Horse Anatomy: The Skeleton Overview

The Skeleton

• The horse's skeleton provides support, protects vital organs, gives muscles somewhere to attach, and stores minerals like calcium, phosphorus, magnesium, sodium, and potassium.
• Bones are constantly remodeling themselves based on stress, diet, and blood supply.
• Bones can be classified as dense or spongy, and can be long, short, flat, or irregular.
• The surface of the bone is covered with a tough membrane (periosteum) and cartilage is between bones.
• A horse has approximately 205 bones that are divided into the axial and appendicular skeletons.

Axial Skeleton

• The skull consists of 34 bones and four cavities: cranial cavity, orbital cavity, oral cavity, and nasal cavity.
• Red blood cells carry oxygen to tissues and remove carbon dioxide, white blood cells defend against pathogens.
• Plasma, the liquid element of blood, contains water, protein, glucose, lipids, salts, enzymes, hormones, and antigens.
• The heart, approximately 3.6-4kg, has four chambers: left atrium, right atrium, left ventricle, and right ventricle.
• Blood enters the left atrium, then the left ventricle, then travels through the aorta to the body.
• A horse's heart keeps growing until they are around 4 years old.
• Arteries carry blood from the heart, veins carry blood to the heart.

Cardiovascular System

• The heart rate of a horse at rest is 28-45 beats per minute.
• Heart rate increases during exercise, excitement, nervousness, dehydration, fever, infection, or shock.

Lymphatic System

• The lymphatic system supports the immune system and is composed of lymph nodes and lymph vessels.
• The lymphatic system is a waste removal system that also recovers, filters, and recycles tissue fluid.

Digestive System

• Digestion starts with the teeth, horses have 36 permanent teeth.
• Horses tear grass with their incisors, it is then pushed between the molars where it is broken down.
• Food is then mixed with saliva and swallowed, passing the larynx to the esophagus, and then to the stomach.
• The stomach can only hold 12 liters of food, overload can lead to colic.
• Horses do not vomit, because the stomach only allows food in.
• Horses produce bile but do not have a gall bladder.

Nervous System

• The nervous system is composed of the brain, spinal cord, nerves, nerve fibres, and nerve cells (sensory and motor neurons).
• The brain is protected by the bones of the skull and the meninges, which also provide nutrients.
• The brain is divided into three areas: forebrain, midbrain, and hindbrain.

Endocrine System

• Hormones, secreted by the endocrine system, regulate growth, reproduction, digestion, and other body functions.
• The endocrine system is made up of: hypothalamus, pituitary gland, thymus, thyroid gland, parathyroids, pancreas, adrenal glands, ovaries, and testes.

Sensory Systems

• Horses are very sensitive to touch, with sensitive skin covered in receptor cells.
• The muzzles have tactile hairs and vast numbers of nerve endings.
• The skin is divided into three layers: epidermis, dermis, and subdermal layer.
• Horses have a much better sense of smell than humans.
• Horses “flehmen” to amplify a smell, not show distaste.
• Horses have large, mobile tongues but little is known about their sense of taste beyond bitter, sweet, sour, and salty.