My dog is almost 2 years old and has we've always fed him once a day around the same time. We give him Purina Dog Chow and measure to the specifications on the bag per his age/size. In the past month or so, he has been suddenly eating less. He doesn't finish his food very often, but he'll eat at least half. Any thoughts?

Sometimes when its hot my dog has less of an appetite because his activity level is lower. Has his activity level slowed this last month. As long as he is eating and showing no sings of sickness I would not worry too much. Some breeds don't overeat. If you think there are other signs of something go see your vet.

First, the levels on the bag are recommendations, not gospel. So... is your dog showing any other symptoms? Urinating/eliminating the same? Still playful? More active/less active? Gaining or losing weight? If the only thing wrong is that he's not eating everything you give him, I wouldn't worry about it. If my cats don't eat everything, they get a little less the next day... if they scour the bowl clean, they get a little more.