Trees as lollipops

My mares (esp the preggo ones) are busy licking the tree trunks. This is an every day activity during what usually is their afternoon siesta time. Is the sap coming back up the trunks and making it "taste" different? All mares do it, but Hennie & Orania spend the most time acting like beavers. Anyone else notice this?

Do you have grass yet? Mine don't and they get bored and start chewing the fences. They've learned it from each other as Diva and Prada don't do it, but Soleil does and she's taught everyone else <sigh> I'm actually quite amazed you have trees with bark on at all!

Yes we have grass - not a lot yet but definitely coming up. They get hay 2x daily and don't seem as interested in the trees when hay first comes out but once they're full that's when the licking starts. One day I took hay out & everyone but Hennie came up & immeditely went after the hay. I took it all the way out to where she was standing @ an old tree w/a large knot in the middle of the trunk. She preferred licking that knot (like a bear with honey - which is why I was wondering about sap) to eating her hay!

Are they maples? Maybe they're getting a maple syrup hit

Sadly too warm for maples (or I'd be out there w/Hennie & Orania). Oaks.