by Dr. Eleanor Kellon, VDM

"Performance horse" makes us think of things like speed work, endurance, upper level eventing and showing, but it's much more than that.

Let's define performance horses as those being asked to perform work in excess of their regular activity.

Feral horses travel as much as 20 miles per day in search of adequate food, water and salt. If you consider that as a baseline, horses grazing on good pastures or standing around in a stall or paddock all day have a long way to go to match it. Not so for a horse being ridden.

Keeping things at the walk for a moment, the feral horse is doing a lot less work than one carrying a rider. If you doubt that, try going about your daily activities wearing a back pack containing 1/5 of your weight. Carrying weight roughly triples the energy burned. An occasional stroll through the fields is one thing but if your horse is regularly doing trail rides, he's a performance horse. So is a horse or pony taking care of beginner riders several hours a day.

Obviously there is a difference between those horses and a horse in endurance training or any other extremely strenuous effort but they are more alike than you might think in the ways their bodies have to adapt.

As always, calories is the easy part. Increased calorie requirements depend on the individual metabolism (e.g. Thoroughbred versus air fern Morgan), duration and intensity of exercise. Your, or your trainer's,. experience with the individual and work type will determine how much to feed. The bottom line is always to maintain an appropriate body condition score.

However, when the speed of the work increases to trot or canter on a regular basis, this requires an adaptation of the muscle metabolism above and beyond what is needed by a feral horse moving around primarily at the walk. Carrying weight and advanced movements also increase demands on the muscle compared to what the horse's genetics provide at a baseline.

A robust response to the demands of exercise is facilitated by a targeted blend of key amino acids, minerals, vitamins and metbolites plus adaptogens to support a balanced stress response. Some horses struggle in specific areas such as breathing or have muscular challenges like meeting training milestones or muscular bulk.

Read more: Any Horse in Regular Work is a Performance Horse

by Dr. Eleanor Kellon, VDM

It's never bad to be aware of things that may be toxic to your horse, but precautions can be carried too far if you don't know the details. Yes, selenium is a potentially toxic mineral (they all are) but deficiency is much more common.

An owner contacted me because she had a hay selenium assay done which showed she was feeding about 3 mg per day from the hay, but she was horrified to realize the horse had been receiving another 2 mg per day on top of that. The bare minimum requirement for an average size horse is 1 to 2 mg/day.

However, bare minimum requirements are a long way away from toxic and even the 5 mg/day is considerably below any intake that would be dangerous. It is estimated an average size horse would need to take in at least 20 mg/day to be at risk for chronic toxicity - i.e. toxicity that takes weeks to months to show up. Acute toxicity takes over 1500 mg/day.

Naturally occurring chronic toxicity can occur with hays having over 5 ppm selenium ( = 50 mg in 22 lbs of hay) but this is rare. Natural toxicity is more likely in animals grazing on very high selenium soils where wild selenium accumulator plants, which contain several hundred ppm selenium, are growing. The highest selenium soils in the USA occur in pockets of Wyoming and South Dakota. These soils are high saline shales with an alkaline pH.

Acute toxicity causes a neurological derangement called "blind staggers" and is fatal. Chronic toxicity, "alkali disease", causes loss of mane and tail hair plus disrupted hoof growth resulting in separation of the hoof capsule at the coronary band. Another symptom of selenium toxicity is a DMSO or garlic-like odor on the breath. Recovery from chronic toxicosis takes up to 10 months if the hooves slough off. Again, both of these are rare.

Read more: Lose Your Fear of Selenium