Most commercial rabbit food is alfalfa-based. Just look at the ingredient list — it's almost always first. But, as we learned recently, it really is no good for rabbits. It doesn't just make them fat, as we thought. (Being fat is bad for rabbits, aside from the usual health problems with being overweight, because they can no longer bend far enough to clean their nether regions.)
Alfalfa also increases the calcium content in their urine, making them susceptible to bladder and kidney stones. It can also cause white gunk to build up near their genitals. This causes the urine to soak into the fur, causing urine burn. We've had one rabbit, named Kahlo, recovering for about 4 weeks now. She's almost healed but the regular baths and ointment were hard on her and us. We would hold her hind end under a faucet to rinse out the urine from her fur and put Desitin on the sore skin areas. Our vet told us you don't merely want lotion or aloe vera because those don't repeal liquid. Diaper rash ointments such as Desitin repel urine, helping the skin to heal.
Our vet said alfalfa-based feed is OK for young rabbits, until about a year and a half, because they're growing so fast but that it should be discontinued for adult rabbits.
So you might be asking why the rabbit food companies make alfalfa-based food. So I asked the vet. She said she had no idea but that perhaps it's because alfalfa tastes good so rabbits gobble it down and if a rabbit gobbles down every bit of your competitor's food and not yours, you're going to do what's selling better for the competitor rather than what's better for the rabbits. My own theory is that it's cheaper. Alfalfa is a fair bit cheaper than other grasses. For us to buy a bale of alfalfa rather than a bale of grass hay, it's about 25 to 30 percent cheaper. So if your food is 25% more expensive than your competitor's, you'll lose sales because most people are shopping by price since their rabbit is "just a pet."
We get lots of free rabbit food donated to us but it's all alfalfa based so we'll switch to the non-alfalfa stuff even though it means more out of pocket expenses. The problem is that timothy-based rabbit feed is $63 for a 50-pound bag. That's just crazy. A neighbor told us that, for rabbits, you can feed them grass pellets that are meant for horses, which cost only $11 for a 50-pound bag. Real grass hay is supposed to be the main diet of rabbits, and all of our rabbits get it. But these rabbits were raised on pellets so they prefer them. We give them both grass hay, pellets and lots of fresh veggies. We haven't tried the grass pellets yet but we will — ooh, or maybe we'll mix them with the timothy pellets...