Your horse’s system is designed to operate on large volumes of low-energy feed.  Unlike carnivores, whose digestive systems are designed to survive on, and even benefit from, intermittent meals, separated by various periods of fasting; horses, and other grazing mammals, are biologically designed to have a continual supply of food passing through the gastrointestinal tract.  One feature of this design is that, as opposed to carnivores, who produce stomach acid in response to the intake of food, horses by contrast produce an almost constant supply of stomach acid, whether feed is present in the stomach or not.  To buffer this acid, horses on an appropriate, natural diet will spend two thirds of their day chewing on forage, producing approximately 40 litres of saliva, which contains bicarbonate.  Together, bicarbonate in the saliva and the bulk of the roughage buffer the stomach acid, and then help to create an optimal environment further down the GI tract, where populations of healthy gut flora feed off and process the roughage, out-competing harmful microbes, manufacturing b-group vitamins, and producing usable energy from fibrous material.  Later, in the colon, left-over fibre is your horse's ally in maintaining hind-gut health, reducing the risk of colon disease, and assisting with the removal of toxins via the bowel movements.  When this continual supply of feed is broken, acid will quickly begin to corrode the mucosal lining of the stomach, creating lesions on the stomach wall (or gastric ulcers), and if left for long enough, or if bleeding ulcers become out-of-hand, the stomach will perforate.

The idea of all this bulk can be off-putting to people who show, as a ‘grass belly’ is considered unbecoming on a show horse. Beware though, your horse’s need for dietary fibre MUST be met, because gastric ulceration can be a death sentence, and even low-grade fibre inadequacy has detrimental effects, causing a host of undesirable outcomes (wood-chewing, windsucking, weaving, poor digestive health, acidosis, blood toxicity, bowel disease, colic, behavioural issues etc).

For racing and performance horse trainers the challenge may lie in providing adequate energy to fuel athletic endeavours, or in weighting down the large intestine unnecessarily, and so fibre is sacrificed for energy-dense alternatives. Again, caution and diligence are strongly advised; your horse still needs fibre, as much as any other nutritional element, and in time will come apart at the seams if this need is overlooked.

So how does one provide suitable fibre for their equine companion?

Ideally, as pasture or pasture hay. Variety is important, as any mono-culture fodder will eventually create imbalance and ill-health. . Good, horse-friendly pasture contains a good variety of grass species, is not fertilised with super-phosphate fertilisers, contains limited or no high-oxalate grass species, is low or moderate in NSC's, and has a limited legume content.  High-oxalate species include kikuyu, buffel, sateria, guinea grass, signal grass, pangola and green panic.  If your horse has limited or no access to fresh pasture, the main points to remember are that hay loses vitamin content, and any omega-oil content will also decline in value over time, so your horse’s requirement for supplementation of those elements will be slightly higher than the pastured horse (depending on the quality of the pasture of course). On the other hand, some pasture grasses can be quite high in sugar (high NSC/non-structural carbohydrates) - particularly at night, or after rain - which diminishes on storage or soaking, and so horses with metabolic issues (founder/laminitis) may benefit from hay over fresh pasture, at least during the critical healing stages, or permanently if your pasture is unsuitable (ie. always too high in sugar).

If you are feeding hay, the same guidelines should be adhered to when sourcing your hay. Additionally, hay should never be fed dusty; dust from dry soil or the breakdown of leaf can be dampened down with a spray of water, however mould spores are toxic, so mouldy hay should go straight to the compost heap. Lucerne hay in small amounts can provide your horse with additional amino acids, however over-use will provide far too much protein (taxing kidneys), bind up iodine which then interferes with metabolic health, and has been linked to enterolith prevalence (likely due to its high calcium content, plus phosphate if it has been artificially fertilised). Additional insight suggests that lucerne may be especially unsuitable for horses who are prone to tying up, and removal can significantly reduce its occurrence.

Hay can be fed in slow-feed hay nets, which will help to increase chewing time, and reduce boredom in stabled or yarded horses, as they must work for longer to get through their daily hay supply. A slow-feed net will also enable you to feed less (ie for show horses, race horses or good doers), while still keeping your horse somewhat protected from ulceration.

Chaff of any kind is best used in moderation – just enough to mix through daily feed supplements. Short-chopped chaff does not encourage lengthy chewing as long strands of hay do, so it is usually swallowed before enough saliva has been produced to adequately buffer stomach acid.

Good dietary fibre provision naturally supports your horse’s intestinal microflora populations, improves intestinal transit time to reduce stagnant waste accumulation, supports a healthy bowel and reduces the incidence of gastrointestinal ulceration and colic.

If your horse is already experiencing the detrimental effects of a low-fibre diet, GastroZen may help your horse's system to repair, recover and restore balance more quickly, while you adjust your feeding plan.