Breeding Information, page 1
One person can make a difference,
but it's up to the individual what type of impact they will have.
Once you've decided to breed, you need to decide which rats to mate. First, it's very important to start with rats from other breeders and to really know what is in their pedigree. If you breed pet shop rats, you'll have no idea about the kinds of genetic problems that they're carrying. You'll want to question these breeders about things such as the line's resistance to myco (it should be very, very high because their level of resistance will be passed on to their offspring), any instances of tumors (there should be none), is there any megacolon in the line (there should be none), bumblefoot (again, none), how long do most of the rats in each line live (should be AT LEAST 2 years, 2 1/2 to 3 years or beyond is much better), has there been any aggression in the line (especially when the males hit puberty at 6 months to 1 year of age), is there any nervousness in the line. You should only mate rats that have wonderful temperaments. Aggressive rats should not be bred because aggression can be passed on to their babies. Skittish rats can also pass their nervousness onto their babies.
These are some of the things that you'll need to take into consideration when you're choosing your mating pair. Healthy, friendly rats from healthy, friendly lines will pass these traits onto their offspring, likewise with unhealthy, unfriendly rats. Health, temperament and life span should be your top concerns. It's easy to breed in colors and markings, so it's much more important to start with a solid line and work from there. You will also need to take into consideration the fact that you will need to breed from unrelated lines, so this will mean going to several different reputable breeders. There is sometimes a bit of travel involved with developing solid lines. If you take the time to question the breeders that you choose, and if you're very choosy about the rats that you select for breeding, you will end up contributing to the health and future of the fancy, instead of polluting it like many haphazard breeders do.
More information to consider before breeding:
Breeding: Can YOU Live With It? by Mary Ann Isaksen
Should I Breed My Rats? by Gabriel Edson
Once you have chosen friendly, healthy rats, and built a solid line, then you can start working in colors and markings. This site has a genetics engine that will help you determine what colors you should get:
Keep in mind that an average litter is 10 to 12 babies, but they can deliver as many as 23. You need to be prepared to find homes for these babies, unless you intend to keep them all. The best age to breed a doe for the first time is around 8 months of age. This will give you some time to evaluate her health and temperament. It is a myth that, if not bred for the first time before the age of 7 or 8 months, their pelvic bones will have fused together and they won't be able to birth the babies. It is then safe to breed her again until she reaches approximately 18 months of age. Be sure to give your doe at least a couple of months after she has weaned her babies before mating her again. Does go into heat every 4 to 5 days. Sometimes you can tell when a doe is in heat because she may arch her back when you touch her rump or vibrate her ears. Many times, it is impossible to tell when a doe is in heat. There are different mating methods. Some choose to have the doe and buck live together through 2 heat cycles. I prefer to put the doe and buck together for the night for 7 consecutive nights. Does usually go into heat in the evening and throughout the night. If you leave the doe and buck with their cage mates through the day and only put the two together for the night, you won't have to reintroduce each back into their colony at the end of the mating process. When a doe is in heat, the buck will mate with her many times during the night. Each mating lasts only seconds, but not every one is successful. A male will usually sniff the doe or lick her and then he will grab the back of her neck and mount her. The doe will arch her back to allow the buck to mate with her. It is very difficult to tell whether or not a doe is actually pregnant until a few days before she delivers, however, if the doe and buck have been together for 7 consecutive nights, you can assume that she is pregnant. If the doe should become aggressive and start to fight with the male, you will need to separate them. You can assume that she is not in heat and try again the next evening.
Page 2: Gestation, Labor, Delivery, Postpartum, & Sexing