The West of England Collie Society has always taken a keen interest in health matters, for many years holding an annual eye testing session in conjunction with one of its shows,
whilst the ‘Round Up’, edited by Mrs Hazel Hunt, which became freely available to all members in 1979, has, over the years, highlighted many topics of interest to the exhibitor/breeder.

Many herding breed dogs (the most commonly affected in the UK are: All breeds of Collie, Shetland Sheepdog, GSD and, Australian Shepherd dogs - including cross breeds) have a genetic predisposition to adverse drug reactions involving over a dozen different drugs. 

The most serious adverse drug reactions involve several antiparasitic agents, Ivermectin, Milbemycin (and related drugs), the antidiarrheal agent Loperamide (Imodium)and several anticancer drugs (Vincristine, andDoxorubicin, plus several others). These drug sensitivities result from a mutation in the multidrug resistance gene (MDR1 gene). 

A test distinguishes between clear, carrier and affected dogs. Clear dogs have no copies of the mutant gene responsible for the condition and will neither develop the condition nor pass the gene on to their offspring. Carrier dogs have one copy of the normal gene and one copy of the mutant gene, they will not develop the condition, but will pass a mutant gene on to approximately half of their offspring. Affected dogs have two copies of the mutant gene that causes the condition, and therefore, will react adversely to certain drugs.

When considering the use of macrocyclic lactones such as ivermectin or moxidectin in dogs, vets have followed the adage, “white feet, don’t treat.” This refers to the known sensitivity of Scotch collies (both rough and smooth) to neurotoxicity when administered these drugs at higher than label doses. But the adage has also been applied to many other herding breeds and has prevented vets from using these drugs in situations where they would have been ideal. The neurotoxicity was attributed to a leaky “blood-brain barrier” in susceptible dogs. Recent developments in the molecular mechanisms of this phenomenon have opened a new frontier in the area of pharmacogenetics — drug disposition determined by the animal’s genotype. So “white feet, don’t treat” is no longer the practice standard; now it is “white feet, test to see if you can treat.”

Recognizing that the collies and other herding breeds that were sensitive to ivermectin were similar to the mdr knockout mice, Dr. Katrina Mealey at Washington State University, College of Veterinary Medicine, demonstrated that a deletion mutation of the mdr gene was present in ivermectin-sensitive collies.

The current list of drugs (as at December 2012) that cause sensitivity to dogs with the MDR1 mutation is as below,  but please refer to LABOKLIN for up to date information as new drugs are often added.

There are many other drugs that have been shown to be pumped by human P-glycoprotein (the protein encoded by the MDR1 gene), but data is not yet available with regard to their effect in dogs with the MDR1 mutation. Please also refer to a list maintained by Washington State University HERE






More usually referred to as CEA is a non-progressive congenital, present at birth, hereditary abnormality of the eye which affects members of the wider Collie family. Originally thought to be a simple recessive its mode of inheritance no longer appears to be quite so simple and it is probable that its more severe expressions involve additional gene mutations that have yet to be identified.

Usually bilateral, affecting both eyes, in its milder forms it is no more than a slight lack of pigment to, or thinning of the optic disc which does not appear to affect the sight in any way. In its more severe forms, which thankfully represent less than 9% of the total Rough Collie population, it can manifest itself as Colobomas of varying sizes and/or partially or wholly detached retina, this latter condition producing blindness.

Being a congenital condition CEA can be detected at an early age, the only method of discovering which if any puppies are clear, or only mildly affected by CEA, is to have the whole litter eye screened for the condition, by a BVA listed ophthalmologist, at the age of 6 to 7 weeks.

Many puppies diagnosed age 6-12 weeks as ‘mildly affected’ will appear to be completely free of CEA if tested when older, this is often referred to as CEA ‘go-normal’. CEA is inherited as an autosomal recessive trait and both parents must carry at least one copy of the defective gene for the offspring to be affected.






Commonly referred to by its initials, PRA, it is a progressive inherited eye abnormality, which causes eventual blindness. 

Generalised Progressive Retinal Atrophy or GPRA is of early onset and typically apparent by the time a puppy reaches six weeks of age. Current opinion is that this condition does not affect Rough Collies in their country of origin, although it is known to affect Collies in North America, which explains why the Collie Club of America’s Health Foundation funded the research into its genetic inheritance which has since established a DNA test for the condition. This has little relevance to breeders in the United Kingdom or Europe unless they intend incorporating North American blood lines into their breeding programme.

Central Progressive Retinal Atrophy or CPRA is in many ways a more insidious condition, which can not be detected until it manifests itself sometime after the first year of life, and frequently not until quite late in life explaining why breeders are urged to submit their breeding stock for regular eye screening. The condition’s development is also somewhat unpredictable often taking many years before serious loss of sight is experienced if ever. It is also considered that improvements in canine nutrition may have been largely responsible for today’s low incidence of the condition as it is known that Vitamin E deficiency can affect the eventual outcome and most modern feeds use Vitamin E as a preservative.

The possibility of a DNA test being discovered remains slim as the actual mode of inheritance is still not fully 
understood, and with the number of confirmed cases being less than 0•25% of all dogs tested under the 
BVA/KC Eye Scheme there is little encouragement for further research. 

No cases of PRA have been reported in British Collies in several years - Optigen now offers a DNA test for the early onset form of Generalised PRA (RCD2) which affects American Rough and Smooth Collies and it is recommended that all British/American/Canadian bloodlines are tested to prevent this eye problem from entering the British gene pool.

Kennel Club Announcement - March 2014

Recording CEA and prcd-PRA DNA tests
The Kennel Club would wish to clarify the position with regard to the recording of DNA test results for both prcd-PRA and CEA/CH.

Both these DNA tests carry patents in the UK and most other European countries. The patents are owned by Cornell University in the US, and are licensed exclusively to OptiGen worldwide. They also have non-exclusive licensing of the CL test (for Border Collies) in Europe (and exclusive use of this patent in the USA). It is important to note therefore that the KC will only officially record the DNA results for these diseases if they have been tested by OptiGen (or Genetic Technologies in Australia who have a licence to perform the tests).

Part of the patent includes the advertisement and recording of results and therefore whilst this patent is still in force, the Kennel Club will only be publishing the outcome of Optigen tests. The position the KC has taken stems purely from legal ramifications and has no reason to question the quality and reliability of tests offered by other labs. For clarification, only results of prcd-PRA or CEA/CH DNA tests issued by Optigen will be recorded by the KC, and these results will appear on registration certificates, in the BRS and online via Mate Select.

However, we are aware that other laboratories such as Laboklin and Idexx have made arrangements with Optigen so that if any of their clients want either prcd-PRA or CEA/CH results recorded, these labs will send the DNA to Optigen and they will issue a result / certificate back to laboratory.



by Pat Hutchinson



Please contact our Collie Health Coordinator, Ros MacDonald, 01275 790451, for more information