The Horse’s Life Span
Dr. Melissa Mazan
What About My Horse's Cardiovascular System?
Horses have generally been lucky in the nature sweepstakes as far as the cardiovascular system is concerned. They naturally have a very low incidence of cardiac disease and don't suffer from high blood pressure. The heart is a muscle, and it has the ability to strengthen with training - but as with all muscles it deteriorates with age. Luckily, horses have been endowed with such spectacular cardiovascular ability and reserves that few horses (other than the elite racehorse, 3-Day Event horse, or polo pony) need the full capabilities of their hearts at any one time. The older horse's heart usually manages to keep pace with the gradually reduced demands that are put upon it. Older horses are more prone than younger horses to developing heart murmurs due to functional problems, such as aortic insufficiency. Does this mean that they are ready for retirement? Not necessarily. With your veterinarian's approval, many horses with heart murmurs can go on to be useful companions for many years.
How Does My Horse's Respiratory System Function with Age?
It is a good question. Extensive studies of the older horse's respiratory system have not yet been performed. Because inflammatory airway disease (which eventually develops into heaves) has had more time to develop in the older horse, there is a good chance that your horse may develop a cough or breathing difficulties as he ages. This has little to do with intrinsic aging, however, and much to do with exposure to hay, straw, barn molds and dusts, and your horse's own allergic response. In other species, such as man, lung function does deteriorate with age. The lungs become less compliant, or elastic, and breathing becomes shallower and less efficient. Again, however, horses have been blessed with such spectacular lung function to start with, that few horses ever need to call upon their full capabilities. Poor "wind" in an older horse is usually due to poor training, and not poor lung function.
What Happens to My Horse's Musculoskeletal System?
Muscles, bones, and joints all lose some of their resilience, strength, and ability to repair with age. However, it is important to remember that, within limits, the musculoskeletal system improves with use. Muscles rely on nerves to tell them what functions to perform - and neural circuits develop and improve with practice. There is a reason why those Spanish Riding School horses and Grand Prix dressage horses are in their teens and early twenties. It has taken much practice for their muscles to learn to perform such complex and coordinated maneuvers. Muscles in horses and humans alike improve their ability with repetition – truly, practice makes perfect. Likewise, bone improves with use. Although it is not outwardly apparent, bone is a very dynamic tissue, and responds to concussion (meaning the force imparted to the bone as your horse exercises) by breaking down and building back up on a microscopic scale. In the process, the bone strengthens, and that strength develops in such a way as to be maximally useful for the task that your horse is asked to perform.
Joints are less able than muscle or bone to repair themselves. The smooth cartilage that lines the joints and is necessary for pain-free athletic motion is easily damaged. Once the process of osteoarthritis, or inflammation of the joints, has begun, a perfect repair is not possible. Unlike muscle and bone, joints do not respond well to concussion and repetitious motion. Damage begins with overwork and trauma at a young age, so prevention of damage to joints is your best approach to prevent aging of the joints.
As your horse ages, his muscles will lose strength, his bones will not be as strong, and he will likely have at least minor osteoarthritis. If your horse has had a good athletic education, however, his efficiency of motion and training will let him continue to exercise happily, often into his thirties.
What About My Horse's Eyes?
As with all the other body systems, the horse's eyesight does deteriorate with age. The most common problem in older horses has to do with a disease called recurrent uveitis, or moon blindness. This is an inflammatory eye disease that is still very poorly understood. The complications of recurrent uveitis include cataracts and scarring that can lead to blindness. Because this is a chronic disease, we tend to see these complications more commonly in the older horse. Even in the older horse with healthy eyes, the lens of the eye becomes less compliant with age, and the horse becomes less able to focus on objects. This seems to be less of a problem for horses than for species such as cats that rely heavily on good eyesight. Older horses with vision loss need special veterinary attention, but are often amazingly adept at relying on cues from their owners, other horses, and surroundings to help them navigate.
What About My Horse's Internal Organs?
Studies in older people suggest that the most important changes occur in the kidneys. The kidneys become less efficient at ridding the body of waste products, and they become less able to concentrate urine, leading to increased loss of body water. What does this mean? It means that we must be more careful using even "safe" drugs in older horses, and we must make sure that they always have adequate supplies of fresh water, so that they don't become dehydrated.
So, What is My Horse's Life Span?
All of us know of the 40-year-old horse or pony, and with genetic luck and very good care, your horse may also live into his forties. Whether or not your horse will live this long depends on genetics, good home and veterinary care, and a dollop of luck. We generally find that horses begin to show signs of aging in their mid-teens. If they were living in the wild, poor dentition alone would probably lead to a natural lifespan of 12 to 18 years – not withstanding predators and other mishaps. What can you expect for your horse? If we assume that your horse does not suffer a catastrophic event, such as colic or fractured bones, it is reasonable to expect that your horse will live into his twenties, and many will reach their thirties. Good dental and other veterinary care, good nutrition, and regular exercise, will help your horse to live as long and healthy a life as possible.