Rabbit food may sometimes contain mycotoxins or contaminants, particularly lower quality feeds or if it was exposed to moisture and became moldy. This can make a rabbit very sick and could be fatal.I just lost my rabbit to what they thought was cancer, and now my second rabbit also has high WBC count and will be starting antibiotics tomorrow. Neither one has been exposed to other rabbits but did recently add another grain to their diet for the first time in years. I was wondering if a bad batch of grain or hay could be toxic or have something that could make them suddenly sick. I doubt hay and grain is tested as much as dog or cat food. How do they monitor rabbit food if there is a toxic mold or substance?
I believe it would be your state's department of agriculture that tests animal feed. I think you have to pay for the testing unless there is clear evidence of many rabbits becoming sick from a feed, then the manufacturer likely is responsible.
You could always ask your vet.
I'm very sorry for the loss of your rabbit.