I'm curious about where this idea comes from - the alfalfa-based feeds say "for all life stages" (as do a lot of the timothy-based ones). Since the timothy-based feeds cost at least 4 times as much as the alfalfa-based ones (though the nutrient breakdown is similar), does feeding this ultra-expensive feed really have that much of an advantage over feeding alfalfa-based pellets and hay?
I should have clarified that I was referring to indoor, fixed rabbits.
Some of the problems not uncommon in some house rabbits is obesity, bladder sludge, and GI issues. High calcium and protein levels are usually blamed which is why high protein and high calcium legume (alfalfa)- based pellets are discouraged.
This is also the reason some vets are recommending not only that adult, indoor, fixed rabbits receive timothy-based pellets because of their lower percentages of protein (12-14%, as opposed to the 16%+ found in many pellet feeds), but that the amount of pellets fed be severely restricted as well.
With the recommended pellet amount for an average adult (5-7 lb) rabbit being just 1/4 cup per day, the higher cost of timothy-based pellets is negligible. A 10 lb bag can last 4 months for 1 rabbit. So those of us with a couple indoor house rabbits aren't spending very much on pellets.
This has been the common understanding in the world of house rabbits-- to lower that protein percentage and calcium level once a rabbit reaches around 6 months of age (adult) by switching from legume (alfalfa) based products to grass based products.
However, I will also say that I have been reading some somewhat contrary literature that blames some of these health issues not so much on whether the pellets are alfalfa or grass based, but on the fact that almost all pellets have an abundance of soy and grains.
Soybean hulls, oat hulls, and wheat middlings, are found in many pellets -- whether alfalfa-based or timothy-based. It has been suggested that these extra by-products in pellets are more to blame -- that if a rabbit is not fed soy and these types of grains but is fed higher percentages of both timothy (grass) and alfalfa
hays, that their digestion will be healthier.
This study focuses more on the bad added extras in traditional rabbit pellets (whether timothy or alfalfa based). This company sells rabbit pellets that are soy/grain free and are comprised of hays, supplements, and (I believe) flaxseed.
http://sherwoodpethealth.com/the-science/#alfalfa
My take on this is that for those with house rabbits, that if one is going to be getting pellets from a traditional source (pet store, etc), then adult rabbits should be getting limited pellets that are timothy-based. However, if one is willing to purchase online, then perhaps Sherwood Pellets are the way to go. With grains and soy by-products out of the picture, then their mix of timothy and alfalfa pellets seem good.
Rabbit owners will have to make their own choice based on their take on the various studies.