Large dogs and small dogs have a lot in common. However, there are differences. Consider the following if you’re thinking about bringing home a new dog who has a weight difference of more than 25 pounds from your current dog.

Larger dogs can hurt smaller dogs unintentionally.
Large dogs can run over small dogs while chasing a ball or rushing to greet their owner. They can also cause joint injury during play while jumping on a smaller dog’s back.

If mixed-size dogs have a “typical” dog spat, the damage to a small dog can be significant.
Dogs who live together may have occasional disagreements. For example, a dog may guard a food bowl, a treat or a favorite toy from another dog. If the other dog misreads the signals or tries to take what is guarded and a fight ensues, the small dog is at a disadvantage and can sustain injuries. Injury can also happen if a large dog is frustrated by another dog (say, a neighbor’s dog passing), and redirects that frustration onto the small dog.

Prey drive
There are some large dogs who have an instinctual desire to chase and catch small animals such as squirrels, cats and more. When in a state of excitement (such as running while playing chase), other small dogs—even known ones who are playmates—can trigger that hunting chase behavior and occasionally the catch instinct as well, which can cause injury.

Small dog manners
Because small dogs are less likely to be corrected for “rude” behaviors than their larger canine cousins, they can sometimes develop habits of being forward or aggressive to other dogs, which can provoke the larger dog. Small dogs should be socialized and trained with force-free methods to the same standard as large dogs.

To make sure that a multi-dog household with large and small dogs is successful, owners should monitor interactions carefully, encourage calm and polite behaviors, discourage wrestling and mounting play between dogs, and feed and give bones or other durable chew toys only when dogs are separated.