Problem with mouse colony (pictures)

Recently I have been having a problem with some of my older breeder mice. I have noticed one male, and two females, from my four 1.2 breeding groups, have tumors. The two females are completely unrelated, and not in the same group
Male:
http://i247.photobucket.com/albums/g...s/IMG_0555.jpg
Females:
http://i247.photobucket.com/albums/g...s/IMG_0559.jpg
http://i247.photobucket.com/albums/g...s/IMG_0558.jpg
http://i247.photobucket.com/albums/g...s/IMG_0552.jpg
Also, all the females in three of my groups have these sores on their bellies. All are nursing, but I don't think that is what it is from. My younger trio doesn't have this problem.
http://i247.photobucket.com/albums/g...s/IMG_0556.jpg
http://i247.photobucket.com/albums/g...s/IMG_0551.jpg
These issues all showed up just in the last month. The only change that has been made is i switched all my feeders over to Purina's Nature's Match hog feed. I don't know if I should attribute the problem to this though, as the young trio was raised on it and is showing no issues, none of the babies ranging from pinks to hoppers show any changes, and my rats and ASF's are showing no changes. I was hoping to get other's opinions on what this could be, if i need to switch foods, and if all the mice need culled or just those showing issues. Or, if the mice without tumors bellies may heal. Thank you for any input.
Draven

If I was in your position I'd get rid of any mice with tumors and any mice related to the ones with tumors..aka..the parents of them*if you still have em*, and their babies or just dump all of them and start fresh. Especially since you don't have THAT large of a colony.. I just had to cull half a dozen weaner rats today cause they were all half-wits and could only run in circles...mildly amusing when you put em all out on the floor and they all just run in 6" diameter circles over and over. LOL, it looked like a mini rat circus...but still they were defective, and I like to have 100% healthy feeders.

Also as far as the ones with sores on their bellies/teets...this is their last litter...replace them after their young are weaned(or sooner if you think you can foster their young)..

Feed them of and start your colony from scratch again.

Breeding mice is not very hard the hardest part is to get started, once you get started with a healthy stock it will be a smooth ride.

I would cull them ALL and try to find a good breeder in the area to get stock from.

Are you sure they're tumors and not abscesses?
It's possible that they're just puss pockets from bite wounds, the last two mice clearly have some injuries.