Meeting the dietary and behavioral needs of the free-ranging, trickle feeding, herbivore horse has become increasingly important due to domestication and modern management practices, such as stabling for long periods of time and restricted access to forage (Harris et al, 2017; Lesimple et al, 2019).
Consistent climate changes over the past 50 million years have meant that the horses' digestive system has evolved to function on a high-fibre, low-starch diet, which they rely on to maintain good digestive health. Modern feeding practices, particularly for the performance horse (Bulmer et al, 2015), can involve high levels of starch compared to fibre, resulting in a multitude of physical and mental health problems such as equine metabolic syndrome, laminitis, equine gastric ulcer syndrome (EGUS) and the development of abnormal behaviours, to name a few.
In the wild, horses typically spend 16 hours a day foraging and rarely fast for more than 2–4 hours (Harris, 2005). It has been evidenced, however, that stabled horses typically spend 8.5–12 hours a day on foraging-related behaviours (Ellis, 2010), not nearing the amount of time typically spent performing this behaviour in the wild. Modern management practices such as stabling (Harris et al, 2017), restricted turnout options (Leme et al, 2014) and restricted forage (Ellis, 2010), all impact the horse's innate behavioural need to spend most of their time foraging, leading to mental health problems such as oral stereotypies (Nicol, 1999).
Physical: equine metabolic syndrome
Starch and sugar are classed as non-structural carbohydrates (NSCs) and are a main source of energy in a horse's diet. Low amounts of NSCs can be found in natural food sources such as grass and hay, but high amounts of NSCs can be found in commercially produced feeds sold by modern feeding companies. Performance horses are typically fed a higher starch diet than most other horses, due to the energy content required to be able to perform (Bulmer et al, 2015). A high-starch diet, however, can be a contributing factor towards the development of metabolic disorders such as equine meta-bolic syndrome (Hoffman et al, 2003), particularly in horses that are not using the energy to perform, but instead storing this as excess adipose tissue. Obesity is the main risk factor associated with equine metabolic syndrome (Morgan et al, 2015), and equine metabolic syndrome can be a predisposition for laminitis, a debilitating, painful condition resulting in damage to the epidermal and dermal laminae within the hoof (Mitchell et al, 2015). Not only can laminitis ultimately lead to the euthanasia of the horse, but management of the condition can also include box-rest and a limited forage intake, again restricting the innate free-roaming and foraging behaviours of the horse, and ultimately affecting the mental wellbeing of the horse.
Mental: oral stereotypies
A high-starch, low-fibre diet and a restriction on time spent foraging can lead to the development of oral stereotypies (McGreevy et al, 1995). Oral stereotypies include weaving, crib-biting and wind-sucking (Nicol, 1999) and can be defined as behaviours that are repetitive without an obvious function or goal (Mason, 1991; Clegg et al, 2008), caused by physical discomfort, hunger, or most importantly in this case, a frustrated motivation to forage (Nicol, 1999). It has been shown that horses who have restricted forage intake are at a higher risk of developing oral stereotypies (McGreevy et al, 1995). Oral stereotypies are often an indicator of poor welfare or sub-optimal management practices, such as housing conditions or feeding practices (Surrafchi and Blockhuis, 2013), as a result of not being able to perform their natural behaviours (Ruet et al, 2020). Oral stereotypies may lead to an increase in salivary flow, reducing the acidity of gastric tract (Nicol, 1999), often leading to secondary health issues for the horse such as equine gastric ulcer syndrome. Even if nutritional demands of the domesticated horse are met within the diet, the lack of opportunity to perform chewing behaviours, dependent on the way forage is presented to the horse, can result in an increase in the likelihood of the development of oral stereotypies, and redirected behaviours such as wood chewing (McGreevy, 2012).
Conclusions
In conclusion, a high-fibre-based diet, accompanied by trickle feeding management practices, whereby the horse has the freedom to perform foraging behaviours, is crucial for the health and wellbeing of the horse. Modern management practices and external factors can often be highly influential in whether caretakers can meet the horse's nutritional need for forage and provide opportunity for the horse to express this behaviour. Caretakers should make it their priority to seek to enrich their horse's environment so that such behaviours can be expressed and nutritional needs can be met, in order to safeguard their horse's welfare.