Kale, mustard greens, and spinach contain high levels of oxalates (the salts of oxalic acid), which can accumulate in the system and cause toxicity over time. Rather than eliminating these veggies from your list (because they are highly nutritious and loved by most rabbits), limit your use of them to 1 or 2 meals per week.
Chewing items: In addition to nutrition, hay and vegetables are also important to your rabbit's dental health. A diet that requires little chewing produces uneven tooth wear, causing enamel to grow on the sides of the teeth. These spikes can cause severe oral pain and excessive salivation (often called "slobbers"). They also cause reluctance to chew, inability to close the mouth, and reduced food intake. The situation deteriorates as the teeth continue to grow, and, if it is not treated, results in severe malnutrition. In addition to hay and vegetables, you will want to provide your rabbit with chew sticks or gnaw "bones" of untreated wood of various sizes and shapes. Cardboard tubes and untreated wicker can also be used.
Treats: Treats, including fresh fruits, should be given sparingly because of their calorie content. Rabbits can digest small quantities of oats and barley, but again, they generally provide more calories than necessary. And, too much carbohydrate has been associated with enteritis in rabbits.
Feeding rabbits through their stages of development
Like human beings, rabbits need to be fed differently at different stages of their growth to ensure healthy development, digestion, and weight. Throughout a rabbit's life, avoid any sudden changes in diet; new foods should always be introduced gradually. Remember to keep fresh clean water available at all times, too. Water bottles versus dishes are recommended.
Baby rabbits: A baby rabbit, or kit, feeds solely on its mother's milk for about the first three weeks. During the first few days, the milk contains high levels of antibodies that help protect the kit from disease. After three weeks, the kit will begin nibbling on alfalfa hay and pellets. By 7 weeks of age, baby rabbits can handle unlimited access to pellets and alfalfa hay in addition to mother's milk. Kits are usually weaned from their mother's milk by 8 weeks of age, depending on the breed.
Juveniles: Between weaning and 7 months of age, the young rabbit can have an unlimited amount of pellets and alfalfa hay. At 3 months of age, start introducing small amounts of vegetables into your rabbit's diet. Introduce one vegetable at a time. If any vegetable seems to cause digestive problems, avoid feeding it in the future.
Young adults: Young adult rabbits from age 7 months to 1 year should be introduced to timothy, grass hays, and/or oat hay, and it should be available all day long. The fiber in the hay is essential for their digestive systems to work properly. At this point, they will require little alfalfa hay, as well as fewer pellets. Alfalfa hay has more calories and calcium than rabbits need at this stage of development, and the high calorie content of pellets can also begin to cause weight problems. Instead of offering unlimited pellets, a good rule of thumb is 1/2 cup of pellets per 6 lbs. of body weight daily. To make up for the nutritional loss, you must increase your rabbit's intake of vegetables and hay. You can feed your rabbit some fruits during this stage, but because of calories, limit them to no more than 1-2 ounces per 6 pounds of body weight daily.
Mature adults: Mature adult rabbits should be fed unlimited timothy, grass hay, and oat hay. Once again, you should reduce the pellet portion of the diet. A standard guideline is 1/4 cup of pellets per 6 lbs. of body weight per day. Several servings of vegetables are required (2 cups per 6 pounds of body weight daily). Make sure to choose dark, leafy greens, and feed at least three different kinds daily. Iceberg or other light-colored varieties are NOT nutritious. Also, make sure you are offering dark yellow and orange vegetables. Treats, including fruits, must be fed sparingly.
Seniors: Senior rabbits over 6 years of age can be fed the same diet as mature adults if they do not have weight loss problems. You may need to increase pellet intake if your pet is not able to maintain his or her weight. Alfalfa can also be given to underweight rabbits, but only if calcium levels are normal. Annual blood workups are highly recommended for senior rabbits to determine the level of calcium and other components of the blood.