Physiology of Equine Aging

Seniors don’t necessarily have to be race-ready or prepared for competition, but keeping an older horse exercising has many physiological benefits.

Photo: Anne M. Eberhardt/The Horse

We’ve all known and loved that special senior horse—the seasoned teacher, the care-taker, or the ruler of the barn. And while aged equines are common today—approximately 11.4% of the U.S. horse population is more than 20 years old—this wasn’t always the case. Advances in research, veterinary care, and nutrition have all aided in giving horses a chance at longer, healthier lives.

For example, we knew little about aging horses’ physiology until the early 1990s. That’s when Karyn Malinowski, PhD, professor and director of the Rutgers University Equine Science Center in New Brunswick, New Jersey, and colleagues began their research on the topic. Since then, they’ve made crucial discoveries.

Malinowski shared some of the most important findings from over the years at the 2017 Annual Mid-Atlantic Nutrition Conference, held April 6 in Hunt Valley, Maryland.

Exercise is Important

Scientists generally agree that horses typically begin to show physiological signs of aging by 20 years. With age, their aerobic capacity declines and they can develop arthritis, insulin resistance, and changes in body composition and immune function. But exercise and training can actually attenuate many of these age-related declines, improve body condition, and decrease insulin resistance.

“Exercise and exercise conditioning for older horses is a good thing,” Malinowski said.

In one study Malinowski worked on, older horses showed a significant decline in percent body fat and an increase in muscle mass after 12 weeks of exercise training.

“The horses looked great,” she said. “They actually waited at the gates to come to the Equi-Ciser (a horse walker) for their workouts.”

Thermoregulation

Senior horses also experience a decrease in their ability to regulate body temperature (called thermoregulation), because the heart works harder to get blood to the skin and tissues. Exercise can certainly help keep the heart strong, but older horses will likely still have some difficulty with thermoregulation in extreme temperatures.

Hormonal Changes

Age also affects the endocrine (hormonal) system. Specifically, Malinowski said, “cortisol is necessary to mobilize glycogen [energy] stores. In older horses, there is a blunted response of cortisol concentrations to exercise, which may put the older horse at a disadvantage.”

This decreased cortisol response can be somewhat mitigated by exercise training, but is not completely restored to that which younger horses experience. In sum, it appears to be a little harder for the older horses to utilize and restore energy reserves, making recovery time longer.

Inflammation

Malinowski also touched on the low-grade, chronic state of inflammation, defined as an increase in inflammatory cytokines, senior horses experience called “inflamm-aging.” She said inflammation increases with obesity, and calorie-restricted diets resulted in a decrease in some inflammatory proteins.

In addition, heat shock proteins (HSPs), which play a role in proper cell functioning, including insulin signaling, increase to a lesser degree in older horses compared to young after an acute bout of exercise. This could have additional implications for insulin sensitivity and recovery from exercise.

Take-Home Message

Seniors don’t necessarily have to be race-ready or prepared for competition, but keeping an older horse exercising has many physiological benefits. And while they need some special consideration when it comes to warming-up, exercise intensity, and cooling down, Malinowski said “exercise is necessary for the continued well-being of older horses.”

About the Author

Nettie Liburt, MS, PhD, PAS

Nettie Liburt, MS, PhD, PAS, is an equine nutritionist based on Long Island, New York. She is a graduate of Rutgers University, where she studied equine exercise physiology and nutrition. Liburt is a member of the Equine Science Society and is currently senior equine nutrition manager for Mars Horsecare US/Buckeye Nutrition.

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