The Horse

NOV 2018

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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Page 26 of 75 | The Horse November 2018 27 of clearness of vision) and color per- ception; ■ Bullet-hole lesions on the fundus, at the back of the eye, have been associated with significant visual disability; ■ Older horses with senile retinal degen- eration show decreased vision in dim lighting conditions; and ■ Dense opacities on the lens can disrupt the passage of light, creating blind spots. Looking Beyond What We See The reason identifying impaired vision can be tricky is because horses might be able to adapt their behavior when faced with ocular dysfunction, especially when vision loss occurs gradually. Owners, together with their veterinarians, can use these three tests to help assess equine vision: 1. The dazzle reflex This reflex involves the horse's involuntary aversion response (e.g., blinking, globe retraction, third eyelid protrusion, and/or head movement) to intense illumination of the eye. 2. The menace response This test is con- ducted by making a small, threatening hand gesture toward the horse's eye. A horse that can see should blink. 3. Obstacle course testing Also referred to as maze testing, this is a pretty reliable method of assessing vision— probably more so than the menace response, which is known to be somewhat subjective. "If a horse that is unilaterally blind has the other eye blindfolded and is presented with a maze of buckets or other solid objects, it will either freeze or stumble into the obstacles," says Dwyer. "When the visual eye is uncovered the horse will be able to navigate the maze." Supporting Horses With Decreased Vision/Blindness So, the question now remains: How safe is a blind 1,000-pound domesticated prey species with a flight instinct? Our sources agree that attitudes have changed in terms of managing aging equids, and that owners of blind or visually impaired horses should avoid jumping to conclusions regarding the functional consequences of ocular disease or damage. Many organizations exist to support owners of blind/visually impaired horses, and several owner-friendly publications are readily available (see box on page 28). In a nutshell, Dwyer suggests owners fo- cus on the following key areas when deal- ing with a horse affected by vision loss: ■ Social interactions Visually impaired horses typically don't do well in herd situations. They are often relegated to the hollows of the pecking order, frequently being excluded from food and water. The majority thrive with a pasture buddy, be it a calm compan- ion horse, goat, or other friend. Some prefer to live in solitude. ■ Environmental organization Once set up appropriately for safety, try not to move anything in a blind horse's enclosures. Check all fencing, windows, footing, hooks for hanging, and feed and water buckets, etc. for sharp edges to avoid injury. "Blind horses tend to use their muzzles to 'read' their environment, much like humans read braille," says Dwyer. "We want to be certain their sensitive muzzles will not be injured when navigating their environment." Additionally, horses with visual dysfunction benefit from "cues" that indicate where certain objects are in a pasture. Such cues include stone footing near gates, rubber mats near feed/water sources, and rubber tires around trees, to name a few. In addition to simply keeping blind or partially blind horses as pasture pets, some owners continue to actively train these animals. Again, horses tend to rely more heavily on other sensory cues, such as hearing, smell, and touch. Along with auditory cues, owners need to reassure their horses frequently with touch, con- sistently approaching the horse from the same side each time (e.g., at the front of the left shoulder). "Religiously following training and handling routines will help visually Visually impaired horses typically don't do well in herds and instead thrive with a calm companion. This 21-year-old blind mare's seeing-eye pony helps guide her around their small eld. LAURA PALAZZOLO Blind horses tend to use their muzzles to 'read' their environ- ment, much like humans read braille." DR. ANN DWYER

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