Let's just say you feed 3/4 alfalfa cubes and 1/4 oats.
If you fed 300# alfalfa cubes, that would provide 300Mcals. (1# of alfalfa has approximately 1000kcal or 1 Mcal).
100# of oats would provide 130Mcals. (1# of oats has approximately 1.3Mcals).
300# of alfalfa cubes + 100# oats will provide 430 Mcals.
A typical Senior feed has about 1.5 Mcals/#. To get those same 430Mcals, you would need to feed 287# of senior.
From a transportation stance, that's a savings of 123#. Now that's not the whole picture as I would not totally eliminate the cubes from the diet as you want some type of long stem forage for them to chew on and help with digestion but you can see where I'm going.
Can the mill that makes the cubes add oil to the binding agent? Adding 5% oil will increase the caloric value to 1.15Mcal/#. It's not going to increase the volume you transport but now you've managed to add a few more calories. A small mill is not going to want to lose your business and if you're talking 10+T of product it's so worth their while to work with you. What's a batch size for them? That will probably be what they want to make in a run.