An increased risk of fractures from falls and decreased bone density in general are familiar consequences of aging in people but not as well researched in horses. However, between clinical experience and what can be found in the literature, there is reason for concern.
A 1979 study [Shorafa, Feaster and Ott] looked at bone mineral content, cortex thickness and fracture resistance in the metacarpal (cannon) bone of horses of various ages. They found mineral content and strength peaked between 4 and 7 years old, then progressively declined.
The 2008 study found here https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2267174/?tool=pubmed found age-related change in the microarchitecture of bone with decreases in the number of trabeculae (structural tubules) and greater distance between them in older horses. This constitutes osteopenia, which is reduced bone mass although not as severe as osteoporosis.
Another factor in older horses is higher cortisol levels, which occurs from aging alone but especially in horses with PPID [Cushing’s]. Cortisol disrupts the normal balance between bone formation and bone breakdown, ultimately resulting in bone loss.
We can’t completely prevent the osteopenia of aging but there are possible contributing factors that are within our control. Check yearly for laboratory evidence of PPID with ACTH level in September, or any time PPID is suspected. If PPID develops, be sure to treat adequately so that ACTH remains in the normal range.
Keep your senior moving! In addition to benefits for joint health and mobility, exercise also helps maintain bone density.
While nutrition can’t cure or prevent osteopenia, improper nutrition can definitely make it worse. The key nutrients are:
- High quality protein and key amino acids: Bone is built on a scaffold of protein/collagen, which then becomes calcified. Whey and the amino acids lysine and proline address this.
- Calcium, phosphorus and magnesium: These are the major minerals in bone. Together with balanced trace minerals zinc, copper and manganese they provide for maintenance of bone.
- Vitamins C, A and D: Critical for formation of collagen and regulation of bone formation.
- Boron: Needed for normal bone density
- Strontium: Assists in maintaining a positive balance between bone synthesis and breakdown
- Silicon: Helps promote homeostatic mechanisms supporting strength in bone and connective tissue
Healthful activity levels, PPID surveillance and optimized nutrition can go a long way in preserving bone strength in older horses.
Eleanor Kellon, VMD