Your horse may not be specifically wanting to lie down more often – he may just appear to be because of the difficulty he has getting up. In the summer, horses might lie down more often because they enjoy sunbathing when they feel secure, but in the winter this is unlikely. A horse tends to lie down when he wants to take the strain off an ache – such as sore hocks or arthritic pain – and may have difficult getting back onto his feet for exactly the same reason.

If you are sure that your horse also has swollen joints, it is possible that your horse has osteoarthritis (Degenerative Joint Disease). The symptoms of osteoarthritis are very similar to what you describe – specifically stiffness getting up and swollen joints, and it would not be uncommon in a horse of his age. This condition is as a result of the cartilage that protects the joints degenerating. If left untreated, this condition is likely to eventually result in lameness, as the cartilage would eventually be destroyed completely, resulting in bones grinding together in the joints.

If your horse is not required to do much work, often a period of rest and application of ice packs is enough to relieve swelling, but in more severe cases anti-inflammatory medication is required and in rare cases surgery. The other possible causes of swollen joints are mostly autoimmune in nature, and your vet may wish to take samples of the joint fluid for testing. A thorough veterinary examination of the horse will be able to determine the cause of the swollen joints.