Horse in harness found in Pompeii. [bbc.com]
No, not even daddified. The horse probably died from the poisonous gases released during the eruption. It then would be buried in the volcanic ash falling on to it. The moisture from its body would combine with these ashes to form a sort of natural plaster cast around the body of the horse. The temperature would not have been enough to sterilise the body which would rot away leaving the outer cast and some bones and perhaps any metal parts of its harness to remain inside this volcanic cast.
Was the horse mummified?
Looks like they were making a cast of it in one picture, so I guess it was like the people, with the hollow space where their bodies had been but only bones inside. You've seen the casts of the human victims & one dog, I would imagine. Very heartbreaking.