@Moonkissed: not everyone gives main vegan food because of the owner's moral.
On Dutch forums, a lot of experienced people suggest (scientifically proof is not fully given, but they see a difference) that a vegan main diet prevents tumors and kidney problems.
That is the reason why I feed mainly vegetarian.
Rats do need animal proteins for growth (most stop growing when they are 8 months), so I feed them by this schedule:
The first 12 weeks, you give the rats animal proteins daily.
Then until 6 months: 2-3 times per week.
Until 1 year: 1 time per week. If you see they are still really growing after the six months, you could give a little bit more.
After that: only once in a while, but less than once a week.
*Every portion is about a tablespoon big.
N.B.: If a rat has had tumors or kidney diseases, you feed them no animal protein at all.
And I give them good animal proteins, so with the least amount of processing: fish, eggs, cooked chicken, living/frozen insects and high premium cat foods (here almo nature and applaws, which I would actually eat myself no problem if I was starving, because the chicken looks like actual chicken!).
Sometimes I will also give a little bit more processed foods like dried insects.
You could also use a high quality dry dog food, but only the high (so expensive) quality ones. Since I only have 2 (in a week 4) rats, I will not buy the doog food, since you can't really get it in small bags.
So yes, you can feed your rats a mainly vegetarian diet, but only from a specific age.
I myself use Science Selective, but I am not sure you can purchase it in your country.