Yes, joint supplements can work for horses. These supplements often contain key ingredients such as glucosamine, chondroitin sulfate and MSM (methylsulfonylmethane) which help to lubricate the joints and reduce inflammation in the horse's body. In addition, many of these products also include omega-3 fatty acids that can help improve overall joint health. It is important to note however that it may take some time before you start seeing results from using these products. Therefore, it is important to consult your veterinarian when selecting a supplement for your horse and follow their instructions regarding dosing and frequency of use.