Without wanting to bore anybody rigid, I wrote this piece a year or two ago....
Few terms in the working-dog arena have been bandied about as much as ‘hybrid vigour’. I recently read an interesting article that stated that hybrid vigour was like communism....It only exists in theory! It made me chuckle, but is there a grain of truth in that statement?
First of all we need to look at what the Americans refer to as 'breed complementarity' and ensure that we are not confusing this with hybrid vigour. Lurcher production is one obvious example of breed complementarity where two breeds are mated together in the hope that the off-spring will display the best attributes of each parent breed. When a German shepherd is mated to a Greyhound, it is hoped that the progeny will exhibit the brains and tractability of the GSD and speed from the greyhound.
Phil Drabble, in his entertaining 'Of Pedigree Unknown' tells us that his terrier 'Mick' was a blend of working Fox terrier and Staffordshire Bull terrier. He states “Some people would have called the resulting puppies mongrels. They were certainly cross-breds, but it was a deliberate cross aimed to combine the qualities of both Bull and Fox terriers, and was by no means a street accident that conceives mongrels in the derogatory sense”.
What I would call ‘modern bushing' is another example where breed complementarity is commonly seen. In my day, back in the 80’s and 90’s (and long before that) it seemed sufficient to have a terrier or gundog breed flush out quarry to the running dogs. Now, there is a tendency to combine the best parts from terriers, spaniels and hounds for this role. While the capability of the above cross-breeds might be superior – for a given task – to the individual parent breeds, this in itself is not ‘hybrid vigour’, it is simply designer breeding, acknowledging breed complementarity.
I am no shepherd, but I understand that in the science of lamb production the line between breed complementarity and hybrid vigour is sometimes crossed. Attributes such as increased fertility, high survival rates and increased early growth rates could be a beneficial by-product of cross-breeding when one is purposefully seeking to increase wool quality or meat yield – or they could be the specific goals of breeding plans in their own right.
So, where is the scientific proof of the benefits of hybrid vigour within bog-breeding? I have only found three comprehensive, published studies with adequate sample size to give credible conclusions. One study compared Labradors, Golden Retrievers and Lab x Golden Retrievers regarding the probability of individual dogs graduating to become guide dogs. According to the various tests carried out, the success rates were 54% for Goldens, 51% for Labs and 59% for the F1 first crosses. Is the above proof of hybrid vigour or breed complementarity? I believe it is the latter.
Another study analysed genetic material from 2207 six-week-old puppies – 199 Goldens, 704 Labs, 950 Golden x Labs, 39 Golden x Golden/Labs and 315 Lab x Golden/Labs. The results revealed hybrid vigour ranging from -6% to +2.5% based on 11 separate components tested. In summary, the overall results showed no overall benefit of hybrid vigour within the cross-bred puppies.
The final study, which was on ophthalmic disorders, compared results between Labradors, Poodles and Labradoodles. The outcome revealed a 4.6% increase in the prevalence of multi-focal retinal dysplasia in Labradoodles over either parent breed, thus in this case, cross-breeding had a negative impact. Of course, other surveys might give conflicting results but I could not find absolute evidence, based on comprehensive scientific tests, that proved that the mating together of two separate dog breeds would categorically result in offspring that were healthier than either parent – every time.
Now, that does not mean that outcrossing isn't beneficial and sometimes essential to overcome severe inbreeding problems. When the co-efficient of inbreeding increases above 25%, fertility 'can' be reduced, litter sizes 'can' decrease and post-natal survival 'might' be lower. However, much of this will depend upon the overall fitness and vitality of the parents. Conversely, a mating between two unhealthy yet unrelated parents will not guarantee that the offspring will be healthy or healthier than either parent – again much of this will depend upon the state of health of the parents.
Health testing is now commonplace within pedigree dog breeds. Many breeds carry specific genetic health problems such as hip dysplasia, progressive retinal atrophy and copper toxicosis and DNA tests for these issues are readily available. However, health testing is not exhaustive, the tests will only find what they are looking for and the myriad of potential health problems that exist in most mammals – such as heart problems and cancers can still occur in dogs passing all 'breed-specific' health tests. Also, one must be aware of untrustworthy individuals who might not be completely honest about the source of the DNA sample! But.......It is certainly a step in the right direction.
Testing 'in the field' also has its merits but extremely fit dogs can be carriers of genetic faults and if two of these supreme athletes are mated together – and they happen to carry the same fault – the resulting offspring may well be affected with health problems that were not visible in either parent. When testing in the field, one must also take into account the animals age – a super-fit 4-year-old might succumb to genetic health problems from its fifth year.
Drabble, again, demonstrates the above point perfectly in the aforementioned book. He tells of an outstanding working collie that was winning numerous sheepdog trials. So impressive was the dogs performance that it became a very fashionable stud, unfortunately the dog also carried PRA. By the 1960's almost 30% of working collies were going blind by the age of 8 with some of the responsibility down to the use of that particular stud dog.
I once asked a 'Goldendoodle' owner if the dog came with a pedigree, I was immediately told, 'of course not....it isn't a pedigree breed'! I tried, in vain, to point out that the Golden retriever and the Poodle parents were likely to have pedigrees (documented ancestry) and that it would be beneficial to the designer-breed owners and breeders alike if these records were kept, if nothing else, to prevent accidental inbreeding in the future. Alas my point was completely missed! It would be a useful leap forward if we started to see accurate pedigrees within the lurcher-breeding world too.
Looking back through history, most breeds were created by mating together different breeds – not to achieve 'hybrid vigour' but to create offspring that would combine the capabilities of each parent – in essence - breed complementarity. Even so, there was, and is, no point in mating two mediocre dogs together in the hope that the offspring will be superior – the old adage of putting the best to the best and hoping for the best still rings true.
- I kept a pup back, he had a useless long haired coat on him and looked like a mini whippet when wet but was an excellent working dog and would go to ground on anything if he had the chance. Gave the other pups away , theses days they prob worth £1000
