I think they must be quite hot indeed, especially on warmer days. But the strange thing is that especially shetlands apparently are known for the fact that they keep their winter coat for a long time. Blacky and Sjors sometimes shed the last long hairs even in may/june and I was quite worried about that, but then I heard that most shetlands do, especially if the nights stay coldish / there are some rainy days, then they seem to play at safe and stay prepared for the next ice age in full summer.
Speedy is shedding his winter coat quite fast now, although he too seems somewhat hot during training occasionally. Last training sessions every time we quit he had sweaty ears!
His brains are overheating! Poor pony, apparently I make him think too much.
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New horse book: Mandala horses! Never stop making mistakes!
Natural Dressage