most places like jeffers sale the newborn size with a feeding tube syringe combo. http://www.jefferspet.com/weak-kid-syringe/camid/LIV/cp/S7-W6/ I have a few on hand just in case they are needed. They also have stomach tubes but you could always get some tubing from mcmaster carr in other sizes. I have been lucky and never needed one for adults (knock on wood) so the others will need to chime in with sizes for the older ones. Always warm the tubes in warm water to make them more flexible though (not really needed for the weak kid one though because the other ones are firmer). We had a small foal size one and then the larger horse size but I can't remember what size the foal one was sorry.