American Fancy Rat & Mouse Association

This article is from the WSSF 2010 AFRMA Rat & Mouse Tales news-magazine.

Breeding & Stuff

Breeding Ages & Weights of Rats

By Karen Robbins

Michaela Laciková, ZOCHDH-LP, Slovakia
Q Could you tell me please, what are your accepted standards for the lowest and highest age and weight of male and female to be used for breeding? I ask because I am concerned that Slovak standard is too benevolent in this so I would like to compare it with your limits.

A We don’t really have any set standards in AFRMA for breeding ages; however, most breeders breed their females for the first time at 6 months. If the female is of good size and weight, then 4 months is fine. There are some lines of rats you have to breed the females at 3–4 months or you won’t get anything if you wait too long. Another example of breeding early would be if it was necessary to continue a line due to your male being elderly. Three+ months would be the soonest and that would only be if they have good size and weight on them, but 4 months minimum would be better. We do have one page online with a similar question regarding breeding age for the first litter

In regards to the maximum age to breed a female, I would say until she no longer breeds which can be anywhere from 8–10 months to a year and a half or so, especially if she does not have problems with the litters, is a good mom, produces some very nice kids, keeps good weight on during the raising of the kids, has lots of milk for the kids so they are not too thin or small for their ages, and as long as she has sufficient time in between litters to recuperate. Some breeders only breed their females once, others will get 3–4 litters out of them.

As far as the males, personally I don’t recommend breeding them before the 6–8 month age so you make sure they aren’t going to develop any hormone (aggression) issues. That way if any issues develop, you won’t have produced babies that you have to tell the new owners they may potentially have problems with their rats and they should not be bred from if sold to breeders (hormone issues are genetic and rats that have this problem should never be bred—it can skip a generation so people should not think that one generation was fine and continue to breed these types of rats; it can be passed from both male and female—“Neutering and Aggression” question in the online page Also, breeding a male too young could emotionally damage him (he would become afraid of females and not want to have anything to do with them) if he is placed with an “aggressive” female that would need a male that knows what he is doing. One breeder found when she bred a male very young he became very aggressive—“Breeding Age Of Male Rats” question on the online page I usually don’t start breeding my males until around a year of age but that is because I want to use my males to their maximum benefit on the colony before starting to use a younger male that would replace them. Again, on the maximum age to use a male, it would be until he no longer produces or is too old.

We do have guidelines we recently came up with as far as weight on what they should be: 6 week females should be 6 oz [~177 g], males 8 oz [~236 g], and 4 month females should be 11 ounces [~311 g] for normal size rats, otherwise they are too small/fine boned to be bred. As long as the rats aren’t fat, then there wouldn’t be a maximum weight for breeding.

And of course good health and temperaments are expected of your breeding stock.

Hope this helps! *

Updated February 18, 2014