Turmeric is great for our horse who is arthritic and gets sore after work sometimes! He also has a magnetic rug and bands on his legs
Some herbal products contain naturally anti-inflammatory substances. Their anti-inflammatory action is less powerful but the side effects much less way missing, so this is a good alternative to Bute in the case of your horse which seems to require receiving anti-inflammatory regularly.
In any case, it is important that your horse be seen by a veterinarian to determine the cause of this stiffness and to treat it if possible.
The Zoetis team