Q: How could my 90-pound Labrador-pit bull mix be underweight? My veterinarian says he is. Considering I was hoping for a medium-sized dog when I adopted him as a puppy (his paws weren't big when he was little), I really am not all that interested in him getting even bigger. Is this a problem? She said he was perfectly healthy.

A: If your veterinarian says he's perfectly healthy, then he's in normal range and you don't have to change a thing. That's the good news. The better news is that there are health benefits to keeping your dog just a little underweight. Long-range feeding trials of littermates fed to keep one 10 percent under "ideal" weight and the other 10 percent over have shown the health advantages of keeping your dog the lean machine he is. Lean dogs are less likely to get cancer, less likely to have orthopedic problems and less likely to suffer from arthritis.

We veterinarians use a physical examination to determine what we call a "body-condition score." You can do the same. You should be able to run your hands down your dog's sides without bumping over each rib. If you press in and slide the skin back and forth over the ribs (veterinarians call this "palpating"), you should easily be able to feel the ribs. Your dog should also have a "waist," or "tuck up" behind the rib cage, but not all that much. Ohio State University's College of Veterinary Medicine has an excellent graphic you can use, at vet.osu.edu/vmc/body-condition-scoring-chart.