@PollyRoulllson
COI is so easy to find out for a pedigree dog just use kc website.
It is almost impossible to find out on cross breeds though.
Have you any evidence that cross breeds are more healthy - There are no figures on this at all.
Here:
www.instituteofcaninebiology.org/blog/health-of-purebred-vs-mixed-breed-dogs-the-data
If you track down the actual paper this article is based on, it states, "Genetic disorders differed in expression. No differences in expression of 13 genetic disorders were detected between purebred dogs and mixed-breed dogs (ie, hip dysplasia, hypo- and hyperadrenocorticism, cancers, lens luxation, and patellar luxation). Purebred dogs were more likely to have 10 genetic disorders, including dilated cardiomyopathy, elbow dysplasia, cataracts, and hypothyroidism. Mixed-breed dogs had a greater probability of ruptured cranial cruciate ligament."
And here:
www.sciencedirect.com/science/article/abs/pii/S1090023313004486
"The results of multivariable modelling indicated that longevity in crossbred dogs exceeded purebred dogs by 1.2 years (95% confidence interval 0.9–1.4; P < 0.001) and that increasing bodyweight was negatively correlated with longevity. The current findings highlight major breed differences for longevity and support the concept of hybrid vigour in dogs."
And also here:
journals.plos.org/plosone/article?id=10.1371/journal.pone.0090501
"The study identified some evidence that purebred dogs had higher disorder prevalence compared with crossbred dogs. Substantial variation was shown across breeds in their prevalence of common disorders." - a less clear conclusion than the previous papers regarding the relative health of purebred vs crossbred dogs, but nonetheless heading in the same direction.
If you understand genetics, it's obvious: if you limit a gene pool, the deleterious recessive genes that an animal will inevitably carry will have more chance of meeting other copies of that same genetic issue and expressing in the offspring (i.e. causing disease). This is before you look at the impact of inbreeding on the immune system, or the problems caused by extreme morphology (squashed faces, over-long backs etc).
And obviously, this is true of dog populations on average. There will be purebred dogs who are spectacularly healthy (the purebred I grew up with lived to be 16 or 17), even entire breeds with better health and longevity than some crossbred varieties (I'd rather own a well-bred gundog of almost any breed than a pug x frenchie).
But nonetheless, it's pretty clear that in general crossbred dogs live longer and enjoy better health than purebred dogs.
And again, I say this as someone who has purebred dogs.