How to read a health-testing certificate

When you buy a puppy or a foal, somewhere in the paperwork you are handed a set of health-testing certificates. You glance at them. You notice the numbers and the words look reassuring. You do not really know what they mean.

This is the position most buyers are in, and it should not be. Health-testing certificates are dense, technical, and written for vets and breeders rather than for the person about to spend a few thousand pounds and live with the consequences for the next ten or fifteen years.

This is a plain-English guide to the most common certificates a UK dog or sport-horse buyer will be shown — what the numbers and letters actually mean, and, just as importantly, what they do not.

One sentence first, before any of it: a health test reduces the chance of a known problem. It does not certify the future.

Hip scores (dogs)

The BVA/Kennel Club Hip Dysplasia Scheme is the one that confuses most buyers, because the scale runs the wrong way round and because the numbers mean nothing without context.

Each hip is X-rayed once the dog is at least a year old, and a vet assessor scores nine anatomical features on each hip. The two hips are added together. The lower the score, the better the hip — zero is theoretically perfect; scores into the high tens or hundreds indicate significant problems. So far, so simple.

The catch is that a hip score on its own tells you very little. What matters is how it compares to the breed mean score — the published average for that breed, calculated from every dog tested. A total of 12 is excellent for a Newfoundland and below average for a Border Collie. Responsible breeders aim to breed from animals scoring below their breed mean, and they will tell you what that mean currently is. If a breeder shows you a hip score with no reference to the breed mean, it is entirely reasonable to ask.

What it does not mean: a low hip score does not guarantee a sound dog. It means the parents had a low statistical likelihood of passing on the inherited part of hip dysplasia. Diet, weight, exercise and luck still account for the rest.

Elbow grades (dogs)

The elbow scheme is simpler. Each elbow is graded 0, 1, 2 or 3 — zero is normal, three is severe dysplastic change. The official elbow score is the higher of the two grades, not the average.

For most predisposed breeds, the advice is straightforward: 0/0 is what you want to see; grade 1 is acceptable in some breeds with careful selection; grades 2 and 3 should not be bred from. If a listing shows an elbow grade of 1 or above, it is fair to ask the breeder why they chose to breed from that animal. There are sometimes good reasons; they should be able to give one.

DNA test results (dogs)

DNA tests for inherited conditions return one of three results: Clear, Carrier, or Affected.

For a recessive condition — the most common kind tested for — the maths is more useful than it looks:

• A clear dog has no copies of the mutation. It will not develop the condition and cannot pass a copy on.
• A carrier has one copy. It will not develop the condition itself, but can pass that copy on to its offspring.
• An affected dog has two copies and will, statistically, develop the condition.

What this means in practice: two clear parents produce clear puppies, full stop. A clear-to-carrier mating produces half clear and half carrier puppies, all clinically healthy — though half the litter will themselves be carriers. A carrier-to-carrier mating, however, will on average produce a quarter of the litter as affected — and this is the mating buyers should be most alert to. A responsible breeder will not knowingly carry out a carrier-to-carrier pairing for a serious recessive condition.

You may also see the phrase hereditary clear on Kennel Club paperwork. This appears when both parents have been DNA-tested as clear by an approved lab; the puppy itself does not need to be tested because, genetically, it cannot be anything else.

Pre-purchase X-rays (horses)

Sport-horse buyers will more often encounter a pre-purchase examination (PPE) than a single scheme certificate. A standard PPE has several stages, the last of which typically includes radiographs of the joints most likely to develop problems — fetlocks, hocks, stifles, sometimes the back.

The X-rays are not pass-or-fail. The vet writes a report describing the findings — for example small bone fragments (OCD), changes to a joint surface, or features of kissing spines — and grades them by likely clinical significance. A clean set of films is reassuring. Minor findings are common in mature horses and are often clinically insignificant. Significant findings should prompt a frank conversation about workload, discipline and the horse's likely competitive life.

The single most useful thing a horse buyer can do is have the radiographs reviewed by a vet of their own choosing — not only the vet conducting the PPE — particularly if there is anything more than incidental on the films. A second pair of eyes is almost always worth the cost.

What the certificates cannot tell you

It is worth saying the obvious out loud, because it rarely is. Health tests reduce specific, known, heritable risks. They cannot tell you whether the animal will be temperamentally suited to your life. They cannot tell you how it has been raised, only how it was tested. They cannot insure you against the ordinary wear and tear of a long life.

A responsible breeder uses these certificates as one part of a wider judgement. A serious buyer should do the same.

One practical note

Every certificate you are handed when you buy an animal is worth keeping. They follow the animal for life — they matter for insurance, for any future breeding decision, and for the next vet who ever sees them. If you have nowhere obvious to put them, our free health record was designed for exactly this. A vet you share it with can see the whole set in a single scan.

Read the certificates. Then ask the questions they cannot answer.

— Rene