Definition & Meaning of "[sweat] like a (pig|horse)"

What is the origin of the idiom "sweat like a pig" and when to use it?

The term "sweat like a pig" likely originated from the misconception that pigs are sweaty animals due to their large bodies. In reality, pigs do have sweat glands, but they regulate their body temperature primarily through other means such as urinating. It is used to describe someone who is perspiring heavily or excessively, often due to physical exertion, intense heat, nervousness, or anxiety.