1lb of most ration balancers is probably roughly equivalent in calories to 2-3c of most grain products, though you'd have to weigh the specifics of each. But it might also be less, as 3c of some grains could easily be 1lb and have 1500-1700 calories, where the 1lb of the RB is down in the 1300 range. Maybe significant, maybe not.
If 3c is 1lb of your chosen RB, and you choose to feed 2c total, then that's 2/3 of the recommended serving, so if you felt the need to add a v/m on top, you should feed just 1/3 to maybe 1/2 of the recommended serving - not really worth it
All feed should be weighed if it's new to you so you know exactly the right volume to weight ratio Most pelleted feedstuffs are in the 3c/lb range, but I've had several folks tell me Enrich 32 weighs out to 2c/lb, so you definitely need to make sure you know, especially when you're feeding smaller amounts
______________________________ The CoTH CYA - please consult w/your veterinarian under any and all circumstances. - ET
I feed EquiShine pellets and oats. If I feel the horse needs more protein I look around for supplements or add alfalfa/roasted soybeans if the horse can use the extra calories. Usually, my horses don't need the extra. Everyone is pretty toned and shiny - even the idle one.
Horses not in hard work do not need a huge amount of protein in their diets as long as they have the right kind of protein. Before you get all bent out of shape looking at the protein content of the grain, get your hay tested. Horses get more protein from their hay than their grain, and more calories too. Once you have the base to work with, you can fill in the holes if there are any. Your local extension agent can help you with this. Feedxl looks awesome.