It may be somewhat alarming to see your horse, turned out in pristine pasture, ignoring the readily available grass and instead, tucking into a pile of dirt, or even worse, eating faecal material in their stable. There are several proposed reasons for this behaviour. In this article, we look at why they may decide to eat mud or faeces. And if there is anything we can do to prevent this.
Pica is the term given to the desire to eat unusual substances with little or no nutritional value, like dirt, sand or tree bark. More specifically, coprophagia and geophagia refer to the ingestion of faeces and soil respectively. Horses are not the only species observed to eat dirt, geophagia has been observed in many others, including humans and dogs as well as ruminants; or, in fact, most animals reared outside. In humans, pica can occur in association with pregnancy and as such, females are overrepresented. No such gender bias has been observed in horses. Geophagia has been observed in both wild and domestic horses.
Why do they do it?
It has long been proven that sheep eat soil to ingest trace minerals such as copper and iron, which helps to prevent nutritional deficiencies. Some evidence suggests that this may also be the case for horses. It has been demonstrated in a study involving a small number of horses, that those who ate soil had lower serum iron and copper levels than those who did not eat soil. They also had slightly lower haemoglobin levels (although still within normal values). These horses were not clinically anaemic and further, larger studies are needed to investigate this more widely. However, interestingly, in addition to this, soil in sites preferred by geophagic horses had higher concentrations of iron and copper than sites that were not actively chosen by such horses. So there is a potential link between mineral deficiencies and geophagia.
Although it seems highly likely that horses seek out soil for its mineral content, we cannot prove definitively that horses exhibit geophagia because they are deficient in copper and iron as we could question whether or not geophagia itself renders them deficient in these minerals. Wild horses have been observed returning to established “lick sites” repeatedly. As these sites have been shown to contain higher levels of iron and copper than others in the same pasture, we can assume that they are not randomly chosen, but how horses can determine the appropriate site remains a mystery. Horses tend not to try out different sites before choosing one; so perhaps there is some olfactory mechanism at play – either smelling or tasting the soil for its mineral content? Certainly an interesting area for research.
There is a strong correlation between boredom and coprophagia or geophagia, certainly in domesticated horses. Often we have to keep horses stabled for long periods of time, due to management factors, or health reasons such as injury. In general, the longer horses spend indoors, without access to forage, even if it is just for several hours because their haynet has run out overnight, the greater the risk of pica; possibly due to a lack of mental stimulation. As pica is observed in wild horses, though, we must assume that boredom is not the only cause of this behaviour.
Lack of dietary fibre
In general, we recommend a daily dietary intake of at least 1.5-2% bodyweight of dry matter or forage. Youngsters on high concentrate diets, stabled for long periods of time are at an increased risk of coprophagia (eating droppings). Fibre is critically important in the diet to maintain digestive health. Diets that are higher in starch rich concentrates are linked to an increased risk of stereotypical behaviours.
Coprophagia in foals is extremely common during the first few months of life. This behaviour rapidly disappears by five months of age. They usually eat the faeces of their own mother, rarely that of others; leading to the theory that a maternal pheromone may drive this behaviour. It may serve to populate the foal’s digestive tract with “good” bacteria that will help with digestion of forage as the diet adapts. Care should be taken to ensure that the mare has been treated with appropriate wormers, though. This is because coprophagia can lead to parasitic infestation in the foal.
What are the risks of pica in horses?
Geophagia may be associated with an increased risk of sand colic; when large volumes of sand accumulate in the digestive tract leading to diarrhoea or intestinal impactions. Sand is most commonly involved. But any large quantities of rough soil may irritate the mucosal lining of the digestive tract. It is not unusual for horses to ingest small quantities of soil when grazing or when eating forage in the field; this can be reduced by moving sites where hay is given or by putting mats down. Dietary supplements such as Psyllium may help to reduce the risks of sand colic in some horses, but this is not a cure all. In horses that are known to eat mud or sand, other changes may be needed to reduce the risk of colic.
Intestinal parasitism is also a risk for any horse on pasture or in group housing. But those who engage in coprophagia may be in greater danger as they may have higher worm burdens due to ingestion of faecal material. As with all horses, regular faecal worm egg counts and tapeworm tests are recommended to check for infestations that may warrant treatment.
Treatment or prevention
It may not be possible to prevent pica in horses completely, however, there are some things that may help to reduce the frequency of this.
Provide adequate forage
Evidence suggests a strong direct correlation between low forge intake and pica. Ensuring that your horse has an adequate intake may help to reduce this behaviour. Forage is also critically important in the maintenance of gastrointestinal health. In general, horses need to consume 1.5-2% of their bodyweight in dry forage per day. This figure may change depending on energy needs; but diets containing below 1% bodyweight of forage can lead to an increase in stereotypical behaviours and medical problems.
As there is strong evidence to suggest that boredom may play a role in the development of pica, there are ways in which we can improve the horse’s environment to reduce this risk. Companionship with others, increased turnout or the provision of a window or mirror in their stable may help. Even spending more time with your horse, increasing ridden work or teaching them something new will all help to reduce boredom.
Hay bags or slow feeder nets are designed to reduce the speed at which the horse can extract hay from the net. And will increase the amount of time that your horse is occupied; giving less opportunity for stereotypical behaviours to develop. They are extremely helpful for all horses regardless of whether or not your horse demonstrates stereotypical behaviours. Horses have evolved to spend long hours eating, but often will finish their haynets quickly. Increasing the time spent eating will help to reduce spikes of blood glucose, which may improve general health. More time spent eating may reduce the drive to eat faecal material or bedding.
It is advisable to provide a salt lick specifically formulated for horses and most will make use of one. A readily available salt lick may reduce the incidence of pica. However, it should be noted that care must be taken with iron supplementation. Although iron has been shown to successfully treat pica in humans, most horses don’t benefit from iron supplementation. It may be detrimental to some as it is toxic to the liver in high doses. If in doubt, please consult your veterinary surgeon. If you are adding a salt lick to the diet, always ensure that fresh water is readily available at all times.
In conclusion, if your horse has recently started to consume soil or faecal material, it is always advisable to discuss this with your vet. They will be able to carry out a full clinical exam of your horse as well as being able to offer advice on diet and housing if these are potential causes of the problem.
- Horse enrichment activities | Blue Cross
- P.D McGreevy, L.A Hawson, T.C Habermann, S.R Cattle, Geophagia in horses: a short note on 13 cases, Applied Animal Behaviour Science, Volume 71, Issue 2, 2001,Aytekin, I., Onmaz, A.C., Aypak, S.U. et al. Changes in Serum Mineral Concentrations, Biochemical and Hematological Parameters in Horses with Pica. Biol Trace Elem Res139, 301–307 (2011). https://doi.org/10.1007/s12011-010-8660-y