mother rat aggression

Question
QUESTION: I'm not sure if this is the right type of question for you, but I'l ask anyway. My rat, Salena, has been a great mother so far. She lets us hold the kits no problem and is taking great care of them. However, I recently brought home a new rat, Minca (I'm guessing she's around 2 months old?), from the petstore. She is a real sweetheart, not aggressive at all. When we first introduced her to Salena, they got along great. But when Salenas babies (4 weeks old) went in the cage near Minca Salena suddenly became very agitated. Minca was being nice to the kits. She was very interested in them but not acting aggressive. Anyway, Salena's fur got all puffed up and she started shoving Minca around. I looked it up and i think its called sidling. She was rubbing against Minca, shoving her head under her, crawling under her, acting really strange. They broke out in a little fight (not serious, no injuries) so I had to separate them.
After that Salena started getting aggressive with her other cagemate, Denali, who she has always been fine with. Denali is about 2 and Salena's lived with her all her life. They didn't fight but she was doing that same pushing thing. Denali just ran away. Then, later, when Minca was crawling around Salena's cage, Salena was lunging at her through the bars all puffed up. But she's still fine with us. Why is she doing this? When will her maternal aggression go away? The babies should be weaned about now but she's still nursing them regularly. Is this normal?

ANSWER: Hi Lindsey

Did you put the new rat in quarantine for 3 weeks before proper introductions to the existing rats?  THere are two deadly viruses going around pet stores that take up to three weeks to incubate so the new rat should be kept in another area for this time before introductions.
Also, did you introduce the new rat to the existing rats, placing their cages side by side for at least a week and allowing them to meet on neutral ground, or did you just put the new rat in with the new mother rat?  If so, this is why there are problems.  No rat is really going to appreciate a new rat they know nothing about, have not had the opportunity to smell her and get to know her for at least a week outside the cage and just put her in the rats home, especially when she has her precious cargo of babies. She indeed will be protective of them but it goes beyond motherly instinct. It is typical rat behavior to be upset at a strange rat being in her own cage. This causes serious territory issues and can cause aggression that may not be resolved easily now.

I am a bit worried about quarantine though since there are new babies involved and this new rat is a petco rat that may have carried something to the new rats. They may look perfectly fine and healthy but can be harboring SDA or Sendai virus that could wipe out all of the rats in the colony.

As for the babies being weaned, the mother is not going to wean them herself at this age.  It is up to you to do this. You should have the males out by the time they are 4 weeks old or they can get both mom and the baby females pregnant at any time. Have you sexed them yet?
Its up to you to wean them. As long as they are living with her they will want to nurse.  Do they eat solid foods yet? They should not be eating rat seeds but instead should be eating a lab block along with some soft veggies and some fruits. You can wet down the rodent block with warm water before offering it to the babies. They should have been taught to use the nipple of the water bottle too.
Do you know who the father is of the litter or did you bring the rat home pregnant?
Please let me know. It sounds like things may be a bit hectic.

For proper quarantine info please check here:

http://www.freewebs.com/crittercity/thequarantinepage.htm

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

QUESTION: We quarantined her for about a week and a half, I thought that would be long enough, since most petstore rats that die usually die pretty quickly. Its probably too late now but i could quarantine her longer if you think its necessary. I put her cage next to her for about 4 days, then opened both cages to allow the rats to come out and meet on mutual ground. Salena went into Minca's cage and they got along fine until one of the babies followed her in. As soon as the babies went in the cage with them Salena began to get aggressive. I know the father of the litter, he's my cousin's rat. The litter was planned and everythings going great. I didn't plan on bringing home a petco rat since I know how unhealthy they can be, but i saw this beautiful mink girl and couldn't stand the thought of her becoming a feeder rat. I know I should have quarantined her longer but she's really shy so I thought that by being around other rats she might get a little friendlier.
While doing research I read that mother rats will wean their babies by themselves around 4 weeks, and I thought the males could stay up to five weeks. ??? If i need to seperate them now thats not a problem since I have four cages, I just hate to tear them away from their mommy before I have to. I have known their gender for about 2 weeks now. I have 6 boys and 7 girls. They're eating solid food, they have been for a while. Things aren't too hectic. Spending the majority of my time cleaning cages and socializing and playing with 16 rats is exhausting, but things are going pretty smoothly. The babies will be going out to their new homes next weekend. I've already got people with reservations. I feel a little guilty for now quarantining Minca for longer, though.

Answer
Dont worry about the quarantine now or feel guilty. Now you know for next time. If you read on a site where it says 2 weeks, that means its 2weeks for ecto or endo parasites to hatch, but the viruses take up to 3 weeks to incubate.

As for weaning, mom will let them go much longer than just 4 weeks if the babies persist but taking her out of the cage even for a day works to wean.  What you can do is when the babies usually feed, make sure mom isnt in the cage at that time. Do this daily till they arent feeding. Mom will stop them when she feels her milk drying up and it will dry up the more feedings she misses.  As for males being fertile around 5 weeks, its the norm for it to be five weeks but the truth is, it can be as early as 4 and a half and its not worth the risk at all.

Since your first message wasnt clear in explaining that you let them meet prior to putting Minca with Salena and they had at least four days to get to know each other just through smelling (which tells alot, btw, from what sex the other rat is to the rats age and even if the rat is in eat!) the reason Salena was aggressive is she is being careful of her babies.

You have it pretty much down on what to do so keep up the good job.  I am sure it will work out just fine and the girls will all live together happily ever after once Salenas hormones even out again.