Horse Owners - MSD Veterinary Manual

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Veterinary Manual

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Description and Physical Characteristics of Horses

Horses have evolved over millions of years from animals about the size of dogs to the much larger size they are today. The origins of their association with people are unknown, but evidence suggests that they were first domesticated by nomadic Middle Eastern tribesmen around 2000 bc, or even earlier by the Chinese (3500 bc). Unlike dogs and cats, which are predators, horses are prey animals. They feed on grains and grasses and, like all prey animals of open grasslands, they tend to herd together for protection and take flight in response to danger or any unsettling circumstance.
- Introduction to Description and Physical Characteristics of Horses
- Description and Physical Characteristics of Horses
Selecting and Providing a Home for a Horse

Choosing the right horse takes time and can be difficult. Horses come in many different sizes, breeds, colors, temperaments, and states of health. All these things should be considered, while keeping in mind how the horse will be used (pleasure riding, barrel racing, showing, jumping, and other sports) and the rider’s skill and comfort level around horses.
- Selecting a Horse
- Providing a Home for a Horse
  - Housing
  - Diet
  - Exercise
Routine Care and Breeding of Horses

In addition to properly feeding and exercising your horse, other aspects of general care are needed to keep your horse healthy throughout his or her life. These include routine veterinary care for vaccinations, parasite control, and dental care; grooming and hoof care; and protection from the elements.
- Routine Health Care of Horses
- Breeding and Reproduction of Horses
  - Foal Care
Behavior of Horses

Behavioral medicine is the scientific study of everything animals do, whether the animals are insects, birds, mammals, fish, or humans. The field of animal behavior is concerned with understanding the causes, functions, development, and evolution of behavior. Behavior refers to the actions or reactions of an animal. Behavior is controlled by the endocrine and nervous systems. The complexity of an animal’s behavior is related to the complexity of its nervous system. Generally, animals with complex nervous systems have a greater capacity to learn new responses and thus adjust their behavior.
Blood Disorders of Horses

Blood cells form and develop mostly in the bone marrow, that is, the tissue located in the cavities of bones. Blood performs a variety of important functions as it circulates throughout the body. It delivers oxygen and vital nutrients (such as vitamins, minerals, fats, and sugars) to the body’s tissues. It carries carbon dioxide to the lungs to be exhaled and waste products to the kidneys and liver to be eliminated from the body. It transports hormones, which are chemical messengers, to various parts of the body, allowing those parts to communicate with each other. Blood also includes cells that fight infection and platelets that control bleeding.
Bone, Joint, and Muscle Disorders in Horses

The musculoskeletal system includes the bones, cartilage, muscles, ligaments, joints, tendons, and other connective tissue. It supports the body, permits movement, and protects the vital organs. Because many other body systems (including the nervous system, blood vessels, and skin) are interrelated, disorders of one of these systems may also affect the musculoskeletal system.
Brain, Spinal Cord, and Nerve Disorders of Horses

The nervous system is made up of the brain, spinal cord, and several kinds of nerves that are found throughout the body. These create complex circuits through which animals experience and respond to sensations.
Digestive Disorders of Horses

The digestive system includes all of the organs that are involved in taking in and processing food. It begins with the mouth and includes the esophagus, stomach, liver, pancreas, intestines, rectum, and anus.
Ear Disorders of Horses

The ear is an organ of hearing and an organ of balance. It consists of the outer, middle, and inner ear.
Eye Disorders of Horses

The eyes of animals, including the eyes of horses, function much like your eyes. Animals also develop many of the same eye problems that people can have, including cataracts, glaucoma, and other problems. Because sight is the way in which horses get the majority of their information about their surroundings, it is important for your horse to receive good eye care to protect its sight and allow the horse to interact comfortably with its environment. In general, horse vision is a little blurrier and a little less colorful than human vision. However, horses see movement very well throughout the 340° arc of their peripheral vision. This means a horse can see movement in most areas around its body, even with its head facing forward.
Heart and Blood Vessel Disorders of Horses

The cardiovascular system includes the heart and the blood vessels—the veins and the arteries. The function of the heart is to pump blood. The right side of the heart pumps blood to the lungs, where oxygen is added to the blood and carbon dioxide is removed from it. The left side pumps blood to the rest of the body, where oxygen and nutrients are delivered to tissues, and waste products (such as carbon dioxide) are removed. In horses, the cardiovascular system must not only efficiently supply blood to all parts of a large animal, but must also function well during strenuous racing or training, in many cases.
Hormonal Disorders of Horses

Hormones are chemical messengers that have many different functions. The effects of hormones in the body are wide-ranging and varied. Some familiar examples of hormones include insulin, which is important in the development of diabetes, and estrogen and progesterone, which are involved in the female reproductive cycle.
- Introduction to Hormonal Disorders of Horses
Immune Disorders of Horses

The immune system consists of a network of white blood cells, antibodies, and other substances that fight off infections and reject foreign proteins. In addition, the immune system includes several organs. Some, such as the thymus gland and the bone marrow, are the sites where white blood cells are produced. Others, including the spleen, lymph nodes, and liver, trap microorganisms and foreign substances and provide a place for immune system cells to collect, interact with each other and with foreign substances, and generate an immune response.
Kidney and Urinary Tract Disorders of Horses

The urinary system or tract includes the kidneys, the ureters (tubes that connect the kidneys to the bladder), the bladder, and the urethra (the tube through which urine exits the body). The urinary system has several important functions. It gets rid of the waste products that are created when food is transformed into energy. It also maintains the correct balance of water and electrolytes (salts) within the body. Another key function is the production of hormones called erythropoietin and renin, which are important in maintaining healthy blood pressure, producing blood cells, and absorbing salt correctly. Finally, the urinary system processes vitamin D to its active form.
Lung and Airway Disorders of Horses

The respiratory system consists of the large and small airways and the lungs. When a horse inhales, the air travels down the trachea, which divides into the tubes known as the right and left bronchi, then into the smaller airways called bronchioles in the lungs. The bronchioles end in the small sacs called alveoli, where the barrier between the air and the blood is a thin membrane.
Metabolic Disorders of Horses

Metabolism refers to all processes in the body that break down and convert ingested substances into the energy and nutrients needed to sustain life. Foods, liquids, and drugs all undergo metabolic processes within the body. Many foods are complex materials that need to be broken down into simpler substances, which in turn become “building blocks” for the body to use as needed. For example, protein is broken down into amino acids, which are used to build new proteins and regulate key metabolic reactions. Enzymes, are proteins that stimulate biochemical reactions for many metabolic processes. Whenever the function of an enzyme is altered, a metabolic disorder can develop. Metabolic disorders are important because they can affect energy production or damage tissues critical for survival. They may be inherited or acquired. Acquired metabolic disorders are more common and significant. Metabolic disorders may result in a substance rising to toxic levels (a storage disorder), or a necessary substance may not be produced, causing a deficiency.
Reproductive Disorders of Horses

The reproductive system is the group of organs that produce offspring. In both males and females, the reproductive system is composed of primary sex organs and primary regulatory centers. The primary sex organs are the testes in males and the ovaries and uterus in females. The primary regulatory centers are in the brain. They control the production of hormones that in turn influence the function of the primary sex organs.
Skin Disorders of Horses

The skin is the largest organ of your horse’s body. It provides a protective barrier against the environment, regulates temperature, and gives your horse its sense of touch. Depending on the species and age, the skin may be 12 to 24% of an animal’s body weight. The skin has 3 major layers: the epidermis or outermost layer, the dermis or middle layer, and the subcutis or innermost layer. Other important components include skin appendages (such as hair and hooves), and subcutaneous muscles and fat.
Disorders Affecting Multiple Body Systems of Horses

There are many disorders or conditions that can affect multiple parts of the body. These disorders and conditions may be caused by bacteria, viruses, poisonous or toxic substances in the environment, and other health hazards. Disorders affecting multiple body systems can also be inherited or can develop while the animal is still in the womb. Any disorders or conditions that involve multiple organ systems are described as systemic or generalized.

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