Weaning Mice and Breeding Females

[Jay_Bunny]

The litter of mice I have right now is 3 weeks old today. I'm feeding some of them off today. They are around 12g in weight. I'm only keeping four females from this litter to raise as future breeders. I was planning to pull them at 4 weeks old but might pull them sooner as they are already eating solid food and not really nursing from the moms anymore. The two breeding females are around 40g each (having been well over 50g each when pregnant). I do like to give my females a break between litters but I'm wondering how long to give them since I'm feeding off all but 4 of their litter. They raised 12 babies between them (was 19 but 7 were killed - first litters)

[GoingPostal]

I give mine a 2 week break between litters and separate at 4 weeks or a little younger.

[kc261]

I keep mine in colonies with the male always present, so they are more or less constantly pregnant, and usually are ready to give birth about when the last litter is ready to wean. The females still seem healthy with good body weight, and give birth to good sized, quick growing litters. I figure they are designed to be able to handle it, otherwise they would not come into heat so soon after giving birth. There are species (humans included, although somewhat variably) where the females can't get pregnant for a while after giving birth because they don't start going through their cycle right away. The fact that they can get pregnant immediately after giving birth and while nursing a litter tells me their bodies can handle it.

So, even if you put them with a male again as soon as you wean the babies, they are already having a break of sorts.

[Jay_Bunny]

I am definitely in need of a bigger colony as soon as I can get it and the only way I'm going to get more females is to breed for them (and then purchase males to add new blood to the colony). I already have one breeding group that is 1.3, one of the females looks visibly pregnant (or she's just fat) and I also have a pregnant rat. So I really need to get this colony going. I was thinking of pulling the 3 week old mice and go ahead and put the breeding females in with a male.

[tomfromtheshade]

If you are in need of a bigger colony I would hold back all of the females that show good physical traits. Obviously, you won't hold back any females that display any abnormalities.

As far as buying new males to put into your colony I wouldn't do it. I would just use males that you breed yourself. I have learned first hand that if you only keep back the best of the best you are actually improving the animals in your colony. When you add new blood sometimes you run the risk of bringing garbage genetics into your colony.

I would just get your racks set up and start filling them with the best of the best females. Then you will have a great colony in no time at all.

Lets say that you have four females running right now. Lets say that they have 48 babies. Half of those are females. So, you have 24 females. Now lets say that only half of those females are animals that you want to add to your colony. Now you have effectively quadrupled the size of your colony in only about 90 days. It grows exponentially from there.

[Jay_Bunny]

I worry about inbreeding though. Won't that affect the health of my colony if I keep breeding related animals? I was always told to introduce fresh blood into the colony to keep it healthy. I ended feeding off some of the females I was holding back. I held back 4. The two does are back in with a male and I am waiting on 1-2 females to pop.

I don't have any racks right now because I just suck at building them. If I had a mouse rack that would make life so much easier. I have started building mouse tubs though. That way I can just stack them on top of each other as I build more. Once I move though I'm going to find someone to build me some rodent racks so I can really build up my colony.

I just did some math and I need 20 adult mice per week. How many females should I have in the breeding colony? And I need 9 rat weans and 8 small rats per week as well.

[chromeitout]

Don't worry so much about inbreeding for a few generations. I am on my 4th generation line bred and am just now looking to add new blood. When you think about how long a generation lasts (6 months) it will be a while before you need to worry about it.

Also, I never break up a colony for birthing or any other reason. If I lose a male in a colony then I'll grow out a male from one of their litters, and if this is not possible then I'll cull the whole group and replace them. Too many aggression issues when splitting up and reintroducing mouse colonies (rats are different).

As for how many... like I said I never separate my mice so to make sure I have 20 adult mice per week I'd have 5 groups of 1.3. Sounds like more than you'd need, but they don't always produce what and when you think they should, plus this gives you some hold backs in case a group goes bad. After a group is about 4-5 months old start holding back to replace them.

I'll let someone else comment on the rats.