American Fancy Rat & Mouse Association

This article is from the WSSF 2009 AFRMA Rat & Mouse Tales news-magazine.

Breeding & Stuff

Huge Rats, ID for Rats, Mothers Eating Young

By Karen Robbins

Martin Clark, Australia, e-mail
Q I got your e-mail address off of the AFRMA web site and I was hoping that you could help me. I have bred a few rats and this time with two youngish females. One female had 5 young; within a week or so I could see I had 1 huge bub, 2 medium size, and 2 normal size. Unfortunately, the mum initially let the 2 small normal size ones die and fed the 3 others for a while, then she ignored the other 2 medium size ones and only fed the huge one which at 4½ weeks old is well on the way to being her size.

I have another female that has done the same—they were born within a couple of days of the ones I just described, 6 born 3 left. They’re what I called the medium size before. The rat I wrote about in the first paragraph is now 6 weeks old and almost the size of the mother. I’m sure that this must have happened before elsewhere. What has happened? Is it possible to breed these with the other one that is the same and get a strain of “Fast growing rats”? I did lose 4 others to get this one.

Is there a book I can buy about breeding rats and which one do you recommend?

Also, what is the best way to identify individual rats? As a teenager I used to breed birds, and I bought numbered rings that would go on their feet when they were young and by the time they were old enough to leave the nest, the ring was impossible to take off. Obviously this won’t work on rat’s feet.

And another question for you: When the females become pregnant I put them into a tray on their own, they have clean water, plenty of food, and the bedding is changed regularly.

My problem’s are:

  1. I have a mother that has had babies before and she has eaten the whole litter this time.
  2. I have a young mum, she got pregnant accidentally and she is about three-quarter adult size, I just found her covered in blood on her hind legs and some on her belly.

Do you have any ideas why?

A If mom is small and she had lots of milk for only one baby and if it is a male, then yes, it could be almost the size of mom at 6 weeks. It sounds like there might have been something wrong with the ones she didn’t feed and then died.

If they are indeed huge rats (some breeders refer to huge rats as Jumbo), then you could work on a line of rats that get larger than normal. Of course diet also plays a role in how big/fast growing a rat will be but you don’t want them to become obese when they are adults or you will not get the females to breed.

How much do they weigh in ounces and grams??? One breeder’s guideline is 6 week females should be 6 oz, males 8 oz, and 4 month females should be 11 ounces for normal size rats, otherwise they are too small/fine boned to be bred. We have an article on weights for pregnant females and babies up to 3 weeks

AFRMA has a Breeding book that goes into just about everything. I don’t know if any of your Australian clubs have anything. Some of the basic pet books may have a chapter on basic breeding.

As far as ways to tell rats apart, we have an article giving several suggestions Another way of permanent ID would be to tattoo an ID spot or number into their tail (like tattooing show rabbits in their ears or goats in their ears/tails). Laboratories sometimes notch their ears but we don’t recommend that. I’ve heard of using the leg bands made for rodents on their hind legs but you have to make sure they grow with the animal or change them as they grow. Most people just keep different colors/types together so they are all mixed in each cage.

Regarding mothers eating their babies: Environment changes—too hot, strange noises, strange animals, etc., can be a factor—though this happens more with mice. Moms should be individually placed in solid bottom cages with no levels such as a 10–15 gal aquarium or other type of container. Sometimes cleaning the cage/moving the mom during delivery can upset her. Babies can sometimes be injured during a difficult delivery or if there are other females in the cage and they each try and move the litter to “their” corner or two females will use a baby for tug-of-war with each one trying to move it to their area. Some beddings can be fatal to baby rats. Did the one that ate her babies have the same father for this litter as her other one?

We would need to know the age of the one that got pregnant accidentally and if she was with any other rats at the time to give a better answer. *

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Updated February 17, 2014