Sometimes it can be a long tedious, and MESSY proposition. We syringe a little, holding the horse's head so he doesn't drop it and let everything fall out. Then we massage the throat. And we keep repeating that until the syringe is empty. I try to get as many as 6 big syringe- fulls in them.
Believe it or not........we had a full sized mare come in with a "funny tummy" yesterday. It was gas because she had pooped. So, we gave her a half dose of banamine and I syringed a combination of vinegar and water into her mouth. It was interesting seeing me try to hold her head up. Yes, she wasted a lot of it, but I got some down her because I just kept giving her more. I massaged her belly and sides for awhile.........About 3 hours later, she pooped again and was hollering to go back with her friends.
Sure hope your little one with the colic is better!