Breeding Tools

 

There are several “tools” that a breeder can use in a well structured breeding program. In order to breed Devons who are not just close to the standard but also healthy it’s quite important to have some basic genetics knowledge in order to make the choices that are more suitable to your own breeding program and to your goals.


These main tools are inbreeding, line-breeding, outcrossing and hybridization.

Let’s see each of them separately, but before doing so you need to know the meaning of a few terms. Just remember that you can check their meaning up here in case you forget!


Heterozygous - it means the cat has 2 different genes for a certain trait. In example a Short-hair cat can also be a carrier of the Longhair gene. This cat is called heterozygous for the Short-hair trait.


Homozygous - it means the cat has the same genes for a certain trait. In example a Longhair cat has two identical genes for the coat length. This cat is called Homozygous  for the Longhair trait.


Gene-pool - it is the complete set of unique alleles (genes) in a species or population. We can say that the gene-pool of the Devon Rex is given by the unique genes in all the Devon Rex cats existing right now.



Inbreeding


Inbreeding is the practice of breeding together cats who are closely related (parent to offspring, full siblings or half siblings) to each other. The purpose is to fix the wanted traits and to achieve type and consistency in the shortest time.


So, what does inbreeding do?

In technical words inbreeding reduces the heterozygous traits of the cat while increasing the number of homozygous ones.

In example, let’s say you breed together 2 full siblings with a short muzzle. This breeding will very probably lead to kittens with short muzzles, in which the “short muzzle trait” has now been fixed. Some of the kittens will become Homozygous for this trait. Some of them may show extreme short muzzles (shorter than the parents) because of this.

The purpose of inbreeding is to fix (make Homozygous) as many traits as possible in the shortest time. It’s possible to achieve great results in just one or two generations.


It’s important to understand that inbreeding does not do any magic!

You need good quality cats in the first place to make it worth. The reason is simple: in the same way inbreeding fixes a wanted trait (like a short muzzle) it can also fix an unwanted trait (like high placed ears).

So you can surely breed a pet quality female to her pet quality father in the hope of getting high quality kittens. But the result of such breeding will be kittens who have fixed traits, sure, but pet quality ones! No surprise then if you will find yourself with a bunch of pet kittens. As Roy Robinson says: inbreeding should be used when the selection has already happened and good type achieved, so that to fix the traits and get a more extreme look.


If inbreeding can lead to such great results and in such a short time-frame, why should we be so careful about if and when using it?

As it happens with most amazing things that do wonders, inbreeding has its own downside.


So, what happens when we do inbreeding?

Let’s say we want to breed together a brother and a sister. They both inherited the same “set” of MHC genes (the genes that contain the information to fight diseases) because they have the same parents (if you didn't read the article about immune system in cats it’s better you do before reading further).

When you breed them together you end up with kittens who have two sets of MHC genes, but one is the exact copy of the other. Instead of having a full set of diverse MHC genes, they will have 2 copies of the same one. With this single breeding we have just impoverished their immune system by half.

In the same way breeding together half brother and half sister (who share the MHC genes coming from on of the parents) we are weakening the immune system by 25%.


MHC1, MHC2, MHC3, MHC4==> they all contain information to fight specific diseases


This is what happens when you breed together unrelated cats:


Father (MHC1, MHC2)

- unrelated cats -==>Offspring (MHC1, MHC2, MHC3, MHC4)

Mother (MHC3, MHC4)


The offspring inherited 4 different sets of MHC genes and can therefore fight a large quantity of diseases.


But when you breed together full sibling:


Father (MHC1, MHC2)

- full siblings -==>Offspring (2xMHC1, 2xMHC2)

Mother (MHC1, MHC2)


The offspring doesn’t inherit 4 different sets of MHC genes, but 2 of the same kind.
Loss in diversity = 50%


While when you breed together half siblings:


Father (MHC1, MHC2)

- half siblings -==>Offspring (2xMHC1, MHC2, MHC3)

Mother (MHC1, MHC3)


Loss in diversity = 25%


Let’s now imagine the immune system of a cat who went through massive inbreeding for a few generations. The diversity will be heavily affected and the immune system heavily impaired.

It’s not something you will see right away. It’s not something you can test for.

It’s simply a matter of fact.


When you start to see the effects of an impaired immune system it means the damages have been catastrophic.

It won’t happen in just one breeding, but it will eventually happen if the inbreeding is carried on for generations without any outcrossing or hybridization in-between. It’s called inbreeding depression and it refers to the impaired ability of very inbred cats to fight many diseases, sometimes becoming weak to specific ones.


You can recognize inbreeding depression in cats with one or more of the following problems:

- reduced number of kittens per litter

- fertility issues

- reduced weight of the kittens at birth

- increased kittens mortality

- susceptibility of a cat or a group of cats to a specific disease


The first points are quite straightforward, while the last one is a very interesting effect that happens in group of cats who have been part of the same breeding program. In a few generations the group ends up with a weaker immune system, being resistant to the same diseases and very susceptible to the very same one/s. As a result the cattery has endemic diseases that is unable to get rid of, because the cats immune systems are unable to fight the infection and even the proper treatment may have little effect. It can happen with a virus like Herpesvirus, or with other diseases that usually affect a moderate percentage of the population, but at some point start to affect and kill a much higher number of cats in specific groups of cats.


Based on all this, is inbreeding safe?

Inbreeding is an amazing breeding tool and can be used in a breeding program. But it’s not for everybody. It should be used only by expert breeders and taking into account some important factors.

You first have to find out how much inbreeding has been done on that beautiful cat you just bought before considering it. Based on that you can have a pretty good idea of how strong or weak the immune system is and what breeding tool would be best used to get both type and a better health.


Never forget that the inbreeding percentage of a cat is just a number. What is really important is to check how much inbreeding has been done and for how many generations. In such a research it would be better not to stop at the first 5 generations but to dig deeper.

A cat with a 4% inbreeding in the first 4 generations can end up with either a 12% or a 30% total inbreeding (total inbreding is the inbreeding percentage you can calculate on the more possible generations available, usually using a pedigrees tool or pawpeds.com) making things quite different.


Inbreeding is a very powerful tool and can lead to beautiful cats. It’s our responsibility as breeders to make sure it doesn’t lead to immune system impaired cats as well and it doesn’t lead to genetically impoverished cats.


Linebreeding


Line-breeding is a term used by breeders and it's used to identify a moderate inbreeding. It refers to breeding related cats together, but not as closely related as in inbreeding. An example of line-breeding is the mating between cousins.


Geneticists do not use this term and they refer to any breeding between relatives as inbreeding. This term has been introduced by breeders to distinguish between more or less aggressive forms of inbreeding.

I think it’s a legitimate distinction as even if both breeding practices involve breeding together related cats there are some differences between them.


So, what does line-breeding do?

It does the same as inbreeding does! It reduces the heterozygous traits of the cat while increasing the number of homozygous ones.

It leads to uniform and homogeneous litters and fixes the wanted traits in the offspring.

The main difference from inbreeding is that this process takeslonger to achieve the same results.


So why, if it takes longer, we should use it instead of inbreeding?

Line-breeding leads to a less dramatic decrease in the diversity of the cat immune system. It still happens, as you are breeding together cats who are somewhat related but, depending on the type of breeding, you will be reducing the diversity of a much less significant portion than with inbreeding.

In example breeding together 2 cousins will sure mean a little diversity will be lost, but it will not be as significant as the 50% loss we have by breeding together full siblings.


Line-breeding can lead as well to inbreeding depression, there is no way out of this. It may take longer but it will eventually happen if it’s not used with moderation.


Like with inbreeding it’s very important to know the history of our cats. Check how much inbreeding or line-breeding has been done in the past and only based on that you will have the necessary information to decide if line-breeding is the right tool for your breeding program.


Outcrossing


Outcrossing is the practice of introducing unrelated genetic material in a breeding line by breeding together cats of the same breed but with different lines.


The whole idea of outcrossing is to increase the diversity of our cats by breeding them to a different line. As you can imagine there is no complete outcross possible in the Devon Rex because all cats go back to Kirlee!


Still, it’s considered outcross any mating between two cats who don’t share a cat in the first 5 generations. Outcross can be used both as a breeding method in itself, or as an efficient way to restore health in an inbred cat or line.


The main goal of this breeding practice is to increase genetic diversity. It’s also a good way to restore vigor, fertility or health in a breeding line.


If you have been working with highly inbred cats you will immediately notice some differences in the offspring coming from a well done outcross. The kittens will be bigger in size, will less easily get sick or be easier to treat in case of infection. If your cattery is affected by susceptibility to a specific disease a single outcross may drastically improve the situation.


So, proven that oucrossing improves the diversity of our cats, how does it affect their type?

It depends on many factors that should be taken into account.

When using outcrossing as a breeding method there are basically two ways of taking the best out of it.

The first one is to only breed cats of good type together, while the second one is to breed together cats who are complementary in type (that means to breed a girl with very short muzzle but high placed ears to a boy with a little longer muzzle but very low placed ears).

The first method will more easily produce quality kittens, while the second one is a little more like gambling.


Now, the outcome is usually a surprise as you never know how those two different lines will interact with each other and there’s no way to predict the kittens type. Only experience will help with that.

What usually happens is that the litter will have one or two very nice kittens (sometimes with good type, sometimes with amazing type) while the rest of the litter is poor quality. This is no surprise. The homogeneity of a litter is closely related to the genetic diversity. When most of the traits are fixed with inbreeding it’s normal to have homogeneous litters. At the same way it’s normal to have a bigger diversity in a litter coming from an outcross.


Hybridisation


Hybridisation is the practice of breeding two cats from different breeds together to widen the gene-pool and achieve hybrid-vigor.


We said above that outcrossing will increase the diversity of our cats, while hybridization will widen the gene-pool.


But what’s the difference?

The gene-pool is the complete set of unique alleles (genes) in a species or population. We can say that the gene-pool of the Devon Rex is given by the unique genes in all the Devon Rex cats existing right now.

Outcrossing will redistribute the already existing genes.

Hybridisation adds new genes coming from a different breed and therefore widen the Devon Rex gene-pool. The implications are many: as we said before the Devon Rex was selected with inbreeding and therefore lost diversity in its very start, a diversity that cannot be restored in any other way but hybridization. This breeding practice introduces new genes, new MHC genes and new information coming from breeds that went thought a total different path and therefore may have a quite different gene-pool.


Hybridisation should not be done lightly. Also in this case there are several things to keep into account before using this breeding tool.

Health and type are the main ones.


It’s important to use cats from breeders we trust and we know coming from healthy lines to avoid the introduction of diseases not present in the Devon Rex breed.

Hybridisation is an important tool to bring vigor into the breed, and even if this is its main goal we cannot forget what makes the Devon Rex such a unique breed: look and temperament.


Using another breed will mean to a step back in the selection of the Devon Rex type.

Still, we can “contain” this by selecting an appropriate match.

It’s very important to find a breed that is close enough to the Devon Rex type so that tje selection will not be out of reach.

In the past Sphynx and Siamese have been used for hybridization. As you can imagine the results have not been amazing. The loss in type was too huge and it also brought along nakedness issues. Using a breed that is too distant in type will make it barely impossible to have the Devon Rex type back if not with a very hard and long work.


The best choices are those breeds with a morphology similar to the Devon Rex but with faults that bring them closer to our standard.

A good example is an American or British Shorthair with big ears. Such a subject is considered a pet for the ASH or BSH breed, but would be perfect as a match with a Devon Rex cat. The muzzle type is already quite close to the Devon one (and it happens to even bring improvements in type) and using a subject with big ears will make our life easier in the selection of the next generations.

The same applies to the Devon Rex with which the mating will be done. It’s important to chose a cat that is quite close to the standard to have better chances of a nice offspring. The traits that are most important are the ears, that must be large and placed very low to compensate the small and high ears of the other cat and the overall look that must be as devonish as possible.

The choice of the right subjects is vital to the good results of this practice, in both type and health.

As inbreeding, also hybridization is a tool that should be used by more experienced breeders who have a clear idea of how to select for the Devon Rex traits.


You can find below a table with a recap of the pros and cons of all breeding practices that may be easier to read.