Lactation is also very much hot. I like to think of the mechanics of a cow girl finding out that if she milks her chest too much, she'll feel those udders start to grow to keep up with the expected milk production, but if she tries to hold it in until she starts leaking they'll grow anyways to try and accommodate the built-up milk reservoirs in there, and in doing so create more milk-generating mammary mass that just keeps exacerbating the problem after she's emptied herself