给定一个段落和一个单词，请使用上下文中的线索填写空白处的单词。


段落：There are many different types of animals in the world, ranging from small insects to large mammals. Some animals, like dogs and cats, are kept as pets by humans. Other animals, like cows and chickens, are raised for food. Still other animals, like birds and horses, are used for entertainment or transportation. A veterinarian is a type of doctor who specializes in treating __________.
单词：（根据上下文补全）
animals