I’ve also had success with weight loss just by increasing the protein and decreasing the carbs of a grain-inclusive food by mixing it with a higher protein grain free food, ie Merrick Wilderness or Turducken (discontinued formulas) cut with Blue Buffalo Wilderness. For me, at any age, the increased protein and decreased carbs helped the dogs with weight loss. There are some high protein grain-inclusive foods as well, such as Merrick Classic and Acana Classic, and foods designed for puppies generally have a higher protein content as well (but not always) like Nutrisource Large Breed Puppy. I would chose the Nutrisource Performance formula over the large breed puppy formula for weight loss and yes for your senior. It is rated for all lifes stages. You would of course be able to feed a lesser amount.
