We’ve been aware for some time of the balance between the delivery of nutrients for athletic performance in horses, and their psychological and physical health. Traditionally, performance horses were fed large amounts of grain to deliver adequate energy, with little or no regard for the forage part of the diet.
Plenty of research now exists to show that starchy, grain-rich diets – especially when coupled with low forage intakes – are unhealthy and cause both psychological and physical compromise. Gastric ulcers, developmental orthopaedic disease (in youngsters), colic, reactive behaviour and rhabdomyolysis (tying up) are just a few of the disorders linked to grain-rich, low forage diets. Some genetically gifted horses seem to be able to run fast despite health issues such as gastric ulcers, but thankfully their welfare is being paid more attention these days.
In the past two decades many lower starch, higher digestible fibre and oil-supplemented compound feeds have become available for hard-working horses, with good results. Such feeds deliver more of their energy from digestible fibre sources and vegetable oil, with less from starchy grain.
Feed manufacturers tend to include a certain amount of starch in such feeds with the aim of helping muscle glycogen replenishment in hard-working horses. Muscle glycogen is the key fuel for performance, and suboptimal levels result in earlier onset of fatigue in some events. It’s not just starch and sugar that are used for muscle glycogen replenishment – one of the volatile fatty acids produced from fibre digestion – propionic acid – can also be used.
Researchers from Brazil and the US, have recently shown that diets low in non-structural carbohydrates (NSC; includes starch, sugar, fructan) may not allow adequate muscle glycogen repletion, which is likely to have an inhibitory effect on performance. Researchers in Sweden have shown that optimal growth rates and performance are possible in young trotting horses fed forage-only diets (albeit forage of high energy content). Such forage seemed to supply enough NSC – along with propionic acid – to ensure adequate muscle glycogen levels.
But what is the optimal amount of dietary starch for a hard-working horse? Currently, we don’t know. Perhaps the best answer at the current time is to source very good quality forage with a relatively high energy and NSC content so that compound feed intakes don’t have to be excessively high. What might be as important as the actual level of NSC intake is periodization of training to ensure muscle glycogen is replenished adequately, since horses replenish their muscle fuel more slowly than humans.
Whilst we are yet to find out the perfect way to feed the hard-working performance horse with high energy requirements, it seems sensible to find a balance that maintains good health whilst maximising physiological capabilities.