This article is based on my personal experience as a pet owner and running a small private rattery since 2002. It also takes into account the personal experience of other private breeders. It is not a guide to commercial breeding, which has its own challenges and experiences.
Breeding any animal is not something to be taken lightly. You will be responsible for bringing living beings into the world and their fates and the quality of their lives will be up to you. I am not going to impose my own ethics on you, but you will have to form your own and be willing to stand by your decisions and defend them.
Before you jump right in and breed, I recommend you read the following articles (in addition to mine of course) that will help you understand what you are getting into:
"The Responsible Breeder"
The Responsible Breeder Code of Ethics
Breeding: Can YOU live with it?
Should I Breed My Rats?
Misconceptions vs. Reality
First, let me dispel some reasons people have for breeding that just aren't true. Here is reality for you:
There are no health benefits to rats that are bred. A female that has a litter is not less likely to develop cancer. She is, however, more likely to develop a serious infection, come down with a case of myco from the stress of motherhood, and on average has a shorter life expectancy than rats that are not bred. Pregnancy and giving birth carry added risks of complications, which can even be fatal. (Tumors are caused by a rat's hormonal changes in old age. The most effective preventative is spaying when young.)
Rats can live a happy and "natural" life without breeding. I've even heard people with cats and dogs say they won't neuter their animals because it's not "natural," because they think an animal needs to experience parenthood for a full life. This isn't true. Yes, in the wild, almost all rats that hit sexual maturity do reproduce. However, in the wild, rats do not live past a year old. In the wild, rats die giving birth just like they can in captivity. In the wild, rats are exposed to extreme temperatures, diseases, and predators too. Our purpose as owners is not providing domesticated animals a "natural" lifestyle, it is providing them a happy and healthy one.
Small-scale breeding is not profitable. To make money breeding, you're talking about running a business, maintaining facilities, and breeding large numbers for instututions and/or stores. To the private breeder, producing one to four litters a year and placing in private homes, you will not make money. You will spend it. Breeding means extra cages and more food and supplies. It increases the stress on your animals, and higher numbers mean a higher risk for disease and more medicine to treat it. It can have other costs as well including website hosting, travel, registration, etc. The pups you sell will not compensate for their cost.
(Not that breeding isn't worth the cost in its intrinsic value, but you have to be willing to make some monetary sacrifices along the way.)
Your Purpose & Goals
You need to have a reason to breed. Ask yourself seriously: Why? Some common answers are to have more rats of a certain color, because you love rats, to make some extra money, or for the experience. These reasons are vague and the first two just have no good backing since there are so many rats that need homes. If you want to make money, you will likely need to be a supplier to a pet store or institutions or sell rats as feeders. If you want "the experience," then realize that you might not be able to find homes for the offspring and there are costs and risks involved.
To narrow things down, people breed for three main goals. Resale/money (usually feeder or lab animals), pets, or show/breeding.
Now time to be specific. Decide on some specific goals. These depend on your purpose. If you are breeding for pets, you need to consider the factors that make good pets, especially good health, temperament, and the colors and types that people are attracted to. If you want to breed show animals, you need to consider all these things, but also more detailed goals including the hue of color, the shape of the body and head, and the quality of the markings and fur. (Take your rats to some shows to get pointers on good type and color.) If you breed rats as reptile food or for resale, your goals will have more to do with size and survival rate (breeding rats that have large litters and few still births).
Don't be vague about your goals. Instead of saying good health and temperament, specifically plan out that, for example, you want your rats to be resistant to myco by never breeding sneezy rats, megacolon-free by discontinuing lines where MC occurs, and state exactly what kind of temperament you feel is "good," whether they are sedate and calm or more playful animals you are looking for. Also, decide what your priorities are. If a rat is sneezy, but has good personality and good markings, will you breed him? What about a healthy rat that is a little nippy?
Make sure to never lose sight of your goals. Every generation should improve on the one before it.
Even if you don't want to breed often and aren't into technical science stuff, you will need to know at least a little about inheritance to produce litters that are the colors and types that you and/or your adopters are attracted to. Remember that color, markings, and type are what adopters see first and can be as important to some as health and temperament.
Without going into genetics, you'll need to have at least a basic understanding of a couple of things. Many of the attractive traits are not ones that simply pass on to offspring unless both parents have or carry the trait. (In genetics terms, they are called recessive traits.) That means if you breed a blue rat to a siamese, you will not get blue siamese; in fact, unless the siamese had a blue parent or the blue had a siamese parent, you will get neither. Black is the color of rats from such breedings or agouti from agouti-based colors. Although not true everywhere, it is sometimes harder to find homes for black rats because they remind people of plague rats, and agoutis look like their wild ancestors. A blue bred to a blue, however, will give you all blue babies. A siamese x siamese will result in all siamese. Other traits that behave like this are hooded markings, dumbo ears, hairlessness, albino, beige, champagne, chocolate, and mink.
SOME traits are passed on to offspring as long as one parent has the trait. (These are called dominant traits.) These include agouti, black, and rex fur. Sometimes it is a little more complicated. Two rex parents may produce some rex, some normal furred, and some double rex, but a double rex bred to a normal furred rat will give you all rex babies. Manx and many white markings are complicated and work differently than other traits. These are varieties that should be bred only by people with genetics knowledge.
One of the most important inheritance issue you will need to consider is the inheritance of disorders and deformations. One infamous inherited (and always lethal) disease is megacolon, in which the muscles in the sphincter, colon, and/or cecum are paralyzed and cause rats to look bloated and deformed and die before they are eight weeks old. Though it hasn't been pinpointed as to what specific genes or combination of genes cause MC, it has been linked to lines with heavy white spotting, blazes, and/or odd-eyes, but it has been known to occur in lines that have none of these. If MC shows up in a litter, you should seriously consider discontinuing the line. Other problems that can be associated with specific varieties spinal problems in Manx rats and inabilities of hairless rats to produce enough milk for a litter. Also, deformations may show up in your line (especially a heavily inbred line) such as extra toes, short or kinked tails, or even missing eyes. Such deformed animals should not be bred (nor should their relatives in most cases).
Remember that a pedigree is an extremely useful tool for determining inheritance. If possible, try to get your rats from a breeder who can supply one.
For genetics information, see this page.
The Importance of Pedigrees
Beware breeders that don't keep good records. It isn't that they don't care about their animals or aren't breeding responsibly or taking care of them, but not keeping records defeats the goals of breeding--to improve rats as a whole, to develop healthier and friendlier lines. How can a breeding program go anywhere without a "map?" When a breeder doesn't keep good records, that tells me that they are not working on a line, but are simply bringing more rats into the world. They might be great rats, healthy and well-socialized, but the breeder lacks direction.
A pedigree is not a status symbol. It doesn't mean that certain rats are "better" than others. It is a guide, a tool for keeping track of a line and seeing how it has and will develop. A pedigee's most obvious value is one of predicting and planning genetic outcomes. By looking at pedigrees, a breeder can tell what genes his or her rats do carry or could carry. This allows them to find compatible couples and plan lines, not just the next litter, but generations down the line. The heredity predictions go beyond just planning pretty colors. A breeder can look at prefixes, find breeders of ancestors, and keep track of any news about those breeders lines. Do they live long? Have there been aggression problems? What about hereditary disorders? A pedigree allows a breeder to check up on things and know their lines thouroughly--not just colors but the overall rats.
Finally there are more subtle aspects of the pedigree. A pedigree shows how many generations of rats were bred by people who cared enough to keep track of their family. A pedigree shows that two rats were put together deliberately for the purpose of breeding a good litter. "Feeder breeders" and "wholesalers" usually do not have records of parents, because they simply keep males and females all together and let them breed freely, so they don't know who dad is; half the time, they don't even know who mom is. A pedigree will tell you that these animals had NAMES and purpose. They were loved pets. It also can show you how much inbreeding there is in a line and how closely related all your rats are, and that can affect health tremendously.
So, are pedigreed rats "better" pets than non-pedigreed ones? No. But if you are breeding, a pedigree IS important. The longer the pedigree, the more useful a tool it is. Keep track of your rats' families, and get your rats from breeders who keep good records.
How bad is inbreeding? Well, it is about as bad as it is good. People are often squeamish about it due to our own social norms, but no such norms exist for rats, so we need to approach this from a scientific veiwpoint. Inbreeding is a powerful tool which may become a dangerous one. It strengthens traits present in a line and reveals genes that are carried--both good and bad. This is how new colors come to be discovered, but also how new deformations and disorders occur.
Random mutations occur in genes very infrequently. Whether good or bad, these genes may stay hidden and vanish from existence as long as the animals in question never reproduce with another animal carrying it. For example, a rat might carry a gene that would produce babies with no eyes. This bizarre gene probably doesn't show up all over the place, but it will likely be carried (not shown) by the offspring of that rat. If one of these offspring are bred back to that original carrier or to another one of the offspring, you may have a litter that contains one or two eyeless rats... Of course, this may happen with "good" traits, too. Most new colors/types either appear or are developed through carefully planned inbreedings (usually in combination with breeding to healthy lines of unrelated rats). In general, inbreeding should be practiced sparingly and with caution, only in combination with outcrossing in order to keep a strong and diverse gene pool.
This is one of the most frequently asked breeding questions. What is the "safe" breeding age? There aren't any exact numbers, though lots of people like to give them for simplicity sake. The truth is, a rat can feasible reproduce any time after it becomes sexually mature and can continue until it dies (or until its health diminishes with age), but both ages can vary from rat to rat. Of course, if you want to consider health, stress, and complications, it becomes a little more complicated and often debated.
For your male, his growth and stress aren't too much of a concern. Breeding isn't very stressful for him unless the female beats him up. Males usually become mature 6-8 weeks old. It is a wise idea to not breed any male until he is at least six to twelve months old. By that time, health concerns and aggressive behavior will be apparent (this is especially important if you don't have a pedigree and/or knowledge of the male's parents). Males can be bred throughout their lives as long as they are healthy. It is more important to make sure your male is healthy and has no inherited or contagious diseases he can pass to the female and offspring. If you are breeding rats for long lifespans and health, consider waiting even longer to breed males, even 18 months to two years.
Female breeding age is a bigger concern. They are sexually mature at the around the same age as males. It is best to wait for her to be done with most of her growth, so she won't have a strain of resources, trying to grow and to carry/nurse a litter as well. This age is around four months old. After this age, the younger the rat is, the "safer" it is to breed her. There is a claim that females' hips fuse if that don't have a litter before they are eight months old. It can't be said for certain if this is a fact or not, but it is true that the risk of complications and lack of maternal interest increases with age. As a general rule, females should be at least 5 or 6 months old and not older than a year when bred for the first time. After a female weans her litter, it is best to give her a month or two before breeding her again. Some females go through menopause at 18 months old, but others may be able to breed their entire lives. Regardless, it is best to stop breeding her at this age, because complications,and small, sickly litters are a risk in older rats.
Here is a quick overview/comparison of female rat development:
Females go into heat every five days for 12 to 24 hours. You can tell she is in heat because she'll be more hyper than usual, and may freeze and quiver when touched. Some rats don't do this or don't have such obvious signs. One method of breeding is to put the female and male together for this period. If your female doesn't do anything obvious to indicate she's in heat, try putting them together every day until she lets the male mate with her. An alternate breeding method is to put the male with the female(s) in another cage for a week or two. It is best to introduce them on neutral ground, such as an extra cage or aquarium. Never put two males in a cage with a female or females, because they may fight (and you won't know who the father(s) of the litter is). It is possible and not too uncommon for litters to have more than one father if the female breeds with more than one rat during her heat cycle. (Of course, each baby rat will have ONE father.)
How do you know your rat is pregnant? Well, there are signs, but unfortunately none of them happen to all rats for all pregnancies. Most rats will show at least one or two signs, though. (In rare cases, you'll have a rat that seems to just be perfectly the same as always until suddenly you have a litter on your hands!) Just to note, gestation for a rat is typically 22 days (20-24 days is an average range). Here are some signs that you may observe:
The most important thing to keep in mind when your rat is pregnant or giving birth is to let mother nature do its job. Sometimes a pregnancy might last several days onger than you expected, or your rat might go into labor and then stop for a long time. A little dischange is not a cause for alarm, neither is it when your rat seems uncomfortable. Don't pester the mother to be. She is perfectly capable of delivering her own babies and caring for them. In the vast majority of cases, the best thing for you to do is be an observer and leave her alone. Even if the mom is apparently ignoring babies or separating a few of them, it is usually normal. If anything concerns you, before you disturb the mother/babies, talk to a breeder with experience (not a ver unless they have bred rats--most breeders are more knowledgable than vets on this subject).
Roughly 22 or 23 days after she was bred, your female will have her litter. You may or may not see it. If the male is still with the female at this time, remove him immediately. Though rats generally are wonderful fathers, females go into heat immediately after giving birth, and being pregnant while nursing can be a real strain. The first signs of birth will be a little blood on the bedding and/or birdlike chirping. Rat litters can range from one to over twenty, but most litters contain six to twelve pups. (The smallest I have had personally was two, and the largest was 16.) Rats are born hairless, blind, and deaf. If you look closely, you can see their little whiskers, fingers, toes, etc. They rely on their mom completely for warmth and food.
New moms can vary. Some may ignore their offspring for a half hour or so, until their instincts get a chance to kick in. It is important that you give her a chance and keep the room temperature warm until she figures out what to do with the babies. If after an hour, you can't see white (milk) in all the babies' bellies, you should start looking for a foster mom or be ready for hand rearing them (discussed later). Newborns can be handled if the mom lets you. Don't be surprised or angry if the mom bites you. Some rats are very protective of their babies. Most rats will let you touch or hold their little ones or even let you baby-sit while they take a short break from motherhood for ten or twenty minutes, and won't kill or reject babies you've touched (as is the common misconception). Of course, there are "bad" moms in the rat world, so you may want to be cautious by rubbing your hands in the nesting material before you touch the pups.
A lot of bad things can happen with a litter, regardless of how well you plan and care for them. Especially in larger litters, you may have stillborns (babies born dead) or pups that die shortly after birth. This is not your fault or the mothers' fault; these babies just didn't have what it took to survive. Moms may set the babies that are going to die away from the others and ignore them. She knows they are going to die from a heart defect or whatever and just doesn't waste her resources. It also isn't uncommon for a mother to eat her stillborns or dead pups. As gross as that seems for us, it is not cruel or gross to rats. It is a natural behavior practiced in the wild for many good reasons (so the smell of death doesn't attract predators, to get back lost energy, etc.).
There are "bad" mothers who will actually kill some of their litters to make them more manageable or because they have been handled by people, but these cases are much rarer for rats than other rodents. A stressed rat in a noisy environment may actually bite of legs or tails or even accidentally kill babies when she is trying to sever umbilical cords, because the babies squeaking is the only way she can tell her offspring from the placenta. (Remember rats can't see very well, and both things smell the same.)
Sometimes a rat can't produce enough milk for her litter. This problem is common to hairless rats but may also occur in other cases. You will be able to notice this by checking the litter every few hours to see if their bellies are white with milk. If some or all aren't, then you should start supplementing the babies or finding a foster.
The mom may have problems with the birth. She may start hemorrhaging, in which case you need to get her to the vet immediately. Rats can and do die from this. Also, babies may get stuck in the birth canal or have other unseen complications. If your rat is several days overdue or has had part of her litter and has stopped giving birth but is still in labor for a long time, you need to get her to the vet.
All that said, you shouldn't be paranoid because most of the time things do go smoothly, but you should always be prepared!
The original untainted meaning of culling is to pick only the best animals for breeding and make sure the other, less fit animals do not reproduce by neutering them or placing them as pets with contracts that they won't be bred. In this sense, culling is something breeders of any animal should practice...
HOWEVER, when rat breeders use the term "culling" or "thinning," they are usually talking about killing some of a litter to "make it more manageable." Many people believe (falsely) that a rat cannot handle more than 12 babies easily because she has only 12 teats. They may cull some of a litter because small litters thrive better. But, those claims are just myths. The truth is most moms can handle litters of 13, 15, or even 20 without any extra help. One of the fastest growing and healthiest litters I ever saw was a litter of fifteen raised by a first time mom without a foster. In other words, killing pups is not necessary. My point is, when people cull, they may be thinking about the mom or litter, but in reality, its only real purpose is to make it easier on the owner either in raising them or finding them homes. It makes even less sense if you are seeking to continue a certain line. If you cull some babies in the first week, how will you know you didn't kill the best typed or marked or colored animal? Most reputable breeders frown upon the practice, and if you cull they may not adopt from you. If you do choose to cull, you will have to look around the internet for how to go about doing it "humanely." I do not have any experience or knowledge in this except in knowing alternatives to it.
If a litter is very large and there are some runts emerging, you can help them along by taking out the larger pups and leaving the small ones with their mom for an extra feeding or two and providing the mom with extra protein and dairy in her diet to keep her energy yet. You may also choose to feed the pups kitten formula, human baby formula, or goat's milk in addition to their nursing. This is best done by allowing the babies to lick the milk from a towel or your fingers. Pups can choke or drown on an eye dropper or syringe.
If the mom dies or is not producing milk, the litter's best chance of survival is a fostering rat. There are several ways you can go about having a foster mom. One way is to breed your females two at a time. That way, a mom with a smaller litter may serve as foster for some of the babies in a larger litter and you will have a lactating female in case the other one dies or abandons her babies. You may instead just plan litters close together, so your next litter is born when a previous one has just been weaned. Another potential source of a foster rat is a nearby breeder. Try to develop a relationship with another breeder or breeders nearby. They may let a rat with a litter or one that has just weaned a litter serve as a foster for you or you may do the same for them. The last source of lactating females is in a pet store. This may be expensive because you may have to buy a rat and her whole litter; though the pet store owner may be sympathetic to your circumstances. Also, you'll have to be careful, as the new mom can't be quarantines and may bring diseases or parasites into your colony. Still, the pups have a much better chance of survival with her, so the risk is probably worth it.
If a foster rat cannot be found, you can try to raise the babies yourself. The older they are when hand-rearing begins, the better their chances are. Kitten formula or baby formula can be used to feed the litter. Most pups can lick formula from a towel or fingers at a week old or so. If the litter can't lick enough to be full, you will need to use an eyedropper or a syringe without a needle. If the mouth of the instrument is too wide, use small tubing to make a smaller one. Make sure none of the formula gets in the rats' noses and their noses don't bubble when they eat. Don't squeeze or force it. Just keep a drop of formula at the end of the dropper for the pup to drink. Feed them as much as they will eat every four hours. This may mean you have to set your alarm clock to wake in the middle of the night and find someone to take care of them when you are at work or school (or plan your litters for vacation months). Older babies do not need fed so often. The other thing s you will need to take over is cleaning the pups (particularly where the urinate/defacate) with a warm, wet towel. You will also need to keep pups warm until their fur comes in completely. A hot water bottle can be placed under the aquarium, but I wouldn't recommend a heat pad, because the babies could be overheated or burned. You should keep the air temperature of the room in the mid to high 70's (Fahrenheit). Pups can be fed some solid foods at two weeks old but will need the formula until they are at least three or four weeks old.
Litters vary as to how quickly they develop and how large the youngsters get. However, here are some milestones, you can watch for:
~Babies are born blind and naked. Sometimes, you can see pigment in dark ones at the very beginning, other times, they all look pink. Rats can be sexed at this age.
~In the first few days, the darker babies, such as black and chocolate, will start to show. By day 3 to 5, you will be able to make out some markings. Nothing specific, just if they are hooded or capped or solid. You still won't be able to tell a beige from an albino until their fur comes in.
~By the end of the first week, the litter has a fine velvet of fur on their backs. Their stomachs will still be bald, and Berkshire markings will be fairly indistinguishable. Their ears will also poke out a little, and you'll be able to pick out dumbos (which have downward-pointing ears). The color of lighter rats should be more obvious.
~In the next few days, their bellies should start to get fur. At this point, they are very easy to sex. Females have nipple spots, while males don't. They also start doing things that just look cute, like cleaning themselves and each other.
~Around 13 to 16 days old, the pups will open their eyes. Usually larger, more outgoing ones open them first. At this time, they will also start trying solid foods, so provide them with extra birdseed and other things. The mom will soon give up trying to keep the little buggers in the nest all the time. Generally babies will seek out their mother now. (I like to move my rats to a multi-level wire cage at this point.)
~After two weeks, the pups will just start looking and acting more and more like adults, wrestling, eating solid foods, drinking from a water bottle. By four to five weeks old, the pups will stop nursing completely.
~It is important to separate males from females as soon as they stop nursing. By five or six weeks, they are capable of reproducing with each other. It is best to keep them with their same-sex siblings until six weeks old, if possible, so they will get in all the lessons in socialization they'll need for adulthood.
A note on Megacolon
Megacolon is one of the worst and hardest to work with of the hereditary diseases. Although it is linked to certain markings, such as odd-eyes, blazes, and tricolors, it can appear in other lines too. The most obvious MC symptom is bloat, which shows in rats at three to six weeks old (shortly after they start eating primarily solid foods), and despite the best efforts to treat it, megacolon kills all affected rats at very young ages, usually before 8 weeks old. The steps you can take to avoid this is to just KNOW YOUR BREEDING RATS. Get pedigrees as far back as possible, and find an honest breeder who can tell you how many MC cases he/she has had and what rats produced MC babies. If you want to avoid it completely, don't breed odd-eyed or blazed, mostly white marked (not albino, that's a different gene) rats, or rats from lines associated with these types of markings or megacolon. Because of MC, these types of lines should be bred very catiously with a lot of knowledge and experience.
There are other forms of megacolon that set in later in life. These are less common. They are not a death sentence and can often be managed with diet and medication.
Tips for New Breeders
Thinking about becoming a breeder? Here is some advice, speaking from experience:
This section will focus on finding homes for your rats. Even if the litter was not your fault (such as you adopted a pet store rat who turned out pregnant), you may want to at least try to find good homes, before you leave the quality and length of their lives up to fate. (Keep in mind that nearly ALL of pet store rats end up as reptile food, and most shelters do not accept pocket pets.)
If you planned ahead of time, hopefully you have a few people who are already interested or even reserved your rats. Contact these people after you know the colors and genders of your litter, so they can let you know if they are still interested.
It is VERY important that you start seeking homes long before the litter is weaned (even before they are born is a good idea). There are homes out there somewhere, especially if you have carefully planned out and raised the litter for good colors and health and you have pedigrees. Let your family and friends know about the litter, and promote them to the particulars of your audience. For instance, in a college town, you may promote them as affectionate and low-maintenence apartment pets; while in a family neighborhood, point out their cleanliness and docile personality. Many people may be a little hesitant toward rats as pets, just because they are RATS. You can help improve this attitude, by taking your pets (not the mom or babies, though--it might be stressful) to a park or fair.
An excellent place to find homes is a rat show or pet expo. See if there are any near you! Consider joining a rat club or an e-group or posting on rat-related message boards. You'd be surprized at how many rat fanciers live within a couple of hours and would be willing to drive to get a hand-raised pet or two.
Some important things to do to find the rats a good home is to ask the adopter several questions, especially concerning care, experience with rats and other rodents, and children in the house. Asking for an adoption fee is also a good idea. You likely will not make back the money you put into raising them, but a fee shows a contract between you and the adopter and also shows the person (almost subliminally) that this animal is valuable and not a "disposable pet."
Remember not to breed unless you can care for the offspring yourself. Have some extra cages ready in case certain colors or a gender just can't find homes. If you find you have too many, DO NOT breed again. Try your best to find homes for ones you can't keep or enlist the help of a breeder or rescuer. Remember that breeding is not for everyone. Make your decisions wisely.