by Keith Erlandson| Hips & Eyes by Keith Erlandson |
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-2- PRA is a dreadful affliction which usually causes total blindness. There are two phases, generalised and central, both of which can affect labradors but the working English Springer appears to be unaffected. Generalised is the most dangerous phase as it is recessive, ie, two clinically clear parents can carry a recessive gene and affect a proportion of their offspring as clinical cases and unaffected carriers but according to the latest information, carriers can be isolated by blood test at an early age. Central PRA seems dominent whereby only clinically affected dogs can pass it on, which happens in the case of the Border collie, so if clear parents are bred from, the pogeny should be unaffected. The acclaimed geneticist Dr. Malcolm Willis considers Generalised PRA to be more dangerous than hip dysplasia as a breeding programme can improve hips but there is no such thing as degrees of PRA. It is either present or it is not, whereas perfect hips are largely hypothetical but not completely unknown. Hip testing many years ago was arbitrary. There were only three results, pass, fail or breeders'letter, the latter signifying quite good but less than perfect hips. The current system of hip scoring seems to allow more latitude. Nine divisions on each hip are scored individually, to give at worst, a total of 53. Eight divisions can attract a maximum of six points each and the ninth, five. The first mentioned division is the Norberg angle which is not part of the skeletal structure but a measurement. Next is subluxation, arguably the most significant as it relates to joint fit, how well bedded into the socket is the ball of the femur or how shallow. Then comes the cranial acetabular edge. The sum total of these divisions gives an indication of the degree of a dog's hip dysplasia or more hopefully, the lack of it. The last two items out of the nine, femoral head/neck exostosis and femoral head recountering, relate to extra bone growth, a feature which may or may not, cause arthritis later in life. My own vet says, "Let's face it, a 0/0 score is a fluke, whereas should a dog attract only one point on each division, to a total of 18, the hips would be almost perfect, which would bring it well over the mean score of 12.5 and the rule of thumb advocated seems to be to breed only from dogs with a mean score or under. However, should a dog score 6/6 on subluxation it would be dysplastic but still within the mean score, so where a hip scores and how heavily, is of the greatest significance." With the passage of time it has been demonstrated that with all breeds predisposed to HD, the situation can be improved by breeding from parents with 'good' hip scores but it is not infallible and it is possible for parents with good hips to produce the occasional dysplastic pup and conversely, parents with imperfect hips can produce better scoring progeny than themselves, so there are ambiguities aplenty. In his mamoth tome, The Genetics of the Dog, a standard work for all veterinary students, Dr. Malcolm Willis cautions against 'breeding for hips' with disregard for other essential qualities, rightly pointing out that serious eye problems and bad temperament can be far more damaging in a bloodline. Whilst recognising that due regard should be paid to hip testing schemes, it would appear that Dr. Willis warns against sacrificing pragmatism on the altar or pedantry. Perfect hips and a dull brain never will win the Retriever Championship. Dr. Willis's own breed is the German shepherd. Several years ago he heard of an animal which had scored 0/0. He had to see this wonderous animal. It was such an awful specimen that no informed breeder would ever have bred from it. |
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