Pig is just as intelligent as a dog 中的pig何不加冠词

问题描述

It has been said that pig is just as intelligent as a dog.

这一句的 pig 是集合名词吗? 为何不跟 a dog一样也加冠词 a?

Thanks in advance.

老师答疑

黎老师：

应该说：It has been said that a pig is just as intelligent as a dog.