Pica, or depraved appetite, refers to the eating of materials other than normal food. This behavior can range from licking to actually eating foreign substances, and can be classified according to the type of material involved. Some of the more common types are: osteophagia, the chewing of bones; coprophagia, the eating of feces; lignophagia, the chewing and eating of wood; and geophagia, the eating of soil or sand. These behaviors can lead to serious and even fatal digestive complications, and therefore should not be taken lightly.
The expression of pica behavior sometimes indicates an underlying health problem. This problem may be the lack of dietary bulk fiber, or the deficiency of individual nutrients such as salt, phosphorous and potassium. Chronic abdominal pain due to stomach and intestinal disorders and nervous system disturbances are also causes of pica. Frequently, a behavior begun in response to one of these conditions then becomes habitual.
Phosphorous deficiency most typically occurs in grazing animals in areas where the soil is very low in phosphorous, but it can occur in barn feeding as well. Affected horses may eat bone, wood, cloth, and other materials to which they have access. Phosphorous and iron deficiencies are known to induce soil eating, while potassium deficient animals may lick at wood and concrete. Sodium deficiency is more common in hot environments and in strenuously exercised animals, and induces salt seeking behaviors such as licking dirt and drinking urine.
Wood chewing horses seem to exhibit a desire for roughage or cellulose, as do animals who eat their bedding. By nature, horses spend much of their time grazing and if this activity is curtailed, such as when stabled, they are likely to seek other materials to consume. Lengthy periods of confinement, often combined with concentrated feeds that are quickly consumed, can cause boredom and lead to abnormal eating behaviors. Imbalanced rations, feeding at the wrong time of day and heavy worm burdens have also been found to contribute to this condition. Note that while in foals the eating of feces is so common as to be considered normal, it is abnormal in the adult. Adult horses who eat feces are typically stabled in loose boxes, and often have undergone a change in routine or management.
Control of pica behavior in horses requires close attention to all aspects of the diet. Feed analysis should be a routine practice, to aid in prevention of deficiencies and related pica behavior. Salt and mineral supplements should be made available at all times, and fresh feed such as grass, greens or carrots should be offered regularly. Feeding times should be consistent, with late night or early morning feeding being included in the schedule. Always provide hay when feeding concentrates, to fulfil grazing behavior as well as for balanced nutrition. Regular deworming is also recommended.
Once pica has been noted in an animal, steps must be taken to try and determine the underlying cause. Have your veterinarian examine the animal for anemia, worm burdens and possible mineral deficiencies, and provide appropriate treatments where indicated. If the animal in question has been on pasture, soil and forage analysis may be necessary to determine nutritional values. When health problems have been identified or ruled out, then measures can be taken to treat the behavior. Although it may be impossible to determine a direct cause of pica, through trial and error it is usually possible to find a method of treatment that controls the behavior.
Access to extensive pastures can help control pica in previously stabled horses, but the problem may still persist. Control of wood chewing can be attempted by regularly painting wooden surfaces with creosote. Including sawdust in a high concentrate diet can inhibit wood chewing, and can be considered as a control measure when access to pasture is limited. Horses who regularly eat soiled bedding or feces may have to be cross-tied. Confined animals should also be provided with enforced exercise. Control of pica may also be done by muzzling the animal, but the best remedy is to correct the underlying cause.
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Maynard, Loosli, Hintz and Warner. Animal Nutrition New York: McGraw Hill c1979
Naylor and Ralston. Large Animal Clinical Nutrition St. Louis: Mosby YearBook 1991