The spots are caused by coccidiosis. I raise new zealand whites commercially, and the surest way to control the disease is through cleanliness. The coccidiosis is caused by microscopic organisms. It can be spread in the fecal matter or water supply. Use of any "sulfa" drug is the surest way to control the disease. These drugs can be purchased locally at a farm/animal supply such as Southern States Coop or any store that carries drugs for other animals. The most common one will be "Sulmet", it is a Sulfa-Methazine drug and should be used in strict accordance to the label, it can be very toxic if over dosed. I use this drug, 1 ounce to the gallon of water, for control and have no serious side effects. You should treat water for 4 days and then untreat for 4 days. Most cases require 2 treatment cycles to be most effective. If you plan on butchering the rabbits for meat, you should treat them no more than 5 days prior to butchering to allow for the drug to pass through their system. There is "NO" cure and the disease will always be present, however, only when it flares up does it cause the white spots on the liver. Coccidiosis poses no threat in the meat, but the livers are rendered useless. (At least I have never heard of anyone eating one with the spots) I hope this helps a little, if ya have any questions or comments, please feel free to contact me.