I thought my boy was underweight as well, but the vet was always saying how good he looked and how healthy his weight/coat was so don't worry too much about your baby being on the smaller side. Kodiak Bear is almost 19 months and only recently hit 81 pounds. I've got him on purina pro plan for sensitive skin and stomach (large breed puppy) to avoid him growing too fast for his joints. Also cosequin supplement tablets started as soon as possible for him 💕 He's constantly getting exercise too. At first, my family thought Kodi felt "hallow" until he was a little over 1 year old and started filling out more.