Oxbow is a lab block. Not in the most technical way, but in rat community vernacular.
It is the best dedicated rat block, but I still do not like it for the artificial additives. I prefer and recommend a dog food called Solid Gold Holistique Blendz. Generally, dog food is not suitable for rats, but this particular dog food is not in any way suitable for dogs. The reasons that make it a terrible dog food actually make it an excellent rat food. The protein is a tad high, but is easily remedied by mixing it with a mix of quality ingredients, which should ideally have a part in a rat diet anyway as variety is extremely important and most helpful in a holistic sense.