Sprint is resting comfortably. (Perhaps a bit too comfortably, on my couch surrounded by blankets.) The vet said he's pulled through and he'll be fine.
Apparently the cure consisted of Lisa's small fortune, Melanie's babysitting skills (she took Sequoia to her house for the duration), my neighbors' fully-exploited soft hearts (they handled afternoon feedings and cleanup), and my own awesome nursing skills.
I can administer IVs now! And I'm an expert at dog pills, syringe feedings, sponge baths, and diarrhea management. I could totally be a WWII Red Cross nurse. But only if they put me in charge of the horses.
Next step is fattening the calf; he's still a walking skeleton. Then he gets ousted to a new home. In the meantime, I buy another dozen rolls of paper towels and bleach wipes. At least now his diarrhea is brown instead of red. And on that note...