Circulatory system of the horse
Encyclopedia
The heart
The equine heart is made of muscle tissue, more rounded in shape than a human's, built with the sole purpose of pumping blood throughout the body. It consists of 4 chambers: the left and right atria, and the left and right ventricles.The average adult horse has a 3.6 kg (8.5 lb) heart, although it can be more than twice this size (see "The X-factor" below). The heart grows until the horse is 4 years of age, although it can increase slightly in size with proper conditioning work. Heart size does not necessarily correlate to the size of the horse.
The blood and blood vessels
Blood is made up of red blood cells (erythrocytes) and white blood cells (leukocytes), as well as plasma. Produced in bone marrowBone marrow
Bone marrow is the flexible tissue found in the interior of bones. In humans, bone marrow in large bones produces new blood cells. On average, bone marrow constitutes 4% of the total body mass of humans; in adults weighing 65 kg , bone marrow accounts for approximately 2.6 kg...
, red blood cells are responsible for carrying oxygen to tissue and removing carbon dioxide, all via hemoglobin
Hemoglobin
Hemoglobin is the iron-containing oxygen-transport metalloprotein in the red blood cells of all vertebrates, with the exception of the fish family Channichthyidae, as well as the tissues of some invertebrates...
. White blood cells are used for defense against pathogen
Pathogen
A pathogen gignomai "I give birth to") or infectious agent — colloquially, a germ — is a microbe or microorganism such as a virus, bacterium, prion, or fungus that causes disease in its animal or plant host...
s in the immune system
Immune system
An immune system is a system of biological structures and processes within an organism that protects against disease by identifying and killing pathogens and tumor cells. It detects a wide variety of agents, from viruses to parasitic worms, and needs to distinguish them from the organism's own...
. Plasma suspends the blood cells, contains clotting factors, and contributes to the greatest volume of blood.
The heart and blood vessels contain approximately 34 Litres of blood in a 450 kg horse (9 U.S. gallons in a 1000 lb). Which equates to about 76 cc/kg (1.2 oz/lb)
The spleen
The spleen removes damaged red blood cells from circulation. It also holds extra blood cells, releasing them during exertion to increase blood volume and the amount of oxygen transported to tissues.The frog
Each hoof contains a structural component known as the "frog," which covers the deeper structure of the hoof known as the digital cushion, a vessel-filled tissue. When the horse places weight on a leg, the ground pushes upward on the frog, compressing it and the underlying digital cushion. This results in squeezing blood out of the digital cushion, which then helps to pump it back up the leg, helping the heart to work against gravity.Pulse
The average pulse is 28-45 beats per minute (bpm) in a mature horse, but it can reach more than 250 bpm during maximum exertion. This drops significantly within 15–30 seconds after the horse stops galloping. A 2-year-old horse may have a slightly faster pulse, and a 2-4 week old foal normally has a pulse between 70-90 bpm. Heart rate may also increase when the horse is excited, overheated or suffering severe dehydration, has a fever, has an infection or septicemia, has experienced a great deal of blood loss, has advanced heart or lung disease, or is in shock. In these cases, the resting heart rate may be above 80 in an adult animal. When the heart rate is below 20, the horse may be hypothermic, or have pressure on the brain, heart disease, or collapsed circulation.Determining heart rate
Heart rate may be determined with a stethoscope, placed just behind the left elbowHorse anatomy
Equine anatomy refers to the gross and microscopic anatomy of horses and other equids, including donkeys, and zebras. While all anatomical features of equids are described in the same terms as for other animals by the International Committee on Veterinary Gross Anatomical Nomenclature in the book...
of the animal. The pulse may also be felt when taken on an artery close to the skin, most commonly the facial artery located on the lower jaw just behind the cheek. The radial pulse may be taken right behind the back of the knee. The digital pulse is taken on the inside of the pastern, right below the fetlock. It is usually very faint and difficult to find, although certain problems, such as laminitis
Laminitis
Laminitis is a disease that affects the feet of ungulates. It is best known in horses and cattle. Symptoms include lameness, and increased temperature in the hooves...
, will make it quite strong.
Blood pressure
Although blood pressure may vary greatly between animals, the average blood pressure for a standing horse is 120/70 mmHg. An indirect measurement of blood pressure may be taken with a cuff placed around the middle coccygeal artery at the base of the tail, or above the digital artery. It is usually taken to monitor circulation during surgery. Direct blood pressure measurements, via catheterization of an artery provide a more accurate measurement, and are preferred for anesthetic monitoring.The gums
The gums of the horse can offer good clues in his circulatory heath. The owner can assess the gums by lifting the upper lip with one hand, while holding the head still (via halter) with the other.Gum color
- Pale pink: the healthy color of gums, indicates good circulation. May brighten slightly after stenuous work due to an increase in circulation.
- Very pale pink: due to contracted capillaries. May indicate anemia, fever, or blood loss.
- Pale blue, gray, or whitish: indicative of anaemia (low red blood cell count). May indicate severe shock or illness. A serious sign, often the best option is to call the veterinarian.
- Yellow with a tinge of brown: indicates jaundiceJaundiceJaundice is a yellowish pigmentation of the skin, the conjunctival membranes over the sclerae , and other mucous membranes caused by hyperbilirubinemia . This hyperbilirubinemia subsequently causes increased levels of bilirubin in the extracellular fluid...
and liver failure. Very serious and the veterinarian should see the animal immediately. - Yellowish: a bright yellow tinge may occur if the horse has high levels of beta-caroteneBeta-caroteneβ-Carotene is a strongly-coloured red-orange pigment abundant in plants and fruits. It is an organic compound and chemically is classified as a hydrocarbon and specifically as a terpenoid , reflecting its derivation from isoprene units...
in his diet, such as horses that eat a good deal of alfalfaAlfalfaAlfalfa is a flowering plant in the pea family Fabaceae cultivated as an important forage crop in the US, Canada, Argentina, France, Australia, the Middle East, South Africa, and many other countries. It is known as lucerne in the UK, France, Australia, South Africa and New Zealand, and known as...
hayHayHay is grass, legumes or other herbaceous plants that have been cut, dried, and stored for use as animal fodder, particularly for grazing livestock such as cattle, horses, goats, and sheep. Hay is also fed to pets such as rabbits and guinea pigs...
. Does not indicate any serious problem. - Dark red: indicates enlarged capillaries, due to poisoning or severe dehydration. The veterinarian should be contacted immediately.
Capillary refill time
The capillary refill time is determined by pressing a finger against the horse's gums for about 2 seconds, so that a white "thumbprint" is left. After releasing, it should take no longer than 2 seconds for the gum color to return to normal. If it takes longer for the gum color to return, the horse may be experiencing shock.The "X factor"
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Thoroughbred
The Thoroughbred is a horse breed best known for its use in horse racing. Although the word thoroughbred is sometimes used to refer to any breed of purebred horse, it technically refers only to the Thoroughbred breed...
, Quarter Horse
American Quarter Horse
The American Quarter Horse is an American breed of horse that excels at sprinting short distances. Its name came from its ability to outdistance other breeds of horses in races of a quarter mile or less; some individuals have been clocked at speeds up to 55 mph...
, and Standardbred racehorses. It was first documented in Eclipse
Eclipse (horse)
Eclipse was an outstanding, undefeated 18th-century British Thoroughbred racehorse who was later a phenomenal success as a sire.-Breeding:...
, known as an excellent broodmare producer, at 6.4 kg (14 pounds). A large heart was also seen in Phar Lap
Phar Lap
Phar Lap was a champion Thoroughbred racehorse whose achievements captured the public's imagination during the early years of the Great Depression. Foaled in New Zealand, he was trained and raced in Australia. Phar Lap dominated Australian racing during a distinguished career, winning a Melbourne...
(6.4 kg/14 lb), Sham
Sham (horse)
Sham , an American thoroughbred race horse, was one of the fastest horses of the 20th century, but was overshadowed by his larger-than-life peer and half-cousin, Secretariat. He was a dark seal brown in color. While racing, he wore green and yellow blinkers...
(8.2 kg/18 lb), and Secretariat
Secretariat (horse)
Secretariat was an American Thoroughbred racehorse, that in 1973 became the first U.S. Triple Crown champion in 25 years, setting new race records in two of the three events in the Series—the Kentucky Derby , and the Belmont Stakes —records that still stand today.Secretariat was sired by Bold...
(estimated at 10 kg / 22 lb). It is also thought that the great producing mare Pocahontas
Pocahontas (horse)
Pocahontas was an English Thoroughbred racehorse and the dam of three sires who had a great influence on the breed. Although mares are not generally considered to be as influential as sires, Thoroughbred Heritage refers to Pocahontas as "one of the most influential Thoroughbreds of all time, male...
was homozygous for the X factor. Large hearts have been traced back to four lines (all descendants of Eclipse): those of Princequillo
Princequillo
Princequillo was a Thoroughbred racehorse conceived in France and born in Ireland. He is known for his performances in long-distance races and his successes as a sire.-Background:...
, War Admiral
War Admiral
War Admiral was an American thoroughbred racehorse, the offspring of the great thoroughbred Man o' War and the mare Brushup. He inherited his father's fiery temperament and talent, but did not resemble him physically...
, Blue Larkspur
Blue Larkspur
Blue Larkspur was a bay Kentucky-bred thoroughbred race horse. He was inducted into the National Museum of Racing and Hall of Fame in 1957, awarded the 1929 Eclipse Award for Horse of the Year, and ranks Number 100 in Blood-Horse magazine's top 100 U.S. thoroughbred champions of the 20th Century...
and Mahmoud.
Because the X factor is found only on the x-chromosome, it may only be passed to a stallion's daughters, or to a colt or filly via his dam. This may explain why Secretariat had daughters that were better performers on average than his sons. Today, the hearts of racehorses are scored on a scale, and a high heart score can increase the animal's worth in some circles. That being said, poor training, conformation
Equine conformation
Equine conformation evaluates the degree of correctness of a horse's bone structure, musculature, and its body proportions in relation to each other. Undesirable conformation can limit the ability to perform a specific task. Although there are several universal "faults," a horse's conformation is...
, or attitude can make even the most talented athlete perform poorly.
Disorders of the circulatory system
- AnemiaAnemiaAnemia is a decrease in number of red blood cells or less than the normal quantity of hemoglobin in the blood. However, it can include decreased oxygen-binding ability of each hemoglobin molecule due to deformity or lack in numerical development as in some other types of hemoglobin...
- Arrhythmia
- Heart diseaseHeart diseaseHeart disease, cardiac disease or cardiopathy is an umbrella term for a variety of diseases affecting the heart. , it is the leading cause of death in the United States, England, Canada and Wales, accounting for 25.4% of the total deaths in the United States.-Types:-Coronary heart disease:Coronary...
- Heart failure