Fetching details from the dictionary...

(animal) collar
necklace; choker
子犬の成長に合わせて頚輪のサイズを調整した。
The collar size was adjusted as the puppy grew.
頚輪が緩すぎると散歩中に抜けてしまう。
If the collar is too loose, it will slip off during walks.
光る素材の頚輪を付けて夜間の安全を確保した。
A reflective collar was put on to ensure safety at night.