diamond is one brand made by a large company called schell & kampeter, which makes many different products.
the best they have to offer being "chicken soup" and premium edge. the diamond line is mostly byproduct based, so not something i'd recommend. other lines they make include professional pet foods, nutra nuggets, nutra gold and country value. they also do contract manufacturing for third parties, such as for example the kirkland signature brand sold by costco.
i hope this will be of some help. more on the topic
here.