I’ve done mine, back when I had more horses, but have now used the veterinarian for many years. Partly for reasons mentioned above (possible reactions, possibly needed treatment being covered), but also because this gives me a relationship with my veterinarian.
The vast majority of years, my horses have historically never needed anything in addition to standard care (vaccinations, Coggins, dental). But, because I have a longstanding, ongoing relationship with my vet, stretching from the mid-80s, he has given me his private number and encourages me to call him for advice, even though I’ve not been a high dollar client in the past. And, last week, he voluntarily did me a favor and came out the next day for a blood draw – total charge $40.
That’s priceless to me.