We went for a nice long walk around the property, did some de-shedding, and then I FOUND POOP!
And confirmed that he thinks dirty puddle water is tasty. Despite having just walked him for 20+ minutes, he wanted to follow me around the pasture anyway.
And we put on a spiffy new fly mask, because yesterday it was raining, last night it was freezing, and now it’s 60+ and the flies are out. 
So, to sum things up: he’s eating, he’s drinking, and he’s pooping. 
The watching his weight continue to drop while I have to slowly increase his food intake is going to kill me, but we’ll get (back) there eventually. He seems pretty damn happy today.