Table 1 contains conversions from inches measured around the heart girth to estimated weight. A condition score system (Figure 1) has been developed at Texas A&M based upon visual appraisal and palpable fat cover. Horses are rated from emaciated to extremely fat. Horses should be fed based upon a percentage of their body weight (Table 2). Once the horse’s weight has been estimated you can calculate the amount of feed it will require. Don’t measure feed by volume; weigh it on a scale (Table 3).
It is difficult to separate condition and fitness from nutrition in performance horses. The horse that has been laid off for the winter may come into the season underweight or overweight. So, part of the program may include weight gain or reduction.
A good fitness conditioning program combined with proper nutrition influences energy use. The performance horse uses 80–90% of its feed for energy metabolism. The muscles can actually be trained to use energy substrates (carbohydrates and fats) more efficiently. There are two general muscle fiber groups: fast twitch and slow twitch muscle fibers. Glycogen (carbohydrate) is the stored form of energy that hard-working fast twitch muscle fibers use most. Research has shown that glycogen can be increased by 33% during a conditioning program of10 weeks. Slow twitch fibers are associated with endurance-type activities. Endurance conditioning can increase the aerobic capacity, or ability to deliver and utilize oxygen and energy-rich fatty acids. Both groups of muscle fibers respond to endurance training by increasing the aerobic capacity. This is one key to a good conditioning program.
There are many ways to condition horses. The best conditioning programs increase aerobic capacity and prepare them for the actual work they will perform (Table 4). One conditioning system is known as interval training. Interval training builds horses up gradually to the actual work that will be expected of them. Interval training stresses the horse’s cardiovascular and locomotor systems during repeated short exercise bouts interrupted by rest or recovery periods. This work-rest system builds resistance to the stress of exercise and slowly conditions horses to their maximum potential.