by Tamara Scully

Horses 20 years of age and older are generally classified as senior horses in the United States. Other countries begin that classification at 15 years of age. Horses over 20 years old account for almost 12 percent of the equine population in the U.S., and properly caring for these horses is a prime concern.

Dr. Amanda Adams, of the University of Kentucky, oversees a herd of senior horses, and is focused on determining the nutritional support needed to keep older horses healthy as long as possible. Using the University’s horse population, she’s identified and classified six distinct types of senior horse, based upon their physical status and feels confident that these categories are pertinent in the general population as well.

“I’ve dedicated a significant percentage of my career to study the effects of old age,” Dr. Adams said. “There are a lot of senior horses out there. Know the type of senior horse that you are feeding.”

Classifications of the senior horse include: the healthy horse with no metabolic abnormalities; the metabolically healthy horse that is hard to maintain; the horse with pituitary pars intermedia dysfunction (PPID), also known as Equine Cushings disease; the horse with PPID and insulin dysregulation (ID); the obese horse without ID; and the horse with Equine Metabolic Syndrome (EMS). Each classification requires different nutritional guidelines, Dr. Adams explained.

PPID is a common disease of senior horses, and is not breed-specific, occurring in all breeds. With PPID, the communication between the adrenal and pituitary glands is compromised, resulting in abnormally high levels of many hormones. Signs of PPID include excessive hair growth, with a long, wavy coat developing, as well as exercise intolerance, lethargy, decreased performance and chronic laminitis. The disease has early and late stages, so prompt diagnosis is important in maintaining health.

EMS tends to occur primarily in certain breeds, and is characterized by insulin resistance and laminitis. Obesity is not a pre-requisite for either disease, and EMS can occur in conjunction with PPID.

Assessing aging

While aging is typically measured in chronological years, looking at biological aging provides a better idea of physical health. As chronological age increases, functional mobility, disease and disability increases. Biological age provides a snapshot of health during the aging process, and a chronologically older horse can have a lower biological age than a chronologically younger one, Dr. Adams explained.

As aging occurs, immunological functioning decreases. The immune system becomes less responsive, and inflammation increases. The immunological response to vaccinations is weakened. Endocrine functions change. Musculoskeletal changes occur, and osteoarthritis develops. Teeth and gum issues become a concern, parasite loads can increase, and colic can occur. Nutritional changes are needed to offset and help control some of these concerns.

“How can we help these senior horses to age successfully? How can we support the immune system? How do we support, nutritionally, the different types of senior horses that are out there? It’s an area that needs attention, and there’s a lot we don’t know,” Adams said.

No matter which type of senior horse you may have, proper veterinary care, with a minimum of an annual check-up, is important. To determine whether the horse has metabolic issues, bloodwork to evaluate the endocrine status is needed. There are insulin tests that can be done in the field, such as the oral sugar test, where a bolus of sugar is fed, and the insulin response after 60 minutes is recorded, to measure insulin resistance. A body conditioning score (BCS), a dental exam, lameness examination and routine vaccinations are a part of the health assessment. A fecal egg count is important, as horses seem carry a higher parasite load as they age. Finally, an examination of the environmental stressors — housing, herd mates and social status, as well as any other conditions that could add stress — is also needed.

Nutritional support

Once the health status and biological age of the horse is determined, a nutritional plan to optimize health is needed. For each classification of senior horse, an appropriate diet can support health, prevent age-related decline, and increase longevity.

Metabolically normal, healthy senior horse: “Be proactive,” Dr. Adams said. An all forage diet, feeding between 1.5 and 2.5 percent of body weight, is the goal. High-quality forage is feed, with added balancing pellets to enhance vitamin and mineral uptake if needed.

Metabolically normal, hard keeper: This horse has a hard time keeping weight on despite normal metabolic functioning, and good quality forage should be consumed at the rate of 2.0 – 2.5 percent of the body weight if no detrition issues are found. Adding concentrates will increase the caloric intake, as will increasing fats and crude protein intake. Dividing consumption into two feedings is recommended. Check for parasites and dental issues. If there are dentition concerns, a commercial complete feed without hay may be needed. Dentally compromised animals cannot consume forage as they should be, and hay pellets which can be soaked are useful. Increase calories by adding fats and oils, or beet pulp.

PPID without insulin dysregulation: The BCS is good here, and the insulin response is normal. The concern is polyuria — the production of large volumes of urine — and hyperhidrosis, or excessive sweating. Maintaining proper electrolytes by having enough fresh water for the horse to access regularly is key. Feeding a good quality protein is also important. “Pay attention to the water consumption in these horses,” she said.

PPD with ID: “This is probably one of the hardest horses to maintain,” Dr. Adams said. “We don’t want to spike the insulin responses in these horses.” Supportive nutrition includes testing the hay to keep non-structural carbohydrate (NSC) levels below 12 percent; restricting pasture access; and adding a different form of calories such as fat and beef pulp.

Obese without ID: Slow weight loss is the goal here. A grazing muzzle, increasing exercise and feeding all-forage diets at a lower percentage of bodyweight are all tactics to help with weight loss. “Once you’re at an adequate body condition score, you can maintain that animal on that diet,” Dr. Adams said.

EMS with ID: “You are really worried about laminitis in this horse,” Dr. Adams said. “You want to manage for weight loss with this horse.” Soaking hay to decrease sugars, feeding low-NSC hay, and restricting pasture turnout are means of controlling decline, and ration balancers may be needed. The diet “needs to be tailored per each individual horse.”

“Biological age is important. The goal is lifespan equals healthspan,” Dr. Admas concluded. “There is really still a lot that we don’t know in terms of how, exactly, these special-needs senior horses respond to these different diets.”