Well sometimes horses, and I assume donkeys too, get poop in their vulva (some mares have a vulva that extends out too far or is slanted outwards towards the bottom, trapping feces that falls in, its a common problem) and being as they cant get it out, they sometimes get an infection, which may incite flies to lay eggs (only if it progresses to tissue necrosis I'm pretty sure)
I'm thankful that my two mares never had that problem!
Ours too. Its only our gelding finding ways to cut his legs on things that aren't sharp. I have a habit of skinning my elbows on countertops accidentally, so I can sympathize with him.
I am so sorry if that was too much info guys...
But anyway, my fort has expanded into the third caverns and I'm digging what I hope will become a waterwheel power generator loop from the only edge of the map where water can enter, then I'm going to establish a tree farm up above in the enormous solid space below the eastern half of the second caverns (I'm guessing the great 80 z-level chasm in the middle represents a transition between cavern biomes from the mountains to the west to the swamps in the east, which are much lower in elevation? The other caverns don't display elevation change this but maybe they ramp down slowly.) Almost everything has been moved down, and I've decided to go with communal bunkhouses shared for the non-noble dwarves because it's easier and one giant room full of 100+ beds with different owners and a couple cabinets and coffers actually counts as a very nice bedroom, plus anyone spending time in their bedroom instead of the tavern will actually talk to other dwarves and thus socialize. If we can get those water wheels going maybe I can run a mist generator for the tavern...