The Fibre Requirements of Horses and the Consequences and Causes of Failure to Meet Them

SIMPLE SUMMARY: After water, fibre is the most important component of a horse’s diet. Its value in providing energy is too often underestimated. The energy availability and protein content of pastures and preserved forages depend on the pasture species and the maturity of the pasture at either grazing or cutting. Foraging is a core natural behaviour of horses and ponies and, when possible, takes up most of their daily time budget. Insufficient foraging opportunities result in behaviours that either mimic foraging behaviour or represent an oral occupation. Many of these behaviours are related more to the foraging activity than to the fibre intake. Even those animals on concentrated rations that are rich in fibre are associated with behavioural activities related to a lack of foraging opportunity. Even though foraging directly affects fibre intake, most studies have focused on the behavioural activity of foraging and associated chewing. Replacing starch in a high-energy diet with a fibrous alternative greatly reduces the risk of gastrointestinal disease and improves digestion, body condition, behaviour, immune function, athletic performance, and adaptation to weaning. In many cases, failing to feed the horse its fibre requirement reflects a lack of knowledge on the part of the owner. ABSTRACT: Failure to meet the minimum forage requirement of 1.5% of the horse’s bodyweight and the opportunity for foraging for a minimum of 8 h a day (not going without this opportunity longer than four to five consecutive hours) can have both physiological and behavioural consequences. To provide an energy source for horses, rations often include starch rather than fibre. This can result in health issues related to the gastrointestinal tract (GIT) in the horse. In the stomach, the main concern is equine gastric ulcer syndrome (EGUS) and, more specifically, equine squamous gastric disease (ESGD). Ulcerations are caused either by increasing acidity in the stomach (from starch ingestion and reduced saliva production) or splashing of acidic juices caused by a lack of a forage barrier prior to exercise or prolonged periods without fibrous feed intake, which allows the stomach to collapse and spread acidic gastric fluids into the upper squamous regions of the stomach. In the hindgut, starch that has escaped digestion in the small intestine causes microbial instability and increased production of volatile fatty acids (VFA) and lactic acid. This puts horses at great risk for acidosis and subsequent laminitis. Shifts in the hindgut microbiota will also affect a horse’s behaviour via the gut-brain axis, as well as potentially compromise immune function. Reduced fluid intake caused by reduced saliva production can result in colic. Choosing a fibrous alternative for starch in a high-energy diet greatly reduces the risk of EGUS and acidosis and improves digestion, GIT pH, body condition, behaviour, immune functions, and performance. Providing hay can reduce crib-biting, wood-chewing, coprophagia, the consumption of bedding, aggression, and stress, and subsequently increase social bonding and affiliation with conspecifics. Adequate fibre intake is related to reduced clinical signs of EGUS, reduced reactivity, and better adaptation to weaning. Lignophagia (wood chewing) has also been observed in horses that are foraging, and this is thought to reflect low fibre content in the available forage (for example, early vegetative, lush pasture).