases, the lesions may progress to muscles and affect a dog's gait and ability to eat and drink. Onset of DMS may occur at any age, usually brought on by a trigger event such as vaccination, and lesions can come and go throughout a dog's lifetime. Fortunately DMS is a rare condition, but there have been a number of cases in the UK, and it is distressing for both dog and owner. A test for the risk factors has recently been developed which can reduce the likelihood of breeding puppies with this susceptibility.
Sourced from ESSC Website
Written By Marion Withers, Shetland Sheepdog KC Breed Health Coordinator
