What is hybrid vigour, and what do we mean when we say a dog has it?

Hybrid dog types – also known as designer dogs, cross-breeds or simply mutts (like the Cavapoo, Cavachon and Chorkie) are becoming better known and more and more popular every year in the UK, and dogs of hybrid types are in great demand amongst many different types of owners.

If you ask any given dog lover what they like about any given dog breed or type, they might be able to provide you with a detailed list of answers off the top of their heads or really struggle to say anything other than “I don’t know, I just like them.” But when it comes to common consensus on the plus points of hybrid dog types above pedigrees, one of the most widely agreed bonuses of choosing is hybrid is that they benefit from hybrid vigour.

A lot is said about hybrid vigour and the advantages that this confers upon hybrid dog types in terms of their health, and the basis of hybrid vigour and its broad evolutionary genetic advantages are scientific facts, not speculation.

However, not all dog owners and prospective hybrid dog buyers really understand what is meant by hybrid vigour, why it is a good thing, and also, its limitations and variables – and so this article is designed to provide a basic explanation of hybrid vigour and what it means for dogs. Read on to learn more.

What is hybrid vigour?

Hybrid vigour is a scientific term that is generally explained as “the tendency of a cross-bred animal or plant to have superior qualities to that of either parent.”

Breaking that down a little is important as the meaning of even some of the individual words used within that description require clarification for context.

What is a hybrid?

A hybrid means a cross breed, or a mixture of two genetically different individuals. In hybrid dog types, we call them hybrids because they’re a cross – a hybrid – of two different pedigree breeds. Dogs of individual pedigree dog breeds are by nature not very genetically diverse from each other within the context of the species of the whole, but diversity in this context is a sliding scale.

Some breeds have larger populations and so, more genetic diversity within the breed than others, but the mixture of two unrelated breeds will always be more genetically diverse than can be found wholly within any one pedigree breed.

What is vigour?

Vigour in this context, means robustness, health, fitness for life and essentially, any traits that help an animal to survive in their natural environment; their level of vigour is their level of evolutionary advantage.

Many people think that hybrid vigour just means health, but it doesn’t – it can also refer to other traits that help an animal to cope, evolve, or survive – such as humans evolving with opposable thumbs!

Health and being fit for life are inextricably linked, and hybrid vigour is widely used generally to talk about hybrid dog health and its theoretical advantages more than any other trait.

What do we mean by “superior qualities” in this context?

When we talk about those “superior qualities” this is again meant in a scientific and evolutionary context only. It does not refer to traits that we as humans might (or might not) find “superior” in our own choice of dog, which means that it doesn’t mean things like a low shedding coat or what most people think of as good looks.

Put simply, a dog with a high level of genetic diversity because they’re bred from two genetically diverse parents (from two different breeds) has superior evolutionary qualities to a pedigree or even to a non-pedigree bred from the same or closely related breeds or individual parent dogs.

Are all hybrid dog types equally genetically diverse and so, subject to the same degree of hybrid vigour advantages?

Just as the level of genetic diversity in a pedigree breed’s gene pool can vary from breed to breed as mentioned above, so too can this be the case for hybrids.

For instance, a hybrid dog type like the Cockapoo (bred by crossing a poodle and a cocker spaniel) will be more genetically diverse (and so have a higher level of hybrid vigour) than a Sprocker (bred by crossing a springer spaniel and a cocker spaniel).

This is because the poodle and cocker spaniel breeds are significantly more genetically different to each other (in relative terms within the canine species) than the cocker and springer breeds, which are unique breeds in their own right but close relatives in pedigree terms within the remit of the species.

Can you work out the level of hybrid vigour any given hybrid dog has?

Possibly. Every pedigree dog breed has a statistic associated with it known as the “coefficient of inbreeding.” This is expressed as a percentage figure, and it refers to the likelihood that a dog has inherited two copies of the same gene variant, one from each parent – as opposed to just one, as only one parent possessed it and passed it on.

This information can be useful for pedigree dog breeders to work out the potential risks of mating two dogs from within the same breed when it comes to the future hereditary health of their litter.

The higher this percentage number is across the board for an individual breed as a whole, the lower the level of genetic diversity within the breed.

If you’re looking at a hybrid dog bred from two known parent breeds, knowing the coefficient of inbreeding of those two breeds and doing the maths to calculate the percentage for the mixed breed offspring when those breeds are crossed provides you with one way to express and view hybrid vigour for a dog or dog type.

You can then do the same for an alternative dog or dog type to compare them side by side in terms of which has the superior level of hybrid vigour.

The Kennel Club’s mate select tool allows you to determine the coefficient of inbreeding figures for every pedigree dog breed that they recognise, to enable you to do the maths.

Is it useful to know what degree of hybrid vigour a dog has?

Again, possibly. A high percentage figure for a dog’s coefficient of inbreeding (or a high figure relative to another dog you’re comparing them with) means a low, or lower, level of hybrid vigour.

The lower the level of hybrid vigour, the fewer of those superior evolutionary traits they will have, and so potentially, the more disadvantages/a higher propensity to hereditary health problems.

That said, even a really impressive degree of hybrid vigour (such as might be achieved in a dog that has multiple different breeds in their ancestry rather than just two – or a dog bred from a native British breed crossed with a dog from a breed only found abroad and so, that is hugely genetically distinct) is no guarantee of excellent lifelong health and a long lifespan, or other specific advantages!

However, with that caveat in mind, it is useful to know as you can then make an informed choice about a dog or have a fair prediction of what to expect on average based on the science being on your side or against you.