Why is my mom's horse losing weight so quickly?

My mom's horse is a 15 hand tall quarter horse. He's about ten years old and has always been well-built. The previous owner moved to another state and left him and another of our horses back here and my mom fed them every day for about two years before they became ours. That whole time she was feeding them they usually went without hay. Last year they gave both horses to us and they got hay and grain every day, including the grass in the pasture in the spring, summer, and fall. In the past month he's dropped at least fifty pounds, maybe one hundred. He's gone from muscular and built to ribby and sunk in. What could be wrong with him? He gets wormed every month.

This is something that needs to be seen by a vet. For a horse to lose that much weight that quickly means that there could be a very serious health issue at work that should not be played with. I hope you get it figured out and get him back to being healthy.

Another vote for a call into the vet.

If a horse has a sudden change in condition like that there has to be a reason.

It could be something as simple as a need for some serious dental work. Call the vet and find out.

Another vote for calling out the vet!

Let's made it a quorum, shall we? Call the vet!

Well we called the vet and she said to worm him for five days straight, then two weeks later to give him another dose, so hopefully that works.

Have his teeth been checked?

Also along with that much wormer - please give a probiotic to balance the flora in the gut.

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.

I am surprised a vet would do that without seeing the horse. I vote for getting a second opinion.

I don't understand why the vet would think it was worms if you are on a good worming routine? You said you were worming once a month...how could it possibly be worms? I would call a different vet...and I agree with the getting the teeth checked. Is the horse actually eating...do you see it chewing and swallowing? Is it with other horses? Is it a stallion or a gelding?