Ive never had an underweight horse before so when my arabian started to lose weight I freaked. My papaw had phenomia so he went to the hospital and couldnt take care of him so he lost some weight due to not being wormed and my other horse stealing his food when he was fed. What weight gain supplements work? Which are senior friendly? He is 14 + yrs old and he is hard to keep weight on. Would veg. Oil work in his food? Don't now a lot about weight gain as I've never needed to know.