Actually, I think there is a a very good reason senior foods are lower in protein. My eight year old has developed hepatic nodular hyperplasia, which is a lesion on his liver and is extremely common in middle aged to old dogs. It was discovered when an ultrasound was done after his liver enzymes were measured and found to be extremely high. The high protein and fat in dog foods increases liver enzymes, and as dogs get older they are more prone to get these lesions. In one study, lesions occurred in ALL dogs over 14 years old.
http://www.petmd.com/dog/conditions/endocrine/c_dg_hepatic_nodular_hyperplasia
