A huge amount of time, effort, and money often are invested in the preparation of horses for various athletic events, including Thoroughbred and Standardbred racing, three-day eventing, steeplechasing, dressage, hunter-jumper events, reining, cutting, and endurance racing, to mention but a few. Regardless of discipline, we expect that a well-trained and properly schooled horse will be competitive. It is therefore not surprising that failure of a horse to perform up to expectations can result in a very high degree of frustration and cause us to ask why. Very often, this situation presents a particularly difficult diagnostic challenge for the veterinarian.

In this article, we’ll look at some of the reasons for so-called poor exercise performance. Our focus this month is to understand why some of these conditions can limit exercise ability. Next month, we will delve further into this topic by considering the approach your veterinarian will take in trying to sort out the reason for apparent loss in (or lack of) performance ability.

What Is Poor Performance?

Simply stated, poor performance is the inability to exercise or perform at a level previously observed or at a level that can be reasonably expected based on the horse’s physical characteristics and state of training. The veterinarian usually is presented with two main scenarios when dealing with exercise performance problems. The first is a horse which clearly has suffered a loss of proven performance. The second scenario in-volves an unproven horse which is not performing up to the expectations of the owner and/or trainer–in many cases, these expectations are overly lofty and in reality there is nothing medically amiss with the horse.

Let’s use a racing Standardbred or Thoroughbred horse as an example. In the first scenario, the horse has been racing well, and has perhaps even won a race or two. During this same campaign, however, the horse mi