What I do is mix rep-cal with D3 with minerall without D3. This is done before supplementing, not in a batch.
It gives me flexibility in dosing D3, so animals with higher needs (babies, females with eggs) get slightly more repcal, and others get just a small fraction.
Repcal is very high in D3 - much higher than it "needs" to be. So I cut it.
I like having the repcal available in full strength, in case I need extra D3 (resuce, sick baby, etc.)
I like having minerall, as when they're outside, I don't give them much D3 at all. And, minerall has many more minerals than repcal does, so they get a good balance.