Is it bad to keep my dog on puppy food too long?

It's not going to poison them, but it's not doing them any favours either. Puppy food is deliberately calorie-dense and higher in fat, protein, and minerals like calcium, because a growing pup burns through energy and needs the building blocks to lay down bone and muscle. Once your dog's finished growing, all that extra richness has nowhere useful to go. The usual result is weight gain, and a bit of pudge creeps on faster than most owners expect.

Timing depends on size. Small breeds tend to reach adulthood around 9 to 12 months, medium dogs around a year, and big breeds like a Lab or a Huntaway can take 18 months or even two years to finish growing. Large and giant breeds are the ones to watch most closely, because too much calcium while they're still developing can affect how their joints form. Feeding them up to help can quietly do the opposite.

The switch itself is easy. Once your dog's near their adult size and their vet's happy they've matured, move them onto a good adult food over about a week, mixing in a little more each day so their stomach keeps up. If you're not sure whether your dog's ready, your vet can tell you in a two-minute chat at the next visit. Happy Hour's lamb kibble is made for adult dogs, so it's an easy one to move onto once your pup's done growing.