I have used "Blue Seal, Pig & Sow" grain with no adverse effects. It's only about $10 for 50#. The only drawback that I encountered was the small pellets do not sit on my feeding trays (it falls through) and it gets wasted. A larger block pellet (Mazuri Rodent Block) will sit properly in my tray and the rats eat only what they need and the rest stays in the tray until the rat is hungry again. Much less waste.

Rick