Possibly either try Mazuri 9F, which has a bit more fat in it, or mix in some hog feed/grains, and maybe some high quality senior dog food, such as Dr. Foster & Smith or Wellness(no iams or nutro crap).

The cat food is a bit too high in fat and protein and may ruin their kidneys. Try for the seed mixtures/grain mixture and possibly adding some dog food/hog feed. My mice really thrive on the hog feed, so much so that they don't get lab blocks anymore. They would just waste the blocks and litters would get eaten for lack of protein. I don't feel that 16% protein is enough for mice/ASF rats. Regular rats, yes, with some supplementation of other things(grain mixture).