Bees do not like horse or mule sweat. If the animals can get away by running they will do so, but confined horses/mules can be killed.
I had a shetland pony for my kids, left the bee yard gate open one day when working the bees. Left for lunch, the little mare went into the bee yard, got around behind the hives away from the gate and knocked over a hive. Before I found her she was stung so badly that she died. Spent the rest of that day cutting wood for her funeral pyre. Then I had to tell the kids.
Mine got into the bee yard the other day. Made a mess of things, but it was too cold for the bees to sting them. I worry about them doing that when the bees are flying and getting trapped in the bee yard.
My father-in-law has kept bees for thirty-something years on his farm, not far from the cattle and horses ....... a good fence separates the bee "house" from the pasture, but I've seen the animals graze very close to the hives and never seen a problem ...........