What are you feeding them that it only contains 3 ingredients? That seems highly sketchy and insufficient. If you are feeding them a complete and balanced commercial feed, it would have a lot more than 3 ingredients to ensure that all of their nutritional needs are met. And if you are not feeding them a complete commercial feed, you need to really know what you're doing in order to get the right balance, and even then, you may not get it right. Mixing your own feed is very hard to do right and usually not worth the effort and expense.I think my boyfriend's concern is that the dry feed only has 3 main ingredients which seems limited when you think about what most birds eat naturally.
Here's the ingredients list for one of the more popular feeds, Purina Flock Raiser (the one I use). A lot more than 3. The chickens don't need anything else besides this (other than calcium).