I feed Manna Pro - it doesn't contain corn, and it's one of the few limited options I have here.
Many suggest either Oxbow Bunny Basics, or Oxbow Benne Terre - I trust neither. Oxbow's Benne Terre contains cranberries, and much like cats, rabbits aren't capable of metabolizing the Benzoic Acid in cranberries.
Look at the table. Where it says, "Hippuric Acid = 100%" and "Benzoyl Glucuronide = 0%" that means any Benzoic Acid they ingest, gets excreted entirely as Hippuric Acid. Research Hippuric Acid Toxicity. It's a nasty thing. If you don't believe that, read a couple pages prior to the table where it says cats lack the metabolic pathway Benzoyl Glucuronide, in order to metabolize Benzoic Acid. Then look at the table again. Cats excrete 100% Hippuric Acid when given Benzoic Acid, and they excrete 0% Benzoyl Glucuronide. Scroll up to look at the row of information for rabbits, rabbits excrete 100% Hippuric Acid, and 0% Benzoyl Glucuronide... resulting in Hippuric Acid Toxity.
Oxbow's Bunny Basics contains Menadione Bisulfite Complex, which is a successor of Menadione, a synthetic Vitamin K that's so sensitive, it will change when the light, or temperature changes in the slightest.
"Knowing that a pet food company would opt for a synthetic ingredient in contrast to a natural ingredient is bad enough, but it takes one step further on the ‘bad scale’ with Menadione Sodium Bisulfate. This ingredient can be highly toxic in high doses. Hazard information regarding menadione lists “carcinogenic effects” and states “the substance is toxic to kidneys, lungs, liver, mucous membranes. Repeated or prolonged exposure to the substance can produce target organs damage.” http://www.sciencelab.com/xMSDS-Menadione
More information on menadione sodium bisulfate and pets can be read at http://www.dogfoodproject.com/index.php?page=menadione."
"Vitamin K can be supplied to the animal from a combination of sources: vitamins K1, K2 and K3. Vitamin K1, also known as phylloquionone, is found in green leafy vegetables and vegetable oils. Vitamin K2 is produced by gut bacteria and vitamin K3 is chemically synthesized. Vitamins K1 and K2 are "active" upon absorption. However, vitamin K3 must be "alkylated" by gut bacteria or tissue enzymes to become active. This activation involves the addition of isoprenoid side chains, and in some literature this activated form is called menaquinone or designated as MK-4."
A little bit on the actual chemical itself:
No.... there are no reports of actual toxicity resulting from Menadione Bisulfite Complex...but it's one of those ingredients I feel much safer, and much more comfortable staying away from.