# Breeding for size



## Gracegarden

It seems proper show mice can be hard to come by for isolated, new or 'less talkative' breeders, therefore some of us may be left trying to breed size into pet type mice.

Can some suggestions please be posted on how to do so?

So far the plan seems to be using the largest offspring from each litter. This seems like it would take an eternity. What are the options I am missing?

If this is the case; should we select for size first and then over time decorate the body?


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## Gracegarden

One more question...

If we are out-crossing for size, does it matter if we choose a large buck or a large doe? Is one better than the other?


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## Fraction

If you're trying to make 'show type' sized mice out of pet shop stock, then yes it's going to take a while! Breeding largest to largest (whilst keeping an eye on ear/eye/tail size if that's important to you, too) is your best, and I think only, option.

For an outcross, I would breed a larger doe with a smaller buck. If you breed a larger buck with a smaller doe, it could possibly be uncomfortable for the doe if her babies all take their father's genes for size. I'm not an expert though.


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## candycorn

I think you will find that saving up for a while (even a year if you need to) to pay for a road trip to pick up good large mice would be far easier and less frustrating that trying to take many generations to get there. But it is of course possible. It just takes a long time.


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## Gracegarden

Thank you, both.


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## Jack Garcia

You can't equate type and size, anyway (it's unclear if you were doing that, so I'm just pointing this out).

There are typey mice who are small, and giant mice with poor type (believe me, I've owned a couple!)...

You have to remember that it's taken 150 years to get our mice to where they are now, so if you decide to work with only pet store mice it's reasonable to expect it to take that long because in essence you're "starting over."


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## MojoMouse

In relation to size, I suspect it's better to have a gradual increase over many generations rather than trying to fast track if you're starting with pet type mice. My reasons for saying this is that the increase of a mouse's size should be proportional. I imagine it's possible to fast track skeletal and muscular size, but the organs of the mouse need to keep up. (I'm not a biologist so I'm just theorising here, and would be happy to stand corrected if I'm off track here.) One of the main organs that could struggle with the size increase is the heart. I'm not sure it would get larger at the same rate as the mouse's frame. If this is the case, you'd end up with show sized mice, but they'd have reduced longevity compared with the show mice that have been developed gradually over more than a century.

Getting some show stock would be the way to go if this is possible for you, as candycorn suggested.


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## moustress

I had asked some time ago if anyone knew about the internal anatomy of show meeces; is their heart proportionally bigger to match the size of the body? And what about the other organs, esp. lungs, kidneys?

Gracegarden: Breeding for size can be a lesson in frustration, take it from moi. Recently, though, five or six breeders fanning from Arizona to Mayland have collaborated and imported a few dozen show type meeces into the US. In a half a year, one may be able to acquire some of the offspring of these lovelies. It takes years to see a difference in size, even with meeces like mine that have a bit of show mousie blood in them. I don't breed for show, so it hasn't been a top priority for me. Besides which, I think type in proportion is more important than just size alone.

I do wonder if bigger meeces are healthier than smaller ones.


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## MojoMouse

I'm not sure about every aspect of health, but I suspect the smaller mice have greater longevity. I agree with you about type in proportion being important.


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## Jack Garcia

MojoMouse said:


> I'm not sure about every aspect of health, but I suspect the smaller mice have greater longevity. I agree with you about type in proportion being important.


Anecdotally, this is probably true. Smaller animals of the same species live longer because they need to consume and expend fewer calories, and have fewer (or smaller) cells in which illnesses such as cancer can occur. Look at the varying dog breeds--small breeds live longer than larger ones--for a clear example. Aubrey de Grey has a lot to say about the subject in humans.


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## Autumn2005

In horse breeding, we know that the dam contributes to 80% of the size of the foal... In general, the bigger the mom, it seems the more room the babies have to grow, so always go for the biggest girl.


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## tinyhartmouseries

If you are only breeding for size, it's actually pretty simple. Breed your largest to your largest and cull litters down. When I was breeding pet type piebald mice, once I bred a buck who had a body 1" longer than his father's. Even now, my pet types are as large as my show types, some larger. Some of it is luck too, but one can't go wrong breeding biggest to biggest if you are only increasing size.


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## sys15

are you breeding to have larger mice now? or to breed a genetically larger line of mice? if the latter, maternal effects and culling the litters to a small size will contribute little (although they may help you select more precisely among siblings).

personally, i'm not sure i'd want to breed mice terribly large. and incidentally, many of my pet store line mice are larger than my recent english imports.


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## MojoMouse

With mice ideals, in a country that doesn't have show types, there is more room for personal preference. Personally, the largest size possible has never been a priority for me. Needless to say, I don't breed puny, runty mice, and only select mice that are well developed. But the specific choices I make are based on other traits. I'd be thrilled to have mice that have show type features, but not necesarily the size. I suppose it's got a lot to do with what you get used to. UK and US breeders, (or at least the ones in the showing community) are just used to big sized mice, and have had their preferences shaped by these norms.


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## Jack Garcia

If you imported blacks or black tans, that's why. They're naturally smaller varieties. I have some agouti tans who I think are probably bigger than the black tans (though without seeing them side-by-side I wouldn't know).

I do obviously like large mice with excellent type, but part of what makes them mice is the fact that they're smaller than most similar animals. If mice were the size of large rats (or chihuahuas) I don't think I'd breed them.


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## sys15

Jack Garcia said:


> If you imported blacks or black tans, that's why. They're naturally smaller varieties. I have some agouti tans who I think are probably bigger than the black tans (though without seeing them side-by-side I wouldn't know).
> 
> I do obviously like large mice with excellent type, but part of what makes them mice is the fact that they're smaller than most similar animals. If mice were the size of large rats (or chihuahuas) I don't think I'd breed them.


i agree (regarding rat-sized mice). the smallest of my imported mice is the black tan male. to me, he is about the perfect size. most of the largest mice from my pet store stock are agouti.


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## MojoMouse

Why are blacks smaller? Is it that the breeders over the years have selected for colour rather than size (unlike PEWs, where colour is not really an issue) or is it because there's something genetically different about them?


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## Jack Garcia

Probably both, although I couldn't link you to any studies. Lighter animals in general have potential to get larger. It's controversial to mention, but look at people: as a whole the palest are also the tallest (Scandinavians), and the darkest are also the smallest (African pygmies). It doesn't always hold true, of course, but when you're speaking broadly, it does.


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## moustress

I'm wondering the presence of black pigment inhibits growth, somehow.


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## Cordane

I know in cows it does, I have mentioned this before but in highlands, black animals mature slower though there is a reason. They were bred in an area that had very little grass so they ate less and took longer to gain weight and grow than other colours.


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## Gracegarden

This has been some interesting dialog. I need to do a lot more thinking.

What started me thinking on the size question is that AFRMA standard mentions, "...but all other things being equal, the larger animal shall have the advantage."


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## Jack Garcia

In case you've never had show mice, this is an example of a show mouse next to a pet store mouse.

As you can see, the size is different, but so is the way the body is built:










(PEW mouse owned by Jenny, pet store brindle bred by me and owned by Robin, both photographed by me at an ECMA show in 2008, handled by Kadee)

In particular notice the differences in tail, haunches, head, and ears.

What a lot of people call "show mice" aren't particularly good examples (although they could be shown in many clubs), but I like this picture because it is. Jenny's PEW is a good example of a show PEW, and my pet store brindle is a typical (I can't bring myself to say "good") example of a pet store brindle.


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## MojoMouse

Wow! that pic certainly highlights the differences. The importance of breeding for all aspects of type together, rather than just size, is highlighted. My feeling is that if that brindle was as large as the show mouse, but without the racy body type and other distinct features, it wouldn't be a very aesthetic animal.


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## Seafolly

:shock:

I had no idea. I've had super tiny rats from the SPCA weigh in at ~150g at their "normal" weight and it looks like that one wouldn't be toooo far off?


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## Jack Garcia

Um...probably about that much, maybe a little less. I've never really weighed mice.

Large mice with good type don't actually weigh as much as you might think, though...they have a different feel in your hands, because their musculature is so well-developed (you can see this mouse's muscles), and their fur is very short and very close to their skin, so they feel more "solid" than heavy. This is not really as true for pet store mice (or some "show mice"), so if you're holding one in each hand you can tell the difference between a well-bred animal and a pet store animal just from how they feel.


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## candycorn

I would truly love to have a mouse like that one. That is what I will try to import one day!


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## MojoMouse

Jack, do you have a pick of a super sized light coloured mouse next to a black (or dark mouse)? It would be interesting to see the proportional difference in size.


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## Jack Garcia

Not off-hand, I don't think...


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## Stina

I don't know if it would make that great of a difference in such a small species though...


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## Jack Garcia

That's true.

I've always wondered how tiny dwarf mice (à la dwarf rats) would be and what they'd look like...


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## Stina

There are dwarf mice.


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## Jack Garcia

Where?


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## Jack Garcia

Never mind, I was able to answer my own question, and it's pretty interesting! Look:

http://johnbarban.com/life-extension-li ... d-smaller/


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## MojoMouse

Jack Garcia said:


> Never mind, I was able to answer my own question, and it's pretty interesting! Look:
> 
> http://johnbarban.com/life-extension-li ... d-smaller/


Light, human interest piece, but so interesting! 

With your academic contacts and access to research, would it be possible to dig up some more info on this? I continually run into brick walls due to 1. My lack of association with academic institutions, and 2. My limited capacity to fully understand some of the detail in pure research articles.

I have a personal vested interest in the topic. I'm 158 cm, weigh 42 kgs on a big day. I don't have dwarfism - I just don't get a good view when I'm in a crowd... however - I plan on living forever - so far so good! 

I also have quite a few smallish mice. Not runts, just small. They also have visions of long fruitful and rewarding lives.


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## SarahY

> It seems proper show mice can be hard to come by for isolated, new or 'less talkative' breeders, therefore some of us may be left trying to breed size into pet type mice.
> 
> Can some suggestions please be posted on how to do so?
> 
> So far the plan seems to be using the largest offspring from each litter. This seems like it would take an eternity. What are the options I am missing?


Cull your litters as early as possible using skull size as a guide. The pinkies with the wider heads across the muzzle and between the ears will be the biggest adult mice. Discard any pinkies with narrow heads and whisker beds, these won't have the bone that you need in your breeding mice. Also look at how fat the tails are, again this indicates heavier bone. Then when choosing adults to breed don't go by weight, go by length and breadth of head. A fat, heavy mouse could have smaller bone and length than a longer, lighter mouse. It will take a very long time, but you will see definite improvement within a couple of years.



> If we are out-crossing for size, does it matter if we choose a large buck or a large doe? Is one better than the other?


Always, always use a larger doe. They have more resources in their bodies to feed their kittens. While a bigger, typier buck may produce kittens with better type, a small doe will not be able to help them reach their potential for size.



> I had asked some time ago if anyone knew about the internal anatomy of show meeces; is their heart proportionally bigger to match the size of the body? And what about the other organs, esp. lungs, kidneys?


Well, after feeding mice to my harris hawk for a while now I can tell you that bigger mice do indeed have larger organs. I get to see the organs a lot now.



> Why are blacks smaller? Is it that the breeders over the years have selected for colour rather than size (unlike PEWs, where colour is not really an issue) or is it because there's something genetically different about them?


I've noticed that pigment concentration weakens the type and size. When I was breeding doves, the paler silvers always had superior type and size to the doves. You can get blacks the size of PEWs, but their colour is weak and the flesh pigment much less than on a good quality show black.


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## Jack Garcia

MojoMouse said:


> With your academic contacts and access to research, would it be possible to dig up some more info on this? I continually run into brick walls due to 1. My lack of association with academic institutions, and 2. My limited capacity to fully understand some of the detail in pure research articles.


Yes, but it's summer and I'm preparing to leave town. I can't go to the university libraries any time in the next couple of weeks. Well, I might be able to Thursday. We'll see. My remote access (from home) is more limited in the summer.



> I have a personal vested interest in the topic. I'm 158 cm, weigh 42 kgs on a big day. I don't have dwarfism - I just don't get a good view when I'm in a crowd... however - I plan on living forever - so far so good!


I'm...significantly larger. When I called myself an ogre, I wasn't joking. 



> When I was breeding doves, the paler silvers always had superior type and size to the doves.


Part of this is optical illusion. On the same background (i.e. your coffee table or the show bench), two things of the same size will always appear slightly different so long as they're different color depths. For example, if you cut two identical plastic circles out to the millionth of a millimeter and put them side-by-side, the lighter one would appear slightly larger.

For example, this:










...which is #3 on this page: http://www.jimloy.com/puzz/illusion.htm (also see #15)

You always have to take this into account.

I know some fanciers in California who have actually measured the skulls and ears of mice after they died to find that often mice who appeared larger (and were lighter) weren't necessarily when their measurements were taken. This affects type, too, because larger, broader heads are favored but they might _appear_ to show up more commonly on PEWs than doves (for example) when that may or may not be the case...it's a small difference but a real difference. And when your subject is moving around, that complicates things a bit more!


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## Gracegarden

SarahY - that is such helpful information, thank you for making it so understandable!


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## Shadowrunner

I think I might have a theory for you too. It's a bit long though.

The science channel did a program on race and the reasons for why people would need pale skin in northern climates.
While people nearer to the equator needed darker skin.
The Idea is that at the equator, Uv rays become a problem, destroying DNA, making cancer more likely and messing with your folate levels. Folate being very important in embryo development. So people with darker skin could survive longer than those who weren't protected, and reproduce more successfully.
But since there was so much Uv light there, they didn't have a problem with producing enough vitamin D, which helps you use the calcium you ingest.

But at higher latitudes, the UV light is less. So people who were darker, could not make enough vitamin D, which would mean bones would be more frail or
deformed. Think about how fast embryos develop, they need calcium too. So if you lived somewhere more northern, it would make sense to be paler so as to let in more light. And since there isn't a ton of it flying around there, it wouldn't be as big or immediate of a threat as a calcium deficiency.

So if darker people in more northern places (or don't get enough sunlight) 
They can have issues with reproduction and growing themselves.
Would the same thing not apply to mice? 
Assuming their diet lacked enough vitamin D to keep them healthy?

It's just and Idea really.

I don't know who told me to do it, but I look at the heads of newborns when choosing for size.
Wider skulls more often belong to babies who will be bigger.
Smaller litters tend to have bigger individuals as well.


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