Instructions
Choose the parents. When breeding for a certain trait like size it's always a good idea to choose parents who possess this trait. If you get your rats from a breeder who knows their stock, they can tell you if a large size runs in the bloodlines. Female rats are generally fertile between three and 18 months of age. As they approach 18 months and menopause, their fertility and the size of their litters will wane. Males are fertile between four and 24 months of age. Both parents should be in good health and not overweight.
Separate the doe from any other rats. If you keep several does together in a cage you'll need to keep the pregnant does separate as they can become aggressive and hormonal from their pregnancy.
Watch for signs that the doe is in heat. Some does will run around their cage, arch their backs, buck and wiggle their ears when they are in heat. When you notice these signs, put the buck in the doe's cage overnight. If she does not kindle right away, you may have to do this more than once. Sometimes the doe will develop a whitish mucus plug around her urethra opening when she has been impregnated.
Avoid handling the doe while she is pregnant. Keep feeding the doe her regular amount of food and avoid any stress to her. Handling and stress could cause her to reabsorb the embryos.
Allow nature take its course, unless you notice signs of severe distress. Gestation for most does is between 21 and 24 days. Complications during birth are rare and interfering with the birthing process is more likely to cause issues than help. Only when you notice severe distress or excessive bleeding may the doe need immediate veterinary intervention.
Give the new mother her regular food and water, plus soft, easy-to-digest food like porridge.
Handle the kits regularly. Handling the kittens every day helps them adjust to the touch and smell of human beings and prevents stress from handling later in life.
Wean and remove the kittens from their mother between four and five weeks after birth. Rats grow quickly and the mother usually stops feeding her kits at four weeks naturally. You can leave them in for a few more days or a week just to ensure the runts have had a full opportunity to receive milk from their mother.
Wait at least 6 weeks before breeding your doe again. Does should be in good physical condition before being bred again. Allow them at least six weeks post weaning to regain their strength and some weight before breeding them again. If after six weeks the doe is still not in top physical condition, it is better to wait longer for her and the next litter of kits' health
How to Breed Big Rats
Selecting and breeding for certain traits, including size, is not always an easy endeavor and it may take several generations before a trait appears fairly consistently through a bloodline. Even still, some animals may deviate from the expected genetic traits as recessive genes appear. Breeding large rats is easier than many other animals because their quick growth to maturity and short gestational period allows for a number of generations to be produced in a relatively short period of time.