Dirt-eating, phosphorus deficiency and pica
Recent cases involving dirt-eating are a timely reminder to revisit the question "why is my horse eating dirt?" An abnormal appetite for unusual items is termed pica, and may include eating dirt, wood, bones, tails, dung, or other inanimate objects. The two most common forms of pica seen in horses are eating dirt and chewing or eating wood.
Phosphorus deficiency is the main cause of dirt-eating in our area. Cases generally occur in the late summer/autumn period and are more common in drier years. The decrease in both quantity and quality of pasture under these conditions can result in low phosphate intake, even when soil phosphate levels are normal. If low blood phosphate levels result, innate behaviour can lead to horses eating, or even craving, dirt. Other clinical signs of phosphorus deficiency are decreased appetite, loss of coat lustre and colour, loss of condition, lethargy and poor performance in athletic animals.
Blood testing is important in horses showing clinical signs of phosphorus deficiency as not all deficient horses will eat dirt. Conversely, not all horses eating dirt have low blood phosphate levels. If adequate phosphate is supplied from the dirt, other deficiencies or diseases may be the cause.
Phosphorus deficiency may also be seen in the spring as a result of soil-leeching during wet winters. This can be an important cause of poor performance in athletic animals at this time of year. Dirt-eating is not a feature of this form of deficiency.
Phosphorus supplementation generally quickly corrects dirt-eating and other signs of deficiency.
Low grade wood-chewing is usually a stereotypy (an habitual behavioural problem) and occurs throughout the year. The epidemics of wood-chewing and eating seen in late autumn/early winter probably involve nutritional imbalances or deficiencies.
All cases of pica should be investigated, particularly when accompanied by loss of condition, poor performance or changes in behaviour. If you have concerns about your horse's appetite, call one of our equine vets to assist with the investigation.
