The Anatomy and Physiology of Horses
Anatomy refers to the form and structure of organisms. In comparison, physiology is the study of the functions of the body and its parts. Physiology looks at the body systems, organs, tissues and cells.
A horse’s anatomy includes its skeletal system, muscles, the brain and nervous system, all internal organs and the hair and skin. (See Figure 2.2) Thorough and detailed information on horse’s anatomy and physiology can be found in “Parts of the Horse” in the 4-H Horse Reference Manual.
A horse owner has a responsibility to know and understand their animal’s anatomy and physiology.
Skin & Hair
The skin is the horse’s largest organ and makes up between 12 and 24 percent of the animal’s total weight, depending on its age. The skin has many functions:
- It protects underlying tissues from injury, drying, water absorption and bacteria.
- It regulates the body’s temperature.
- It excretes water and salts through sweat glands, senses the environment and synthesizes vitamin D when exposed to sunlight.
The hair also provides protection as well as warmth in the winter and cooling in the summer. The hair filters ultraviolet light. Horses can lose large amounts of water through sweat, so a constant supply of clean, fresh water is important.
The horse has unique eyes – they are both monocular and binocular. Monocular means that the horse can see objects with one eye. As a result, the brain often gets two images simultaneously. With binocular vision the horse can focus with both eyes and the brain receives only one signal. People only have binocular vision and see with both eyes at the same time.
A horse’s eyes should be bright. The membranes surrounding the coloured portion of the eye should have a healthy soft pinkish colour and appear moist. If there is infection or inflammation these membranes become bright pink and inflamed. Poor blood circulation to the membranes, such as during shock, will cause them to appear almost white. During an illness the eyes may appear to sink back into the skull, usually due to dehydration.
The skeleton gives the horse its physical structure. The structure of a horse’s skeletal system and the angles at which its bones connect determines the horse’s physical capacity and athletic potential. Joints and ligaments allow the horse to move smoothly.
A horse has the same requirements for water, energy, protein, vitamins and minerals as do all animals but differs in the type and function of its digestive system. The horse falls between a ruminant and non-ruminant. Non-ruminants (humans, pigs and dogs) digest carbohydrates, protein and fat by enzymatic action. Ruminants (cattle, sheep and deer) use bacteria in the fore stomachs to digest fibre by fermentation and use enzymatic digestion in the small intestines.
The horse’s foregut includes the mouth, esophagus, stomach and small intestine. The hindgut includes the large colon small colon and rectum.
A horse’s stomach can hold only about 8 to 15 litres. The food passes through the stomach into the small intestine and then to the cecum, large intestine and colon, called the hindgut. The process of fermentation, which allows horses to break down cellulose, takes place in the hindgut of the horse. This system allows the horse to digest simple carbohydrate sources such as starch from grain in the foregut. Fibrous sources such as oat hulls, soy hulls, beet pulp, hay and pasture are digested in the hindgut. The small intestine is where the nutrients from carbohydrates are absorbed. Nutrients from fibre in the diet are absorbed in the hindgut.
The sounds made by the gut in the flank of the horse can provide indicators of health. Gut sounds is the term used for the noise heard as food and water moves down the gastric intestinal track. You should hear intermittent gut sounds two to four times a minute.
Abnormal or no gut sounds at all can indicate an intestinal blockage or a twist of the gut, which may be very dangerous. This is called colic. High pitched frequent sounds can indicate a gas build-up, which can also be a sign of colic.
Above information used with permission from:
- Equine Digestive Tract Structure: Ontario Agriculture, Food and Rural Affairs
- Equine Vital Signs (Western Horse Review: May 2011)
- Horse Council British Columbia’s HCBC Basic Horse Care Booklet