Rat Breeding Articles

Rat Breeding Part 2: Breeding for Exhibition

© Ann Storey MSc. FIBMS


Before you read this, you should first read Part 1.

There is an old saying about it being one thing to to get to the top and quite another thing to stay there. This applies to livestock breeding as much as anything else, especially with small livestock such as rats where the speed of their lives means that one month you can be at the top and the next have nothing to show and what's more, find your does are all too old to breed.

Starting Out

In my experience novice fanciers often do very well within eighteen months of starting to show providing they follow a few simple rules. These are:

  1. Foundation stock is good.
  2. They concentrate on one or two breeds only.
  3. They follow the rules of good animal husbandry.
  4. They pick one of the "right" varieties.
  5. They are keen and put a bit of work into it.

1. It is always important to get good foundation stock. First of all however you must choose the variety you wish to keep. Take time to choose a variety, visit shows and talk to the owners, is it really the one for you? Meanwhile, read and understand the standards. Handle as many rats as you can, whether they are good or bad, at shows and see why the winners won. Without handling an animal it is often impossible to see why a judge has gone for it. It is not unusual for a novice to win and not to have any idea why the judge picked it.

The two recommended methods are either to get all your rats from one breeder or get rats from several breeders and blend it. In each case these should come from established breeders of the variety you wish to keep. Rats in the NFRS are not expensive so therefore you should be able to afford the best; poorer quality rats, even if cheaper are a false economy. Do not go near the sales section at shows, the rats for sale here are often of inferior quality and novices are often tempted to buy them and use them. (The NFRS no longer has sales sections but some clubs still have them). Do not use rescues, although most people who carry out rescuing would not allow you to use them anyway.

Read Pro-Rat-a and see who wins regularly with your chosen variety, with luck you will have already spoken to them at a show anyway . Try to make sure that they have a record of winning over a period of at least one year. Once you have picked your breeder(s), try to visit their studs and get a good look at their rats so you can see how their animals develop at all ages. This is important, as seeing their rats at a show is only the tip of the iceberg. If they have no rats for sale at present be prepared to wait. Beware offers of rats from people who say their rats are "from the same strain" or "the same as" the breeder whose rats you have selected. It might well be, but in the meantime it may have been well mucked up! Never feel pressurised into buying rats you do not like the look of. This can be difficult, especially if the seller has bought the rats a long way to sell to you. When buying rats get a more experienced fancier to look them over for you if possible and be wary of pedigrees. There is no official pedigree or registration of stock system in the NFRS, although such schemes are in operation in some other countries. Most fanciers in the U.K do issue pedigrees, however obtaining a sheet of paper covered in the names of animals no one except the breeder has ever heard of is unlikely to be of much use to you. To be useful, a pedigree should contain a record of the colour and the breeding and show record of the ancestors should be available on request. Breeders should also tell you of any inherent problems in their rats, such as short tails, heath problems etc. It is important for you to understand however that there is no such thing as a perfect animal and that all strains carry some faults. Do not expect the breeder(s) to part with their best breeding and show animals. Breeding these animals is difficult for any fancier and they are unlikely to sell them to you! You are for them an unknown quantity, they do not know what you are going to do with the sweat of their labours so, while you should expect to get fit , sound breeding animals, close to the standard, with good temperament, you should not expect to get show winners. In fact some fanciers object to purchasers showing their rats and while you are perfectly within your rights to show it, you will be lucky to get any more animals off that person if you do.

There is some debate about the best age to buy breeding stock. If you want an animal primarily as a pet then it is better to obtain it at six weeks, but for breeding purposes I think that it is better to get them at around four months. This is because it is difficult to guarantee that a young kitten is going to turn out well and you may end up with an animal unsuitable for breeding at no fault of the breeder. Preferably get two does from the same breeder with the offer of a loan of a buck or return of the does for mating. Otherwise, buy the does already in kindle. This way you will have them mated (hopefully) to the most suitable buck in the breeder's stud. He is sure to be better for the purpose than any buck you are likely to buy. Don't worry if they are closely bred providing that the strain is a good and successful one. The drawback with this method is that you are effectively continuing the original strain and not founding your own.

Another way of starting out is to obtain stock from two or more different sources and blend them together. This is the best method for those with more experience but in my opinion can be rather too hard for the average novice.

2. It is also very important that you CONCENTRATE on one or at the most two varieties at once. If you are going to take on two varieties, try to pick two that can be bred together such as agouti and cinnamon, cinnamon pearl and pearl, Russian blue and Russian blue agouti.

3. The next important point is good husbandry. This is well covered in other articles. Suffice to say that more rats have been ruined by not being looked after properly than have been ruined by poor breeding. You should never get more animals than you can comfortably look after. Some points, such as condition and the thickness of the tail, are directly linked to the standard of care. Thin tails are not hereditary but caused by allowing does to rear too many kittens and by poor feeding in the first two months. Extra feeding after this time will not correct the fault completely.

4. Choice of variety. Apart from the new varieties, there are no "right" or "wrong" varieties for the novice. You should always go for the variety you like best. However you must be aware that some varieties have had very little work done on them and are not readily available. These varieties are unlikely to win. Also judges tend to be quite conservative and do not like putting up anything unusual. When you are looking for your variety, it is as well to talk to the breeders about judges' reactions. I am not saying that you should not breed them, just that you should be aware if you are going to have to educate judges as well! Of course, if you choose a very popular variety, it may be beyond you to beat the "big guns".

If you are a novice do not go for new varieties. These are a real specialist job and are liable to leave you disappointed and you are unlikely to do anything to further the breed. There are also many varieties that do not last well; these are siamese, himalayans, pearls, blacks, minks, chocolates, blues and lilacs. You will have to breed these regularly to have stock to show. Some varieties , such as the marked, produce very low numbers of showable rats and so you will have to breed proportionately more in order to breed a winner, although, once you breed one you can usually show it for a long time. Some varieties require more preparation than others, so there is no point in picking a light coloured rat if, like me, you dislike bathing rats! However, some varieties do much better in small studs than big ones; these include pearls and cinnamon pearls, pink eyed whites, champagnes, siamese and himalayans. This makes them very suitable for those who intend to keep a small number of rats in the house.

5. Keenness. It is very important to work at it. You can only expect to get out of things what you put in. Most regular winners have been working at it for several years to get where they are. Most of the time breeding results are not as good as you hoped and you certainly will not win all of the time, even if you think you have the best rat. While most of us have congratulated the winner through gritted teeth it is best if you can turn failure into a positive experience and resolve to try harder.

Breeding your first rats

When you have your foundation rats and they have settled in and are between four and five months old, you should breed them and not show them. As has already been said, some breeders do not like other people showing their rats but even if they do not mind it is a bad idea. This is because if they win you will keep on showing them and when you try to mate them they may be too old. I know many will not listen but I can assure you that I have done it myself and have seen it done many, many times. All does for breeding should be mated for the first time before seven months of age. Many can be shown successfully after breeding, in fact type and size are improved by a litter. First pregnancies in elderly does are more likely to end in complications leading to death of the doe or litter than at younger ages. It may cost you a big vet's bill! Trouble is it takes a will of iron to breed with a doe who you know could win the next show standing on her head. If you have a good one, and this goes for everyone, pick a specific show, such as the London or Bradford, after which you will retire her for breeding and stick to it! We have all chased that elusive last win but do not be tempted.

Planning your breeding - founding a strain

In order to get to and stay at the top, you will have to plan your breeding programme and unless you are going to be constantly buying new rats you will have to found a strain. It makes no odds whether you are principally a pet keeper or a fancier, if you are going to breed rats you should follow some sort of plan to enable you to breed good ones. It is possible to combine being a top fancier with being a pet keeper providing you pick a variety with a long show life and breed carefully. In fact some varieties, such as PEW, pearls and cinnamon pearls do better if kept in a small stud because they get more individual attention.

Founding a strain involves producing a home bred family of rats that all so closely resemble each other as to be distinctly of one ownership and it involves inbreeding your foundation rats. It is extremely difficult in my experience to found a good, healthy strain on one trio of animals. I've known a couple of cases of winning studs being founded on a trio of animals and bred on for years with very little outcrossing but in each case the original trio was composed of rats of excellent all round quality and a large dose of luck. Most winning studs are founded on a good original trio; have a few additional animals added in the first and second seasons and then an outcross every two to three years.

First litters

When your two foundation does litter, make sure that it is in separate cages. This is because it is necessary at this stage that you know what each doe produced. If you have decided to cull, remove all of the bucks if they are unmarked rats at four days old. If they are marked rats keep the best marked whether or not they are bucks or does, except that you must make sure that you keep some does. If you prefer you can put all the bucks under one doe and all the does under the other, providing you keep a record of who bred who. The reason for doing this is that the bucks are bigger than the does and by separating them you are giving the does more chance. You can only do this if the two does litter within a couple of days of each other. It is better not to leave a doe with more than eight babies. If she rears a big litter of 14 or more bucks and does, you run the risk of ending up with normal sized bucks and small does even if you feed well afterwards. Small does lack stamina and are of no use in the breeding pen. In my experience the size of the does is of more importance than the size of the bucks in maintaining size in a stud. It is not necessary to wean your kittens before five weeks, especially in the winter. After weaning, sex them and then run them on until you can see what you have got. When choosing what kittens to keep there is a small window of opportunity at about 6 to 8 weeks when the experienced breeder can pick out the good ones. After this time things get more difficult.When you are new to it however do not part with them too early or you may be getting rid of your best, unless they can go to a home where you can still use them. Try to get the original breeder to have a look at them, they should be able to guide you and help you to pick out the best ones. Slowly you should be able to see that two or three of them are superior to the others and if you are very lucky will have all the points necessary between them that you will eventually need to combine into one animal. The kittens should be at least as good on the whole as their parents. If they are not the mothers should be mated to an alternative buck and the first litter rehomed.

When selecting the kittens don't be tempted to go for the well balanced baby with the good colour/ marking,but average ears, eyes etc, although you can keep them for showing. These well balanced babies rarely make typy adults and type is very important when you are founding your strain. Once it is lost it is very difficult to get it back. It is easier to correct colour.

Showing and selection

With luck you should have some youngsters to show. Be careful. The ones that win are not always the best for breeding, so do not use success at shows as the only criteria for selecting breeding stock. Also if they lose first time out do not be disheartened. It will come in time. Talk to the judge but be careful with what is written in show reports and critiques and once again, do not use these as a way of selecting your breeding stock. All judges have their own interpretation of the standards and what one judge likes another one may not; altering your breeding according to the opinions of individual judges can have you running in circles. Some rats, especially bucks may take a very long time to develop their full potential. (I once read an article in Fur and Feather which said that all chinchilla rabbits should be put away for six months and not examined! The same could be said for rats!) Have a good look at the winners and see why they won. Showing at this stage however is an extra. What you should be concentrating on is selecting out two to four does for your next round of breeding. These does should then be sent back to the original fancier for mating. They should show you the buck they intend to use and explain why they are using him. It is far better for you however if they give you a choice of bucks and you make the final decision.

The brood doe

There is an old saying that I have heard regarding brood mares and bitches and that is that a good one has " the head of a princess and the rump of a washer woman". This is applicable to to rats as well. The heads on your does that you choose for breeding, should be long, clean in outline, broad as your thumb across the ears with big, well placed ears and bold eyes. There should be no trace of heavy jowls, short muzzles, narrow skulls, pointed (snipy) muzzles, rounded hamster shaped heads or the flat heads seen in Russian blues. A good head usually denotes good bone and rats chosen for breeding stock must have this. Does chosen should have a strong, well boned shoulder, back and rump combined with length and elegance. From the side the back should be smoothly arched over the loin when the animal is at rest and the rump should slope cleanly into the tail, not look as though the tail was stuck on as an afterthought. Too often good bone is taken as the same as large bone. In a doe this can lead to a coarse, masculine animal. The correct type is neither fine and narrow or coarse and heavy but must combine size and strength with grace and elegance, like a race horse, a ballet dancer or a Ferrari!

Remember that young rats often take time and you may have to run them on longer than you would like. Another important point is fat. Excess weight on a doe can be mistaken for large frame and give a superficial appearence of good type by smoothing out faults. However, she will still breed as a small framed rat with poor type if she breeds at all. Being very overweight is also harmful to her health.

The stud buck

If you have kept a buck from the first round of litters, you should be sure that he really is a good animal before you use him. This is of course true for any breeding programme whether you are a beginner or a greybeard! A good stud buck is not necessarily the same as a good show buck. Good stud bucks are usually ugly with no suggestion of femininity at all. Heads should be broad with bold eyes, a hump of muscle where the neck joins the skull, heavy well defined shoulders, no obvious waist, long and arched but not narrow over the loin and powerful in the hindquarters. Viewed from above he should resemble a housebrick tapered at both ends. When you pick him up the ribs should be well sprung to give a barrel shaped chest. The coat should be harsh but not long. Bucks take a long time to mature and can carry on growing into their second year. However, with time you will be able to select which of the young bucks are most likely to turn into a good buck. Providing your young buck has not got the same faults as his mother and the other rats including the babies, you can mate him to his mother and the other older doe. If he has got the same faults as his mother then you should not use him at all. If he produces good litters from the two older does he can be used on the younger does as well but not for their first litter. First they should be paired either with their father if they do not share his faults or, if they do, try a related buck that does not share these faults. The litters they produce should be carefully examined. If the youngsters are showing the faults of their sire (and grand sire) you know that you have used that buck enough in your stock. I have found that it is unecessary and unhelpful to line breed back to an individual further than grandchildren for reasons that I will explain later. If the offspring of one of the does is poor, i.e. not as good as her, then that litter should be rehomed. If all the offspring are poor then it is probably the fault of the buck. If the young buck produces good babies from his mother and the young does from their father then next time you can consider mating them together.

Take one step at a time and carefully assess each generation. This way you are more likely to pick up problems.

I always think that it is a good idea to use any prospective stud buck early. Try him at 4 months to a good producing doe. This way you will have a good idea of what type of rats he produces. If you do not use a buck until he is getting on you may well have missed out on a lot of good litters. Do not be afraid to replace a buck if you feel that a new one is producing better rats. Also remember that not all bucks are going to suit all does . This is another reason for keeping more than one stud buck. If you do only keep one then you are taking a huge risk because 1) he might be infertile, 2) he might die, 3) he might be carrying a major fault and 4) he might not suit all of your does.

Although most of us will carry on using old bucks until they die, you should be aware that most genetic diseases crop up in old males. This is because by the time a buck is over two, the sperm producing cells in his testis will have divided at least 1000 times and mutations will have crept in. While most of these will have no apparent effect, some will. These will not show up in the buck himself as they are in the reproductive cells only and will probably not show up in the buck's children, if, as usual, the gene is a recessive. However, they will show up in following generations. Many of these mutations may have tiny or inapparent effects but they can be acculmulative and lead to lack of stamina and fertility over the generations. Very occasionally a major genetic disease will occur (for instance 'fatty eye' in the BEWs we exported to Sweden). On the positive side the mutation could be a new colour.

Females are less likely than males to originate genetic problems, whatever their age at breeding. This is because the eggs are all formed while the doe herself was an embryo and the tissue which forms the eggs divides far less than the equivalent tissue in the buck, approximately 25 times.

Correcting faults

By now you will be on your third generation and should have some idea of the type of rats you are breeding, both its faults and its good points. If a fault is running through your stud, say, small ears, it will be necessary to correct it. The recommended way to do this is to obtain a rat with very good ears as a mate. This rat however is no good if it is not as good as your rats on other points or you will just add other faults. Preferably it should come from the same or a closely related strain. Mate this animal to yours and examine the offspring for any new faults and for the correction of the old one. The golden rules of stock breeding are:

  1. Never mate together two animals with the same fault.
  2. To fix a good point pair two animals with the same good point.
  3. Never breed with an unfit, sick or moulty animal. In rats this includes respiratory disease, skin problems, barbering, tumours and poor temperament.
  4. Do not average your mating, e.g. do not pair your worst buck to your best doe or your worst doe to your best buck. Always pair best to best and do not use the others.
  5. Be selective, it is a mistake to keep too many animals. Remember "God is not on the side of the big battalions, He is on the side of the best shots" Limit your stock to that which you can deal with easily, remembering that rats still need to be fed when you come in from work late and there is a foot of snow outside the rat shed door! Numbers vary but I would say that most varieties can be maintained using 4 -6 breeding does, 2-3 bucks and half a dozen rats "running on". Do not leave yourself just one buck. What are you going to do if he dies? I have known people lose strains because they did not keep enough animals and their key animal was infertile.
  6. To correct a fault, do not mate together two animals with the opposite fault but pair the faulty animal with an animal which excells on that point. E.g. if your rat has a short head, do NOT pair it with one with a long snipy head but to one with an excellent head. Other wise all you will probably do is introduce long, snipy heads into your strain.
  7. Traditionally, to maintain stamina, it has always been said that you can mate young animals together and old to young but never old to old. I would endorse this and add that while I do use does over 15 mths, you should only do so if the doe has littered successfully before and is in apparent excellent health.

Fixing your strain - Inbreeding

The task in hand now is the fixing and maintaining of your strain. Many people say that they have a strain when in fact they have no such thing. After three generations you have only the beginnings of one and it is still very much dependent on the parent strain. All strains are founded by inbreeding and all domestic animals have been inbred at some time in their development. It is the quickest method available to fix designated points. Inbreeding; the way animal breeders define it; is the mating together of relatives in order to fix these points. You can select for anything you want that the animal's genes are capable of providing. It is important to note that it does not create new genes but it can give the appearance of this by bringing latent tendencies to the surface. Critics of inbreeding often say that it causes small size, infertility and lack of stamina. Properly used, it doesn't. Inbreeding should be viewed as a tool. Its limits are set by the skill of the breeder and the gene pool of the stock. Problems with inbreeding mostly occur when the breeder has paid insufficient attention to a point, and, since the aim of breeders is getting winners (albeit healthy tame winners), fertility and stamina are often ignored. It is very important to breed with rats that are perfectly healthy and never suffered a set back or serious illness in their lives. The late Eric Smith; a founder member and life long mouse fancier, said that to me when I first started. I didn't believe him of course, any more than I believed that culling litters increased size, but I soon learned! Inbreeding should never be attempted using unsound stock. As regards litter size make sure that both bucks and does are fertile. To do this your virgin buck should always be put in with proven does and vice versa for your does. If no good size litters result, try them with other bucks/does. If it happens this time then they should not be used again. Litters should contain at least eight healthy full size babies. If she savages or does not care for them, repeat the mating. If she does it again, stop breeding with her, likewise if she appears to be a poor mother or has no milk. This is assuming of course that you have given her a cage by herself and plenty of nesting material.

Good inbreeding does not mean the haphazard crossing of relatives, even if they are show winners. Two relatives may be winners but a) they may not look alike or b) their faults and good points may not complement each other. Pairing should be along the lines I outlined earlier. Equally important to an animal's appearence is the points it is carrying. If a rat has had past litters you should be able to get an idea of these latent points both good and bad. If they have not bred then you must rely on pedigree. Most people's memories are not that good so this is where a good record system comes into its own. Don't fill this with flowery, subjective phrases of how good the rat is/was but be honest about it's faults. Never pair rats just because they are son/mother etc. Books often tell you about the comparative value of mating systems, e.g. father/daughter etc., while there is no hard and fast rule, here is my feeling on them.

Father - daughter: resulting offspring will contain 75% the genes of the father. Not just his visible points but also the invisible ones. Some of these will be faults! This mating to be performed when the sire is superior to the dam or has a point that you are trying to fix.

Mother - son: As above but the offspring will contain 75% the genes of the dam.

Grandparents - grandchildren: Only to be performed when the grandparents are really superior animals and have produced very well. Crossing back to a superior animal, whether sire or dam is known as line breeding. The idea is that breeding back to this animal will produce a strain of equally good animals. The problem with this is that the animal chosen as the foundation sire or dam is quite often not outstanding at all. It may be that the animal looks well enough, it may even be a supreme champion, but this does not mean that it hasn't got or isn't carrying a lot of faults. An example of this was the Champion silver grey buck "The mighty Thor", himself the son of champion "Flint", he was extensively used and bred back to and he sired a line of winners with good silvering but very poor heads. The influence of which can occasionally still be seen. It was evident early on that he was throwing poor heads, but as they won, breeders chose to ignore it, or maybe they did not notice it. This type of thing is mostly the fault of the judges. When you judge it is important to remember that those rats you put up are going to produce the next generation. If judges had not been so quick to put these horrible rats up then we would not have had so many problems sorting them out.

Brother - sister: These matings are the most controversial of all inbred matings. Most inbred laboratory strains are founded this way for ten to twenty generations. It is the fastest way to found a strain because no other mating throws up the good and bad points carried quicker. As with all inbreeding it is absolutely necessary to discard anything with a fault, poor stamina, health or temperament, because this mating, while it is the quickest way to fix good points is also the quickest way to to fix faults. Critics of this mating and I have to say there are many, say that it causes weaknesses and does not add anything. The first point; weaknesses, are only added if you breed with "weak" stock and are not careful to reject unhealthy or unsuitable animals. The conclusion that this mating does not add anything comes because it is said that you cannot breed offspring better than their parents. This is rubbish, remember that the offspring present the carried genes as well as the visible ones. Personally I would not use this mating on a long established strain as it is not necessary. Here most of the points that you want are already fixed and hopefully the major faults eliminated. I would, and do use it, in the early days of of a strain or among individuals of an outstanding litter. I would accept however that it is not for the inexperienced fancier.

Half brother to sister: where both rats share the same father or mother is often considered to be the most useful mating. It can either be a closely bred mating, if the other parent is also related or a less close mating if the other parents are totally unrelated. It is quite a good mating, especially when the shared parent is a good one.

In my opinion the appearence and pedigree of two animals is the thing that decides the suitability of the mating, not the animals' relationship to each other. I would not say that relationships can be ignored, just that it is not the be all and end all.

As I mentioned earlier, this is the animal breeder's definition of inbreeding. Geneticists define inbreeding as the mating together of animals with the same sets of genes, regardless of their relationship to each other.

If stock is carrying a lot of faults, such as usually happens with new varieties, then you do not want to inbreed but to follow a planned series of outcrosses alongside selection. Inbreeding should commence when the rats are basically healthy, tame and has among its members, most of the points you require in the strain.


Inbreeding, properly carried out, narrows the available gene pool down to those points we want (or think we do) because the others have been thrown out. After a few generations hard work you should arrive at a point where the points that the rats are showing are the points that the rats are carrying, i.e. the rat is homozygous for those points. This means that there is less likelihood of hidden faults appearing in the offspring and they will resemble their parents. When you get to this stage you can say that a strain has emerged. The problem with a narrowing gene pool, however means that a fault once bred in may be impossible to breed out. Also the rats may not adapt to change very well and the strain can also become "mediocre" or plain looking. Other problems that can occur are a drop in fertility and increased health problems. All of these problems tend to be insidious in nature and by the time you notice it could be too late. Whole varieties have become extinct in other species because of this . It is known as "Inbreeding Depression" and is partly caused by selection that has not been rigorous enough and conversely by throwing the baby out with the bath water and getting rid of some things you should have kept in! In very old strains genetic drift occurs, which means the acculmulation of mutations that have occurred during the life of the strain. Some of these may be good but most will not. All these problems can mean that an outcross is needed.

A "mediocre" strain is one of "well balanced" rats that do not excel in any area but have no major faults either. It comes from selecting medium quality rats for breeding. These are usually rats that the breeder has decided to let have a litter. If they have bred some good does, these have been shown until they are too old to breed and their less illustrious sisters have been used to carry on the family line. It is commonly believed that does can be of less quality than the bucks for breeding and this is the result. In order to avoid this it is a good idea to set a quality line each year. Look at all your rats of one variety, decide where they fail and agree to remedy this as your task for the year. Any rat which has no outstanding features or fails badly on the points you wish to correct should not be used. If you look at your rats and decide that the material to improve them does not exist in your stud then an outcross may be necessary. Outcrossing is a risky business and not to be undertaken on a whim. In my experience outcrossing is best employed to improve type, stamina and fertility, but colour and markings are best improved by selection within the strain. (This does not mean that outcrossing is the only way to improve the former points, frequently these can also be improved by internal selection). I think that outcrossing is best done using a doe although lots of other people recommend bucks. The reason for using does is because you are less likely to do a lot of damage with one doe as opposed to one buck. It is very tempting, if an outcross appears to work, to mate an outcross buck up to everything in sight. However, the problems with outcrossing in my experience is not in the first generation but in subsequent ones. The outcross doe chosen must be good all round but especially where your rats fail. She need not be a winner but must be a good breeding animal. The best outcross is a rat of the same variety from a related strain. If you can't find one in a related strain try one from an unrelated one or, failing that a related variety. Using a rat from a related strain increases the likelihood of the cross working or "nicking" (as fanciers sometimes say). In my experience outcrossing has two effects, either offspring appear much worse or much better than their parents. I've bred two show champions from outcrossing and sometimes the results are phenomenal. The problem is that the good "nicked" rat rarely breeds anything as good as itself.

Your outcross doe should be mated to your most suitable buck, then keep the best of the offspring, even if the outcross has not appeared to have worked. Mate a buck back to the mother and to one of his sisters. If the results are still poor, don't continue the project. If the results are good however and the original faults have been corrected, you can now carefully work in the outcross. She will bring in her share of faults and these must be selected against as they arise. You must also be careful to select against any rat with the original faults.

Line Breeding

Many people outcross too often and usually selection within the strain is better. A way round the need for outcrossing, especially in marked where outcrossing is extremely difficult, is the formation of separate lines within your stud. This means that you use each of your foundation does to found separate families or lines, using the buck as a common ancestor. Each family is maintained by line and inbreeding within the family. When an outcross is needed you can use one from the other line. Some mouse fanciers set up as many as four. However, I have not known one rat fancier who has successfully used this system because 1) unless you keep them separately or your records are very good they soon get mixed up. 2) If you have a good buck in one line it is tempting to use him on the other, 3) people often end up with a good first line and a poor second line. It can be a very good system providing you exercise self discipline and keep good records. If it can't work for you, forget it . You can have a top inbred strain without it. One way around this is the system Paul Threapleton and I had with cinnamon pearls and agoutis. Our rats had the same common ancestral stock and had annual swaps of stock after this. This worked extremely well and formed the foundation of many of the winning studs of these varieties today. I doubt whether either of the strains would have improved if we had not worked in this way. I firmly believe that it is important to pass stock out so that you can get your strain back if you need it and you also have ready made outcross material. This system is quite widely used among breeders today.

Lots of times outcrosses do not work. Most of you will have heard of hybrid vigour. This is meant to occur when two inbred lines are crossed and the resulting offspring are meant to be bigger fitter, leap high buildings in a single bound etc. Well sometimes this happens and sometimes it does not. It depends how well the genes "nick". Hybrids are not necessarily fitter/bigger or longer lived and sometimes the fault is not corrected. Earlier I mentioned the poor heads on silver grey rats. Improvement was attempted using rats with very good heads. However many times the heads were not corrected but went through the generations unchanged. This was probably because the genes that went to make up the shape of the head were somehow inherited together and passed on as a package. Sometimes this type of thing seems to have something to do with their environment but in this case it was unlikely as it happened in several studs. Where outcrosses do not work due to the reassortment of genes not being compatible the condition is known as "outbreeding depression". This is why it is so necessary to monitor all outcrosses so carefully.

It is important to remember that outcrossing is largely brushing the faults under the carpet and even when the fault appears cured in the first generation it is still carried by the ofspring. It is important that any reoccurrence is dealt with by not breeding with those animals.


There may be occasions where you do not wish to inbreed. This may occur because you are working on a new variety or your variety has a lot of faults, or you may simply not agree with it. However, people who do not like inbreeding and go for a deliberate policy of not mating close relatives tend to forget that they are just as likely to run into problems due to incompatible genes. Some books on livestock breeding give plans for random breeding systems but these are usually for the use of meat producers or for the breeding of laboratory or zoo animals. They are less good where selection to produce show animals is the aim, because random breeding is there to maintain the gene pool whereas any form of selection, by definition, narrows it. One plan which I have used which avoids inbreeding goes as follows:

  1. Obtain your foundation stock as usual and breed them.
  2. Keep the best two does from each litter, no bucks. Borrow two bucks from two other strains if possible.
  3. Mate one doe from each litter to each buck. Keep two from each, no bucks. If you started with two does you will have eight in the latest generation. By not keeping any bucks so far you will not be tempted to inbreed yet.
  4. Examine your rats. You can now attempt some like to like matings using borrowed bucks.
  5. At this point, you may keep a home bred buck and use him on the most distantly related does. However, do not use him more than once or twice.
  6. After this, you must decide how close a relationship you will accept in a mating. This is necessary as otherwise you may not be able to find suitable mates for your rats. Most people would not consider the mating of second or third cousins as being close. To avoid mistakes, good records are essential, do not use any doe more than once and any buck on more than one generation.
  7. During this time, do not lose sight of your breeding objectives, selection is still essential. Outbred strains will still carry health and fitness problems among others.

Like to like matings

This is a type of outbreeding where matings are carried out between unrelated animals that look alike. This is said to fix the good points in the same way as inbreeding but without the inherent risks. It can do this IF the reasons the rats look similar is due to them sharing genes. However, frequently the reasons why they look similar is not due to shared genes but chance and environment. Then the chances of the offspring looking similar are less than evens.


This is a condition where an animal consistently produces animals at least as good as and usually better than itself and all of one type. These animals are also known as homozygous dominants. If you breed one of these then you should make good use of it and line breed back to it as much as necessary. The animal can quite often produce good stock even when mated to quite poor rats. However, you must remember that the offspring will still be carrying all the other rat's faults! A properly used prepotent animal can found a dynasty, even if used in an outbreeding programme. A good example was the racehorse "Northern Dancer" who was the Sire and Grandsire of many Classic winners including Nijinsky, Green Dancer and Stormcat.


This section is last but it definitely is not least! There comes a time in every strain when it deteriorates past the point when one outcross is going to solve its problems. The reasons are usually due to neglect and may follow a time of personal problems, overwork, overstocking, too much winning or simply kennel blindness. The signs are; too many rats, cringing at the very thought of going in the shed, lots of weedy litters, insufficient cleaning, too many missed feeds, going to a show and coming back with a third out of two etc. If you cannot see your situation easing and you no longer have the time, money or interest to maintain your stud then you should dispose of it because it is not fair on the animals to keep them in bad conditions. If you do want to carry on this is what you do.

  1. Look at what you have. Get rid of all the weedy rats. Then spring clean the shed - this will make you feel better. Feed really well for one week.
  2. Now have another look. Hopefully you have still got a buck or two from before things went on the slide. Keep these along with the best four or five does. Get rid of every thing else. Pair these up.
  3. Do not exhibit or you will want give up.
  4. Cull the litters to four and when they are old enough have a good look at them. Do not breed again with the old does. I would get yourself a good outcross, either one or two bucks or two or three does. You will almost certainly need an outcross at this point as it is probable that a major degree of inbreeding depression will have set in.
  5. Look at the babies, keep the best ones. Either mate back to the outcross and/or to the original buck if he is good enough.
  6. Continue selection but do not show until you know you can give a good account of yourself.

If your problems are not due to neglect but simply due to a marked deterioration, possibly including severe faults such as maloccusion, then the same pattern of extreme outcrossing maybe necessary. In all cases severe selection is necessary in order to get improvement.