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Equus caballus - Domestic Horse

Physical Characteristics:

Due to the extensive breeding of the domestic horse by humans there is a great deal of variation in body types. Dental formula is i3/3 c1-0/0-1 p3-4/3-4 m 3/3 with totals that vary from 36-44. Horses are quadruped and express unguligrade posture which is only the tips of the toes is in contact with the ground. This singular toe that takes the impact of movement is covered by a keratin shell. Facilitated by their need to escape predators main muscle mass has been moved up to the shoulder and chest area as is evident in Arabians and Quarter horses. The horse’s central body is composed of a barrel shaped chest that gives way to a long muscular neck developed for grazing. A large head rest at the end of the neck with 180 degree rotating ears and eyes set one either side. The entire body of the horse is covered by a dense hair which varies with different seasons. The crest of the horse’s neck is covered with 5-12 inch long course hair that is termed the mane. Also longer hair partially covers the animal’s forehead called the forelock. Coarse hair also extends from the dock which can grow all the way to the ground. In some breeds feathers around the fetlock are expressed (Reeder 1995).

Distribution in Wisconsin:

The modern horse, Equus caballus, has an immense distribution due to human’s dependence on it. Basically the distribution of the domestic horse in Wisconsin is dependent on humans. Very few individuals in this state depend on the horse as a work source. Primarily domestic horses are maintained in this area for the purpose of pleasure.

Ontogeny and Reproduction:

Puberty in female horses usually develop at about 18 months of age. Observed ovulation time is 4-8 days. Horses are seasonally polyestrous. A female signals her receptiveness to the stallion in a variety of actions. Holding her tail aloft to one side, urinating in short bursts, and winking of the labia are typical symptoms. If fertilization occurs, gestation is typically 335 days, around eleven months. Typically only one offspring is birthed by a mare in a single season. This gestation time allows the foal to be born in the spring when food is plentiful. Foals are born with the ability to remain at the mother’s side. Foal can walk within 20 minutes of their birth and their long legs allow for greater speed ability. Coprophagy has been observed in foals between the ages of four and six weeks of age. This action is an avenue for the foal to learn the food selective values of its mother (Alexander 1995). Weaning occurs typically, from 6-8 months but foals may remain by their dams for upwards of 2 years.

Stallions are aware of the female coming into estrous by the amount of estrogen present in her urine. The stallion sniffs the mare’s urine by drawing back his lips and scrunching up his nose. This action is termed the flehmen behavior. It has also been observed that the stallion will drink the mare’s urine (Reeder 1995).

Ecology and Behavior:

Wild horse herds express a harem social system in which one stallion resides over 5-20 breeding mares, including their foals and fillies. The stallion is the primary protector and the only male allowed mating privileges. As soon as young males mature they are chased off from the herd to eventually form herds of their own. Every herd has one head mare which conducts the group on its path and basically runs the herd. More often than not young females stay with the herd they are born to. In some instances though, young mares can be stolen by another stallion or just break off to join another herd.

With the domestication of horses also came the breakup of the herd system. Stables most often house horses separately either in stalls or paddocks, so not a great deal of the herd mentality is expressed. We can still observe the system of hierarchy among the members of a stable. If all members of a stable are maintained in one paddock we can readily observe this system during feeding time. One head mare receives the first right to eat and typically next are her daughters, if any are present in that paddock. Typically, young mares with no status, geldings, and new comers to the heard eat last and are continually chased off. There is also a hierarchy observed in separate paddocks with a mixture of males and females. Horses are grazing animals, primarily on grasses but in stable habitats they are, more often than not, feed hay and grain.

Principally most horses present in the world today are domesticated but they are a few herds that are still present wild. The Przewalski horse is located in the Gobi desert and retains some of the more primitive features such as a heavy set body, large head, long ears, and high set eyes. Australia is where the Brumby resides. The final wild horse is located in Eastern Europe and Russia and is called the Tarpan (Draper 2000).

Disease’s of Domestic Horses:

Eastern Equine Encephalitis originated from Uganda and the Middle East. Presently it is a life-threatening disease to the domestic horses of the United States. The primary vectors of this disease are mosquitoes species in particular Culiseta melanura (Center for Disease Control). The virus that is responsible for EEE is in the family Togaviridae, genus Alphavirus. Symptoms express themselves within 5-15 days and they can be 70-90% fatal (Minnesota Department of Health). Once infected, horses may show symptoms which include weakness, fever, convulsions, and partial paralysis. Symptoms may progress to seizures and coma which lead to death on most accounts (Minnesota Department of Health). As of 2002, seventy cases of EEE were reported in Wisconsin. Typically these cases were reported in the vicinity of swamps or wetlands.

Borrelia burgdorferi is commonly termed Lyme disease. Most commonly the vector for this disease is the deer tick. When infected only 10 % of horses express physical symptoms. A horse infected may express behavioral changes, stiffness in joints and may or may not show a fever. Behavioral changes are often due to the fact that they have joint stiffness (Center for Disease Control).

Literature Cited:

Alexander, A. J. and S.L. Marinier. 1995. Coprophagy as an Avenue for Foals of the Domestic Horse to Learn Food Preferences from their Dams. Journal of Theoretical Biology.
Center for Disease Control. 2003. Eastern Equine Encephalitis Fact Sheet.  <> . Accessed 28 Oct 2003.

Draper, J., S. Muir, D. Sly. 2000. Horse and Rider. Barnes & Nobles. New York.

Ellegren, H; A. Gotherstrom, J. Leonard, K. Liden, S. Marklund, D. Sandberg, C. Vila, R. Wayne. 2001. Widespread Origins of Domestic Horse Lineages. Science. Washington DC.

Minnesota Department of Health. 2003. Potential Risks of an Eastern Equine Enceplitis Outbreak. <> . Accessed 28 Oct 2003.

Reeder, D. M., and D.E. Wilson. 1993. Mammal Species of the World (second edition). Washington: Smithsonian Institution Press.

Reference written by Elizabeth Spiess, Biol 378:
Edited by Chris Yahnke. Page last updated 4-23-04.
©1993- University of Wisconsin-Stevens Point