It does sound a bit excessive, I have 18 at that same age and they aren't eatting any where near that amount. Are they out in some serious cold? Could be they are eating extra to help convert it into heat, but I think Nova is probably right, there is some waste going on. I'd suggest getting a bigger feeder, I have a long metal one on legs (nice and tall, like 6-8 inches) and I only fill it halfway. I have to fill it twice a day but I have noticed that they aren't spilling any more and bonus, they aren't kicking bedding and poo into it like they did with the old feeder.