Saturday, 22 October 2011

What is Line Breeding?

To answer this question in one word, it is inbreeding. However the word inbreeding has unpleasant connotations, particularly to the layman, so line breeding is a phrase used by breeders who practice this. Basically any cat that is mated to a relative is being line bred. A lot of people – especially novice breeders– shy away from this idea. This may be because, in human terms, any mating between close family members is frowned upon and indeed seems slightly horrific. Some of this distaste may rub off onto our views about cat breeding. However it can be a useful tool when used intelligently. Moreover, cats have no such compunction and mums are happy to mate with sons, grandfathers with granddaughters and so on. Obviously what cats are happy to do and what is in the breed’s interest does not always coincide. In the following article I will use the term “inbreeding” rather than line breeding as I feel it is more honest.  I'm not into inbreeding my cats in a big way myself and use frequent outcrosses, but sometimes having a really good ancestor on both sides of the pedigree can produce wonderful kittens, so long as health is always top of the list of priorities.
Quink as a 'teenager'
Let us look at Quink's pedigree as an example.  His pedigree name is Quil Gyldenloeve.  Because he has a very short pedigree he is on the 'reference register' for GCCF.  You only have to go back three generations to find a 'novice' - ie a cat from the forest (Champion Putte), of unknown ancestry.
So we don't know if Putte is inbred or not.  We can but hope!  The rest of the pedigree looks as though there are no other cats appearing more than once - so he seems to have no inbreeding at all.  However if you go back... and back... and back to the ends of all the lines in his pedigree, you can see that a few cats do appear more than once after all.   It's very slight though.  

So what happens if you avoid inbreeding?

Well, for a start, in the world of Norwegian Forest Cats it is very difficult to avoid some measure of inbreeding as some cats (particularly well-used stud cats) appear in pedigrees time and time again, albeit possibly so far back in the pedigree that the breeder may not realise without special research. This is in spite of NFCs having one of the widest gene pools of all breeds. In my opinion, some of the early breeders of Forest Cats in Norway did repeated matings of very closely related cats, to an extreme extent, and that is not something I would like to see happen again. A certain amount of diluted inbreeding is seen in many breeds and so long as the common ancestor(s) do not have health or temperament problems then it is harmless. However if one tries to have little or no inbreeding in a pedigree then what happens is that the results of a mating are very unpredictable. That is why there are huge variations within the NFCs in this country and indeed worldwide. There are also enormous variations within individual litters. Experienced breeders are often pleased when they have some sort of uniformity within a litter and within litters of repeat matings. Sometimes they are fooled when the kittens are all one colour and pattern however! Otherwise breeding NFCs amounts to little more than a lottery. I have seen (both in my own cattery and in others) cases of large parents producing small offspring; small parents producing good-sized offspring; two cats with dipped profiles producing kittens with straight profiles; and vice versa, and so on. It always amazes me how variable NFCs are, after I bred Abyssinians for some years with very predictable and consistent results. The latter is probably due to a much smaller gene pool in the breed as a whole – something that has its advantages and disadvantages.

Vieuxtemps Indigo

We once had an 'oops' mating that resulted in father-daughter progeny!  This was when Magnus had been neutered but was still fertile.  He was mistakenly allowed to reach his daughter and, sod's law, they mated.  The result was two lovely and very similar blue tabby kittens, Indigo and Indiana.  

Champion Magnus More og Romsdal, father of Indigo

A father-daughter mating certainly wasn't what I had had in mind, but the kittens were robust and beautiful so no harm was done on that occasion.  

What happens if you avoid inbreeding to a large extent, is inconsistency and unpredictable type. Resulting litters are likely to be healthy and large but may have hidden recessive defects.

We are fortunate to have a large gene-pool for the NFC breed, worldwide and also within the UK. This means that we have a wide choice from which to pick and choose the best of the cats available to breed on from. Of course this doesn’t always happen as some breeders use cats for breeding merely for reasons of convenience or sentimentality. However we are in a better position than many breeds when it comes to diversity of breeding stock. So should we make a point of capitalising on this fact and doing as many outcrosses as possible in our breeding? To answer this question we need to know the answer to another:

What happens if you do practice inbreeding (and probably call it line breeding)? 
There are some good things to be said for inbreeding. The obvious one is that litters become more consistent. If a cat is “doubled up” in a pedigree then that cat’s characteristics will have a doubly strong influence. When a cat is considered a particularly brilliant example of a breed then sometimes it appears in a cat’s pedigree many times. I counted the repetition of one such “super cat” in a UK pedigree and it appeared 13 times in just a few generations! Before you drawback in horror let me also say that the cat whose pedigree I mention is actually a reasonable size (as far as I can tell from looking as I haven’t handled him), healthy and very successful for a number of years both on the show-bench and as a stud. Hence in this instance the inbreeding cannot really be faulted even if most of us would avoid such extreme practice.

Another benefit of inbreeding is that, if there is a recessive genetic fault in a cat, then it will very likely be revealed in the inbred offspring. I remarked above that a cat who is doubled up in a pedigree will have double influence on the genes (depending on how far back the doubling up occurs, of course). Let us take as an example the father-daughter mating I had many years ago, by mistake. The father had no known genetic defects and was a healthy, good-looking cat. However he may have had a recessive fault. If that had been the case then that fault would only “show up” if his mate carried the same fault. With unrelated mates this would be unlikely. Some genetic defects can be secretly carried for generations just because the cat with the recessive (hidden) defect has never been mated with a cat also carrying the same recessive defect. If you have a doubt whether or not a cat is carrying a recessive defect then you can check it out by repeating the suspected carrier in a pedigree. If no kittens in the resulting litter have that defect it is very likely that the suspected cat is free from the defect.  That is fortunately what happened with my “oops” mating mentioned above.

So, with inbreeding, the faults but also the good points are doubled up in the progeny. Hence if a cat with a very strong chin, for instance, is repeated within a pedigree twice or more times, then that strong chin is more and more likely to appear in the kittens. Something happens that we call “fixing” a characteristic; and if intelligent line-breeding has taken place over a number of generations with the breeding stock carefully selected from each generation, then the “look” of that line is firmly entrenched and is likely to be passed on even to the offspring of an outcross mating.

This Vieuxtemps  litter brother and sister, from completely
unrelated parents, are inconsistent in type
To sum up, the benefits of inbreeding are discovery and hence elimination of any hidden genetic defects, together with a consistent and distinctive “look”.
 If inbreeding has been carried out then it is wise to use outcrosses frequently also. An outcross is a mate with very few or no shared ancestors. Repeated inbreeding can cause “inbreeding depression” meaning not that the cats go moping around miserably, but that individual kittens and also numbers in litters decrease in size. If you mate two very closely related parents, even if those parents are huge cats, offspring are likely to be smaller.  Conversely, an outcross can immediately restore the size of the individual and the size of the litter (assuming that the individuals concerned are large and fertile of course). This phenomenon is known as “hybrid vigour”.

If you look at the pedigrees of famous and successful breeders here and abroad (for example, the Pan’s cats of Norway and Jette Madsen’s world-winning Felis Jubatus lines from Denmark) you will see that they have carried out inbreeding but also included plenty of healthy outcrosses. If a cat has been extensively used and repeated in pedigrees – Pan’s Polaris is perhaps the most famous example – then it is fairly certain that that cat has no genetic health problems if these have not shown up in multiple progeny.

My previous stud cat, Dansbjergs Pelle Halelos as a youngster.Pelle had been purposely line bred to 'fix' some excellent characteristics
and as a result his litters were very predictable and beautiful.
Vieuxtemps Vantage Vroom, Pelle's son, was from a complete outcross mating yet looks very like his father due to Pelle's specially bred 'fixed' look.Vroom has done very well on the showbench.
So what should breeders do? My own experience of this is that I have done both inbreeding and complete outcrosses. With the inbreeding I have immediately seen a particular “look” which more or less replicates the look of the cat that was repeated in the pedigree. Naturally I have used cats that I really like as “repeats” so the resulting look is therefore one that pleases me. When I imported my stud Pelle (above, now retired) I chose him because he comes from completely different lines from my existing cats. It was time for a thorough outcross. However he came from a breeder who has, over many years, performed careful and intelligent inbreeding so that her cats have a distinct “look” incorporating the features she considers important in the Norwegian Forest Cat. This has been done so effectively that I find that kittens from that stud, resulting from unrelated females of mine and other people’s, tend to carry on his distinctive and predictable “look”. This is because the stud has fixed characteristics due to the way his pedigree was planned. Of course, his bad as well as his good points are likely to be fixed – fortunately he appears to have no genetic defects. I feel my own way forward would be to continue to combine inbreeding with outcrosses in an attempt to maintain the “look” whilst at the same time achieving hybrid vigour. Of course breeding high quality cats is easier said than done, which is all part of the fun.  I am writing this article to clarify what the good and bad sides of inbreeding are, and to dispel the myth that all inbreeding is a bad thing. It can be a good thing too – in moderation.

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