Alfalfa is pretty high in calcium, in breeding does they can put that into building kits, bucks may end up with bladderstones.
I´d go for about a level 1/4 cup per 2kg (=2.2 pounds) rabbit in 1/3 oats and 2/3 pellet and again that in alfalfa. Top of with as much hay as they will eat (or play with from what i see some posters here wrestling with).
Although for bucks and does that are 6 months (standard size) or older and not breeding or better lactating, i'd rather feed half that of alfalfa or preferred a fine when soaked grasspellet. Since you don't want either of those fat and they need to put energy somewhere if they don't need it. Also note that between mice prevention and not needing that much energy dense feed i wouldn't want them to have more then they'll eat in about 15 minutes once a day. Same for does with litter only twice a day and amounts going up with age kits. Everything else comes from hay and maybe forage. You need to balance energy and nutrition needs with the volume needed to keep insides moving and in place along with feeding the need to chew stuff.