Has your horse started eating or licking the soil? The ingestion of soil in animals is referred to as geophagia.
The reason some horses eat dirt is not fully understood. But the behavior is thought to serve a nutritional purpose by providing minerals and other nutrients that might be lacking in the diet. 
Geophagia may also be linked to boredom or stress.  Horses may nibble on the soil to pass the time, relieve anxiety, or alleviate stomach pain.
Geophagia can be harmful because the soil may contain parasites and other pathogens that cause illness.  Excessive ingestion of dirt can also damage the intestines and lead to impaction colic.
You can help to prevent your horse from practicing geophagy by providing them with a healthy forage-based diet that meets their nutritional needs.
If your horse is ingesting dirt, consult with your veterinarian to rule out any underlying medical causes and to develop a management plan to help redirect this behavior.
Why is My Horse Eating Soil?
Geophagy, also referred to as geophagia, is a behavior that involves eating dirt.  The condition has been observed in domesticated and wild horses and in other species including camels, buffalo, and sheep. 
This condition is a form of pica, the craving for and consumption of non-food items.  Horses may also be seen eating tree bark, wood (lignophagia), bedding, hair and manure (coprophagy).
Some expressions of geophagy may be an example of stereotypic behaviors, which are repetitive behaviours expressed to alleviate stress or boredom.
However, in some horses, the licking or eating of dirt does appear to serve a purpose. Horses may engage in geophagy because they are seeking one or more nutrients in the soil that are missing in their daily diet. 
In other species, pica is associated with amino acid deficiencies, vitamins and trace mineral deficiencies, a lack of alkaline substances, or imbalances in minerals such as the calcium to phosphorus ratio. 
Seeking Nutrients in Soil
Wild horses have been seen visiting the same sites repeatedly to ingest soil from specific areas. Domesticated horses have been observed performing the same behavior in paddocks and yards. 
The sites that horses visit when engaging in geophagia are typically small in area and returned to on multiple occasions.  Their return to the same sites suggests the locations are associated with a resource that may provide a physiological benefit. 
Research also shows that areas in which horses engage in geophagia tend to contain higher levels of iron and copper in the soil compared to control sites. 
Mineral deficiencies could explain why some horses eat soil, including diets that are lacking in the following minerals: 
Signs of Geophagy
Many horse owners become aware of geophagy by observing their horse repeatedly eating soil when turned out. But even if you don’t see your horse eating soil, a few key signs indicate a horse is engaging in geophagy.
Abnormal Particles in Manure
The presence of dirt or other foreign objects in the manure provides evidence that your horse is ingesting substances other than their regular feed.
If your horse is observed licking or biting the ground, it may indicate that they are ingesting soil.
According to a study on the feeding habits of 35 horses across 13 sites, owners reported that 30 horses (86%) licked at the soil, 24 (69%) pawed at it, and 23 (66%) used their teeth on the soil. 
Changes in Eating Habits
Pay attention to any changes in your horse’s eating habits. Horses with geophagy may consume less hay and grain than normal if they are eating soil.
Geophagia is a relatively common behavior in horses, but if left unchecked it can lead to complications in the digestive tract including parasites, blockages and nutritional deficiencies.
Soil can contain harmful bacteria and parasites that can cause intestinal illness and infection. 
Some of the most common internal parasites include large strongyles, small strongyles, roundworms, tapeworms, pinworms, and bots.
These parasites can cause weight loss, diarrhea, anemia, hair loss, and colic, and transmit diseases to horses such as Cryptosporidiosis and Giardiasis.
Ingesting large amounts of soil, stones and debris can lead to blockages in the gut. In severe cases, surgery may be required to remove the blockage.
Complications can include constipation, cramping, colic, loss of appetite, pain, obstruction, diarrhea, weight loss, and perforation from sharp objects such as rocks or gravel. 
Geophagy may deplete the body of important nutrients and minerals, leading to poor health and decreased performance. 
Ingesting excessive amounts of soil and clay may result in secondary nutrient deficiencies by inhibiting the absorption of dietary iron. Soil binds to iron complexes and decreases the uptake of this macromineral from the intestines. 
Ingesting soil in a sandy area presents a health hazard due to sand colic.  This condition occurs when ingested sand accumulates in the horse’s intestines forming a hard, compacted mass.
If left untreated, sand colic can be fatal.
You may be unsure why your horse is ingesting soil, but it is important to determine the cause of geophagy to prevent the behaviour from continuing.
The causes of geophagia are often difficult to identify but may involve:
1) Nutritional Deficiencies
Horses may lick, bite or eat soil in response to a dietary deficiency. The location where horses eat soil and the timing of when horses engage in geophagy may reflect their need for certain nutrients.
Anecdotally, geophagy is said to occur primarily in horses returning to pasture in the spring. These horses are transitioning from consuming hay to spring grass after not having access to pasture or being stabled for the winter. 
Sodium deficiency is believed to be a primary cause of soil ingestion in horses.  Sodium is an important electrolyte and plays a role in thirst regulation, fluid balance, muscle contractions and nerve signal transmissions.
Horses appear to have nutritional wisdom regarding their need for salt (NaCl or sodium chloride). When levels are low in the diet, they naturally seek out and voluntarily consume higher amounts of salt. 
A study comparing blood nutrient levels between 15 healthy horses and 15 horses with geophagy found that the serum concentrations of iron were lower in horses with the condition than in healthy animals. 
In this study, the iron-containing oxygen-transport protein, hemoglobin, was also lower in horses with pica but still within a normal physiological range compared to healthy horses. Low hemoglobin can be caused by iron deficiency. 
Geophagy is thought to contribute to iron deficiency because soil and clay can bind dietary iron complexes and decrease the absorption of iron through the intestinal wall. 
Research shows an association between a form of geophagy known as pica and iron deficiency in humans. In many cases, pica can be treated effectively by correcting depleted iron levels. 
Low copper intake is also associated with geophagia.  In the study previously mentioned, blood concentrations of copper were lower in horses with pica compared to those without the condition. 
This study also noted that the copper to zinc ratio was lower in horses with pica compared to those without the condition. 
Copper plays an important role in transporting iron across membranes and into circu