Complex diseases are determined by thousands of genetic variants spread in a dog’s genome. The effects of those individual variants are typically small, but summed together they contribute to a genetic predisposition to that disease. On top of this genetic predisposition, the environment in which a dog has lived may will influence on whether the dog actually displays the symptoms of the disease or not. 

Because there are many genetic targets, and because the environment can obscure the genetic predisposition of the dog, selecting against complex diseases in dogs has only achieved modest success to date. Accurately assessing the genetic merit (the total sum of the effects of the individual genetic variants) of a dog for a complex trait requires advanced statistical tools. Such tools have been developed, and are being used very successfully in all livestock and crop species, across a wide variety of traits with different levels of genetic contribution.  These tools are called Estimated Breeding Values (EBVs).

In this talk, we are going to discuss in detail the principles of complex traits, from the difficulties in determining the effects of genotypes, to the impact of the environment. Following, we will talk about the basic methodology behind EBV calculations. Finally, we are going to discuss how EBVs are being used to reduce the prevalence of hip dysplasia in dogs registered with The Kennel Club UK. 

While tools such as EBVs are very helpful in honing in on the genetic merit of the animal and so improving the response to selection, they depend on the availability and wealth of data used in calculation. For complex diseases in dogs, this information is sourced from health testing records. As a result, progress in breeding against complex diseases in dogs can only be achieved when scientists and dog breeders work together.