noun
adult dog; fully-grown dog
Refers to a dog that has reached physical maturity, typically after one year of age. Often used in contrast with 子犬 (puppy).
このドッグフードは成犬用です。
This dog food is for adult dogs.
子犬のときと比べて、成犬になると落ち着いてきた。
Compared to when he was a puppy, he has become calmer as an adult dog.