have his teeth checked and if the vet is not willing to do anything but worm him, then find another vet. My bet is teeth, have they ever been floated? We just pulled the tooth on my hubbys gelding, he started to lose weight. He had been floated about 5 months ago, but this was sudden and rapid. Sedated him and checked his teeth again, he has a broken molar, it was split, but still seated in his gums, but imagine how that must have felt as the teeth move side to side to chew, OUCH... Pulled it and he has already started gaining the weight back. He never spit out food, never dropped grain, but guess it was very painful when chewing.