Care of our Geriatric Horses

MVMA Proceedings 2022 Care of our Geriatric Horses

Alison LaCarrubba, DVM, ABVP (Equine Practice)

What do we need to know to best care for our geriatric horses? There are so many facets to horse care and add in age related changes and sometimes things can seem overwhelming. Just like humans, all horses will age differently. Some of this has to do with individual variation, but also there can be breed variation. For example, small and miniature horses are generally known to live a bit longer than are large, heavy breed horses. Also, what do we mean by geriatric? What age horse is considered to be “old” or need extra care? This will certainly vary, greatly in some instances. Generally speaking, it’s safe to say, upper teens and early twenties we will start considering horses entering into their golden years. The average life expectancy of a horse is approximately 25 to 30 years. We all know horses which have lived many years longer than this. A horse named Old Billy is known to have been the longest living horse in the world, having lived to the age of 62 years. He was from Lancashire, UK. Perhaps the most important thing we can do for our older companions is to understand the best nutrition practices. For a healthy adult aged horse, the dry matter (hay and grain component) should contain, 12-14% protein, 0.3 – 0.4% phosphorous, 0.6-0.8% calcium. The total intake should be approximately 1.5 – 2% of body weight, or 15-20 pounds per 1,000-pound horse. Many horses can do well on good quality forage, including fresh pasture grass and good quality hay up into their twenty’s, so long as they can maintain adequate body condition. Other horses will start to lose muscle mass and condition and require supplemental grain feeding and/or a complete pelleted feed like equine senior. Equine senior complete feed is a high fat, high forage, easily digestible source of calories for our older horses with dental problems, who are unable to utilize hay effectively. These older horses with a body condition score at less than or equal to 4/9 require a diet with approximately 12-14% protein, 4-7% fat and this should be fed at 0.5 – 1.0% of body weight. It is important to minimize sugars and starches in horses prone to laminitis or diagnosed with insulin resistance. Forage based pellets or cubes or chopped hay can also be used as a supplement. Omega 3 FA play an important role in inflammation. There are benefits to supplementing omega 3FA in horses with lower airway disease and insect hypersensitivity as well as joint disease. Fats represent a small amount of overall calorie intake in a normal horse diet at pasture. Fats are necessary as structural components of cells, precursors to hormones, carriers for fat soluble vitamins (A,D,E,K) and to enhance overall body condition in thin horses. Fresh grass, alfalfa and clover are natural, quality sources of omega-3 FA’s, even if at relatively low levels. Cut hay is not a good source of omega-3 FA and once grass is cut and dried most of the activity of the omega-3 FA is diminished. Horses being fed grain and hay diets exclusively would benefit from an omega-3 FA supplement. One of the reasons geriatric horses have changing nutritional requirements is secondary to dental attrition or dental disease. Horses are designed to live about 30 years, and so are their teeth. Some horses are outliving their teeth and some horses do not have proper dental care over their lifetime and develop dental disease and tooth loss. Geriatric horses may require more frequent dental examinations, where we look for loose or damaged teeth and we can help manage nutritional needs better when we know how effective their chewing/grinding surface is. In horses with significant dental

attrition, the end goal is comfort, so they can chew without pain. There are some common dental abnormalities that can progress over time in the absence of correct dental therapy, resulting in unbalanced dentition, such as wave mouth and excessive hooks. When teeth develop gingivitis and periodontal disease resulting in attachment loss, the tooth becomes loose and painful and will require extraction. Other reasons we extract teeth include tooth root abscesses and fractured or fragmented teeth. Equine Odontoclastic Tooth Resorption and Hypercementosis (EOTRH) is a painful disease of geriatric horses affecting primarily the incisor and canine teeth. Most horses with this disease are in their late teens and twenties. Clinical signs of EOTRH include inability to bite a carrot with the incisor teeth, pain associated with application of the speculum, abnormal eating, fistula in the gingiva around the incisor and canine teeth, infected teeth, periodontal disease, gingival recession, feed packing between teeth, abnormal angulation, and loose or fractured teeth. EOTRH is diagnosed based on history, clinical signs and radiographs – highlighting the resorptive properties of the disease, along with hypercementosis. Currently the only treatment for this disease is exodontia of all affected teeth. Typically we end up removing all maxillary and mandibular incisors and often the canine teeth as well. The metabolism and endocrine status of each individual horse will be slightly different and this needs to be taken into consideration when feeding older horses. The two most common endocrine diseases effecting horses are Equine Metabolic Syndrome and Pituitary Pars Intermedia Dysfunction (PPID). EMS is not a disease specific to older horses but it can affect older horses and can be what is called a co-morbidity, where horses are affected by multiple different issues which contributes to overall poor health. EMS can in fact complicate other diseases of geriatric horses. The hallmarks of EMS include obesity, which can be global or regional adiposity, documented insulin resistance (IR) and laminitis (clinical or subclinical). The predisposition to EMS can be both genetic and environmental. Certain breeds, known to be “easy keepers” seem to struggle more with EMS – ponies, donkeys, Morgan horses, Paso Fino, Arabians, ASB, AQH and TWH are included. Ponies and donkeys have a tendency toward IR. Not all fat is created equal and fat from different areas of the horse, crest of the neck, sheath/inguinal region, tail head, has been shown to be more metabolically active. There is not perfect test to diagnose IR, but we can combine a variety of testing methods. We typically will start with evaluating insulin and glucose levels in the fasted horse, or a horse which was only fed grass hay overnight. The gold standard for proving IR is the CGIT (combined glucose insulin test IV), but this is not practical in the field setting. We do sometimes opt for the oral sugar test, where we feed Karo Syrup to a horse and check insulin glucose at prescribed times after and watch for time to return to normal. This test is less invasive and more physiologic in that it uses the GI tract for absorption, and it can be done on the farm. Any horse diagnosed with EMS will need to be put on a strict weight loss diet, reducing overall calorie intake, removing them from pasture and even soaking hay to reduce sugar content. Thyroid supplementation can be added in the short term to kick the metabolism into gear and allow for more expedited weight loss. If IR is uncontrolled even after dietary changes metformin can be added in an effort to improve insulin sensitivity. The other common endocrine disease, which is a disease of geriatric horses, is PPID. This typically affects horses over 15 years of age, is slowly progressive and is a result of a lack of dopamine inhibition on the intermediate lobe of the pituitary, secondary to oxidative damage – which results in excessive production and function of certain, specific hormones, such as ACTH. Overproduction of certain hormones (POM-C peptides and cleaved products such as ACTH) can cause the clinical signs associated with PPID as well as resulting in IR. Hypertrichosis is something we think of when discussing

PPID. The pathogenesis of hypertrichosis is unknown, but perhaps related to excess androgens from the adrenal gland, or dysregulation of the thermoregulatory center of the hypothalamus secondary to pituitary compression. Approximately 55-80% of PPID affected horses will display hypertrichosis and grow a long, thick, curly coat, fail to shed and sometimes are affected by patchy alopecia. This tends to be a sign of later stage disease. The ultimate goal is to diagnose horses prior to the development of some of the problematic clinical signs. Other clinical signs of PPID include weight loss, PU/PD, pendulous abdomen, muscle loss/weakness/sway back, lethargy, infertility and dermatitis. Some of these clinical signs are a direct effect of IR which is associated with this disease. Endocrine diseases of horses can be difficult to diagnosis accurately and PPID is no exception. Typically, we make a diagnosis based on history, physical examination findings, a baseline ACTH level, which is a screening test. ACTH is a stress hormone so levels can be elevated during times of stress and pain, and all horses have a seasonal elevation during the fall months (July 15 – Nov 15) further complicating the issue. If we suspect disease and our screening tests are normal, we can then move to a TRH stimulation test (thyrotropin releasing hormone) and this has a better ability to detect disease but is discouraged during the fall season as well, as results may vary greatly. Once diagnosed, we manage the disease through the use of a dopamine agonist, Pergolide. This is not a cure but rather a way to control clinical signs. Finally, musculoskeletal disease in aged horses can be a long-standing cause of pain which can affect overall quality of life. Diagnosing the exact cause of the pain in order to initiate targeted therapy is important for the long-term comfort of our older horses. Many old horses have varying degrees and locations of osteoarthritis. Arthritis can affect any joint and different breeds and disciplines will have varying predispositions. Laminitis can also be a source of pain, associated with other co-morbidities, such as EMS, PPID, or could be associated with a previous illness or injury. Laminitis can truly affect quality of life and be difficult for owners to manage. Soft tissue injuries include stresses and strains to muscle, tendon and/or ligaments. These can be intense or mild, life threatening or chronic low grade. When we discuss soft tissue injures causing long term lameness issues we think about injury to the suspensory apparatus, ligaments associated with joints, muscle strain and tendon injury or disease. Some breeds are predisposed to a condition called Degenerative Suspensory Ligament Disease (DSLD) which results in chronic breakdown of the suspensory apparatus, loss of support of the fetlock, fetlock drop and associated pain. Neurological dysfunction can be secondary to musculoskeletal pain, when we think about conditions like cervical vertebral instability and cervical arthritis. This can result in pain as well as neurological dysfunction and ataxia. Once we understand the cause of the pain, hard tissue, soft tissue, neurological, we can better understand how to treat the horse in order to keep them active and comfortable for as long as possible. There are a variety of diseases and conditions affecting older horses, and this was certainly not a comprehensive list but these are some of the most common conditions we see in horses over 20 years of age. There are many things we can do to help slow the aging process in our older friends and allow them to live not only longer lives, but better quality lives!

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