I have been feeding my rabbit a popular name brand rabbit food. I was recommended that I change my food to another brand that meets the needs of my rabbit better. Do I need to do anything special when changing their primary diet like this or is all rabbit food basically the same?
In my experience the digestive health issues are one of the primary causes of rabbit mortality in pet rabbits. Anything diet related should be considered carefully before changing. There are many rabbit food options, a rabbit's dietary requirements change through it's life cycle, or your bunny may be on a food that is was chosen for it's marketing instead of it's appropriateness. In any case, changes are potentially fatal; leading to bloat or GI Stasis.
In our (my wife and I) volunteer capacity we almost constantly have bunnies staying with us in our home. For visiting bunnies, they arrive with the type of food they are already eating. We keep them on that diet the whole time. If a bunny will be changing diets while staying with us, they stay 100% original the first week, then 75/25 the second week, 50/50 the third week and 25/75 the fourth week. On the fifth week, they are 100% new diet (assuming no issues).
During the entire change process we closely monitor their intake and dropping for signs. We expect that the intake will remain consistent through out the change, as they are getting a measured amount of pellets (1/4 to 1/2 a cup per 5 pounds of body weight), decreases are the only likely change.
If your bunny was on a low fiber diet, the probably had small poops, and you would expect to see an increase in size of them.
If your bunny was on high calorie diet, they are probably making more cecotropes than they consume, you would expect to stop seeing these and you would expect the color of the normal droppings get lighter in color.
If the bunny is new to you it is important to wait a week before starting the change so you become familiar with dietary, elimination and other habits so you will recognize if there is a change. As prey animals they naturally cover any signs of illness, symptoms that are more evident in dog, cat or child or much more subtle in a rabbit.
During the pellet food change do not make any drastic changes in treats or fresh greens. It is always ok to NOT give high sugar foods like apples and carrots. If the rabbit is used to inappropriate amounts of high sugar foods you can withdraw those immediately but wait an extra week before starting the pellet change to allow the digestive system to re-balance.
Your bunny should have timothy hay 24/7 and a daily severing of fresh dark green vegetables. Do not add new vegetables during a pellet change, if there is a change in the rabbits health you will not know if it is from the new pellets or the new vegetable. New vegetables can be added to the diet after your bunny is stabilized on healthy pellet. As with the pellet change add some to of the new kind with old, for the first few days. But you can go straight to a 50/50 mix.
As a staple green we use Romain or Green leaf lettuce (NEVER ICEBERG), if a bunny does not have greens in it's existing diet, either of these is a good place to start. In my experience Romain tends to have a longer shelf life in the refrigerator, so it is my primary choice.
Treats are an important part of training and relationship building with your bunny. When shopping for treats (and food) if it is bright color, then don't buy it. Brightly colored foods tend to be aimed at getting the attention of the shopper, with little or no attempt to meet the health needs of your pet. Personally we use "Vitakraft Nibble Rings" you can add these to your bunnies diet from day one, but try to limit to one a day (particularly during a diet change). They can be broken in to 2 - 4 pieces and provided multiple treats events while staying at a one per day ration.
I would say to have some sort of a gradual transition, you should start off by giving him his normal amount of food. Instead of giving him all of the brand you intend on switching him to, you should mostly fill the bowl with his old food, with a few pellets of the new food. Do this for a couple of days. After a few days, gradually increase the percentage of new pellets until you are completely on the new food.
Note: This is only a guide. You should monitor how the rabbit is reacting to the new food. You may need to go slower.