Hi,
Bringing weight off an obese rabbit should be done very slowly to protect the liver. Rabbits metabolize fat differently than other animals and a quick weight loss causes the fat to be processed thru the liver resulting in damage. The way to a healthy weight loss is to reduce calories a little at a time. We had a mini-lop come in at over 10 pounds....she should have been about 6.5 pounds. Her humans at the time had thought they had a sick French Lop and fed her high calories. It took us over a year to bring her weight down but she is now slim and trim at her correct weight.
Start by reducing pellets by about 10% while offering unlimited grasshay and a handful of greens every night. Continue to reduce pellets by a small amount each week. Keep in mind that by feeding high quality hay with greens and fresh water, rabbits will live a much healthier life as nature intended. For the most part, pellets are much more for our benefit and convenience that any benefit to the rabbit. Most pellets are in the 14-16% protein range and in reality, a rabbit's GI tract is made to work on much less protein. We have a pair of Flemish that top the scale at over 25 pounds each....and they get less pellets per day than most people feed their tiny dwarf bunnies. Idon't care if any of my rabbits eat pellets as long as they eat their greens and hay. We use pellets only to maintain weight in sick or older rabbits. Ever seen an overweight wild rabbit? Probably not since they eat as nature intended. And contrary to popular belief, the inner workings of cottontails and domestic rabbits are identical. In fact, I use the same protocols on domestics and rehabbing wild rabbits...they are the same as far as husbandry goes. Just for info, the difference in domestics and wild rabbits are two chromosomes. By the way...even on such a small amount of pellets....our Flemish are still gaining weight and our male should top out well over thirty pounds...he is still a growing boy. The girl will be a little smaller as she came from an abuse situation in which she nearly starved before coming here.
Plenty of exercise is important too. Not only will that burn calories, movement plays an important part of keeping the GI tract operating as designed.
Slow and steady are the proper way to drop weight from this rabbit. It seems you are talking about a 25% reduction...that is huge but in the long run, it will be in the bun's best interest.
Randy