Hummmm... Well, Some horses are left to the elements of winter and have survived for centeries...
Last year I received a rescued PMU farm (
Pregnant
Mare U
rine/Premarin)mare. She survived being pregnant, dehydrated, and exposed to the elements of winter in Canada before reaching my home in the states. She was in extremely poor health from the lack of care and simply put... she surrived...
You are receiving answers here from people who take extra steps in caring for their horses. I personally don't understand the point of having horses if they are simply left to roam with zero amount of care.. . But I'd have to agree with the answer you gave to your own question
My horses have never really had any shelter and it gets cold, it even dropped down to like 19 degrees one night. They have a pasture and just roam free, There in there mid twenties and have never missed a step so I guess there doing fine.
Your horses or your parents horses have probably become accustom to their environment and may have some really good grazing land that keep weight on them.
Much the opposite to my horses... They wear blankets when the weather is 35 degrees F or below, they sleep inside a barn at night, and get fed sweet feed, crimped oats and fescue hay each evening, but this is what they have become accustom to so this is what they need and what I must do for them in order for them to stay healthy.
As long as your parents horses not bony and sickly looking, I'm sure their OK and have adapted to their environment being that they have lived this way for 20 something years.
Kae