I am reading 'Black Beauty' by Anna Sewell. (1877)

What would be the meaning of 'came in warm' in the below paragraph?

> "Jerry kept us very clean, and gave us as much change of food as he
could, and always plenty of it; and not only that, but he always gave us
plenty of clean fresh water, which he allowed to stand by us both night
and day, except of course when **we came in warm**. Some people say that a
horse ought not to drink all he likes; but I know if we are allowed to
drink when we want it we drink only a little at a time, and it does us
a great deal more good than swallowing down half a bucketful at a time,
because we have been left without till we are thirsty and miserable."


Is it an expression no longer in use?

I've never come across this kind phrase in modern English.