Hey Jacksapp,
I just read your post about your girls' frequent mammary tumors. Are your girls related at all? Honestly I would be concerned about putting them under again for removals....anesthesia is very hard on the system and the more often it is done and harder it becomes for them to revive. Frequent anesthesia can also cause irreversible damage to the heart over time. I would also question if you needed to put them under so soon after the first removal....is your vet certain that the other lumps and bumps were actually mammary tumors rather than abscesses or sebaceous cysts (which are harmless)? More info here:
http://ratguide.com/health/integumentary_skin/cysts.php
And here:
http://ratguide.com/health/integumentary_skin/abscess.php
Sebaceous cysts can pop up everywhere sometimes. They're completely harmless and usually can be expelled with a little squeeze like a big old zit.
In regards to mammary tumors, there is a medication that works on estrogen receptive tumors-- it is call tamoxifen.
Book mark this ratguide webpage because it is super handy as a reference for just about everything you will be dealing with while owning ratties. Here is the article on mammary tumors. It also mentions the tamoxifen towards the bottom of the page:
http://ratguide.com/health/neoplasia/mammary_tumor.php
What type of rat block do you feed? I would find one high in soy meal. You can also supplement your current rat block and add in the soy by including roasted soybeans/soy nuts but make sure that there is no salt added and they are unsalted. You could also add in shelled edamame for extra soy in the diet.
Quoted from a reference on soy and mammary tumors in female rats:
"Several studies have shown that feeding female
rats miso, a soybean product, as 10% of their diet, had a protective effect against induced
mammary tumors. When combined with tamoxifen, the
soy diet was almost 100% effective in
preventing the
tumors."
Harlan Teklad makes a couple of rat blocks with a high soy content .The 8640 and 2018 have soy in their ingredients. The 8640 has soy as the first ingredient but it has a higher fat and protein content so you'll have to be watchful for weight gain:
https://weecompanions.org/healthy-food
Unfortunately Harlan Teklad has begun to remove soy meal from most of their rat block diets since its inclusion can interfere with studies in a clinical environment. Luckily for us though, they still have the 8640 and 2018 available with soy.
I hope this helps!