(Edit: Requires Item Stacking mods)
The method I am talking about is to load up 50 babies in 5 stacks of 10. You have 5 slots in the pen for adding animals. If they are grown, you can only add 5. As babies, they stack up to 10 in a stack. So, with 5 stacks of 10, you can grow 50 adults. Once you remove them, you can only return 5 adults to the pen.
So, to get the absolute most from your farm, raise 50 at one time. You can’t do a stack at a time either. Has to be all at once. Put in 50 babies and then load your food. Food can be added over time if you don’t have 50 shadespiced dust meals at the start, but the important thing is getting 50 babies in at once.
This is all if you want to get the absolute max running in one pen. If space for lots of pens isn’t an issue, then load a few at a time and move on to the next as they fill up.
I am getting roughly 150 silver and gold a day now, plus about 3000 iron (2 pens combined). Just add rocks for food