Puppies, even puppies from the same litter, grow at different rates. This is particularly true when you start looking at different breeds. Small breed puppies reach their full size long before large breed puppies do.
New puppy owners have a lot to think about: is my puppy eating the right food? Is my puppy growing at the right speed? Is my puppy getting enough food? Too much? Why is my puppy eating weird and gross stuff he or she finds outside?
Another thing new owners worry about is if their puppy is too thin, or veering towards overweight. Is your puppy looking a little on the thin side?
Puppies tend to lose their chubby puppy-ness at around eight to 10 weeks old and start to lean out. This is a natural phase of growth. Puppies may veer from skinny to slightly overweight at various points in their growth cycle.
Puppies shouldn’t grow too fast: puppy food is formulated to encourage them to grow at an optimal rate, which doesn’t mean as fast as possible. Puppies that grow too quickly are at risk of health and skeletal issues.
There is a useful tool called the body condition score that vets use to assess how puppies, and full-grown dogs, are doing with their weight. If your puppy has a score of about four or five (you can feel the ribs, but not see them, and your puppy has an abdomen tuck from their rib cage to their back legs) you have nothing to worry about!
But if your puppy has visible ribs, lumbar, vertebrae, and pelvic bones, he or she probably needs to put on weight. Puppies should reach about one half of its weight by around four months old — this varies from breed to breed, so talk to your breeder or another expert to see what a reasonable metric for your specific puppy is. Some breeds, like the Greyhound, tend towards being lean and ribs being slightly visible may not be a concern.
The most likely cause of a puppy not gaining enough weight is diet.