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Pet Rats/My 7 week old rat killed my 3 week old rat


QUESTION: I have a 7 week old male rat. I had a three week old male, too. Well, during the introduction my seven week old visiously attacked the three week old and killed him. I was trying to give him a mate and well, clearly that didn't work in my favor.

Should I even try to give him a friend at this point? He's seven weeks old! How the Hell did he murder my three week old with me right there!

Both rats had their own living spaces, too!

This was literally the introduction and the entire thing happened in less then 20 seconds and now I have to bury my baby.

What should I do? Do I get my male a mate? I cannot go through this again.

Should I fear for him and his behavior? He's perfectly fine with me, but all this happened today and I'm not sure what the future will hold. I don't want to bury another rat but I don't want my seven week old to suffer from Depression.

The baby was perfectly healthy , too. He was 100% fine and then the attack happened, 12 hours later, I'm holding a dying baby.

I buy rat pups because I like to raise them. I never had a problem with my femals in the past, but having males has thrown me into a depressive state. The baby was FINE and 12 hours later, dead. I believe Tou punctured his lung. He threw him on his back and bit him so hard that when I picked up Tofu the baby was hanging from his mouth.

I want to give him a friend and I will buy another pup (I want to say they're around three weeks because the males don't have visible parts just yet) but what should I do? How long should I wait? Will Tofu even be capable having living with a mate? I got him as a pup on May 4, and it's nearly June 4 and he's already killed a baby.

I'm so worried. So confused. So lost. I feel guilty and I hate myself for being the cause of a death. I haven't cried this hard in so long.

Please help!


ANSWER: Sarah-

Thank you very much for your question. First off, let me offer my condolences in the loss of your baby rat. :(

I would not hold the death of the baby against your older male. A three week old rat should not have been separated from its mother to begin with. A rat should remain with its mother for at least 4.5 weeks- that's the bare minimum. Even at that age, you can totally raise them to bond strongly with you. I do not think its worth the risk to jeopardize the health or safety of taking baby rats any younger than this. Even though your older rat is only 7 weeks old, he is much stronger than a 3 week old. The attack might have very well been an attempt to play-fight, but with the opponent being too young and weak in comparison.

I would say there is no problem getting your rat a new companion. You might want to get one that a bit older or at least the same age as the rat you have now. If you decide to go younger, remember to keep it around 4 1/2 to 5 weeks. You might want to also start the introduction in a neutral space, one that the older rat is not familiar with and therefore does not need to 'defend what's his' with the newcomer. Many people make the mistake of putting a new rat in the same cage with their older rats, thinking that just because they are standing right them observing that there wont be an issue. This most often makes matters worse.

I like to bathe my rats first, before putting them together in the neutral area (in my case, the shower). The rats spend most of the time grooming themselves that they pay little to no attention to the new rat. And if you use the same shampoo on them, they smell alike, making the newcomer more accepted.

If you are still worried about your older rat being too aggressive during the introduction, try putting your newcomer in a small cage inside the neutral area so that your older rat can smell and observe him without being able to get too close.

I hope that helps!

---------- FOLLOW-UP ----------

QUESTION: Thank you so much for responding and your advise.

I do buy my rats from a feed store, so their either pups or large rats, if I do get another pup, how long should I wait until the first introduction?

I really appreciate your kindness and advise. I'm just very much shaken up by this experience and feel so terrible. Should I even consider getting Tofu a mate or would he be okay to live alone?

Thank you once again


I would be sure to quarantine any new rats, regardless of age, for a minimum of 2 weeks, ESPECIALLY if they come from a feed store. Feed stores get their rats from the equivalent of a puppy mill. They don't have any regard to the health of their animals since they are being bred to be eaten and they certainly don't have any records being kept about the rats they do breed to guarantee anything on their health.

With quarantine, if they are carriers of any diseases such as Sendai and SDA infections, both very contagious, you would be able to spot them before transmitting it to your other rats. While quarantine SIGNIFICANTLY reduces risk of infection, it does not completely eliminate the risk.

An excellent article to read on these diseases and quarantining rats can be found on the Rat & Mouse Club of America's site.

So an answer to your question would be to wait at least 2 weeks before introducing any new rats to your others.

Rats do best with cage mates but there is the rare case of a rat that is unaccepting of any other rats. These, in my observations, tend to be rats that did not have proper socialization as young rats. I recommend all rat owners who are looking to add to their group, to always hope for the best, and plan for the worst- meaning to have full intention of joining the rats together in one communal cage and at the very worst, having adequate separate long term housing available in case they must be kept separate.  

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Shawna Laufer


Nutrition has always been an interest of mine as well as creating stimulating environments for rats. I conduct product reviews on my blog so I can take questions regarding products marketed or intended for rats. Other questions regarding basic husbandry, feeding, grooming, and other pet rat care will be accepted. I have very little breeding experience so I would not be able to answer much in the ways of breeding or genetics questions. I can help with some basic health care questions but am not a vet and always suggest contacting your vet for serious inquires.


I have over 13 years of experience with pet rats, having worked in several pet stores, as a veterinary tech assistant, and with my own pet rats. I run a highly regarded blog on the subject of pet rat ownership ( with a corresponding YouTube channel and Facebook page. I have been and always will be open to questions and comments.

A photograph of my lady rat's cage is being published in Worth Publishers' college textbook "How Children Develop, 4e" by Robert Siegler, Judy DeLoache and Nancy Eisenberg on the subject of how complex, stimulating environments and how they relate to the brains of rats.

I have some college experience, but not in the field of animals. I completed the majority of an at-home Veterinary Technician course which I was unable to complete due to financial reason. The majority of my knowledge on rats have come from personal experience, conducting my own research with the help of published medical studies and journal, the internet and through other knowledgeable 'rat people'.

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