Why does my horse eat mud?

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 52 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.
Environmental enrichment
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 horses 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