I didnt read the entire post but are they SMZ's? If so, they dissolve in water very easily. I put JUST enough water on them to make a paste- doesnt take much. Then I put just a tiny bit of molasses in it and put it all in a syringe. Be careful if you go out to my herd with a syringe in your hand cause they think it's candy and will run over you to get it!! They forgive you pretty quickly, LOL!! This way you are getting the correct dose down them and know for sure they are getting it all.
If it is a pill that does not break down quickly in water, then you can crush it and do the same thing....
I had a mare get bit on the nose about 2 1/2 years ago and am lucky to still have her here- I caught it JUST seconds after it happened. If I had not, it would have been too late and she swelled bad enough the nostril on her good side even swelled shut. Was able to get some tubing up the one side so she could breathe. She foaled one week to the day later and was almost back to normal at that point.
Hope your little one is ok and recovers without any problems! My neighbors had a couple bit by a slightly different type of rattler and they lost a couple of dogs and a horse that summer.
I also highly recommend the yogurt too- make sure it says on the carton that it has LIVE bacteria (culture) in it. So many nowadays do NOT. Also a Bayer aspirin will help with pain and fever. It has to be REAL aspirin, not tylenol, ibuprofin or other stuff.
I'm not a vet, just passing on what my vet has passed on to me.