THE HORSE
CLASSIFICATION
Kingdom
Phylum
Class
Order
Family
Genus
Species
Animal
Chordata
Mammalia
Perissodactyla
Equidae
Equus
caballus
TERMINOLOGY
Mare
Stallion
Stud
Foal
Colt
Filly
Gelding
Ridgling
Mature female horse over 3 yrs of age
Mature intact male over 3 yrs of age
Usually refers to a purebred stallion
A young horse male or female up to one year of age
Intact male horse from 1 to 3 yrs of age
A young female horse from 1 to 3 yrs of age
A castrated male horse
A male horse with one testicle that has not descended
HISTORY
The actual evolution of the horse is a long and complicated path but it can be
generally agreed upon that the modern day horse probably evolved from Przewalski’s
horse. Przewalski’s horse is the only real “wild” horse, most wild horses are tame horses
that have returned to their feral nature. There are three species of zebra and two species
of ass that are also considered wild horses but they are much more distantly related to the
modern horse. Fossil evidence pegs the evolution of the wild horse at about 1.5 million
years ago.
Horses are different from most other domesticated animals in that they are used
more for pleasure rather than for meat or as a source of draught power. When the horse
was first domesticated around 2500 BC. the willingness of the horse to be trained led to
its use as a source of transportation. The speed and agility of the horse helped people
travel and gave them an advantage during battles. The range of the horse was
instrumental in helping invaders cross Europe and conquer their foes. Even the early
settlement of the wild west would have been a lot different without the help of the horse.
With the invention of the combustion engine in the early twentieth century the
importance of the horse declined. Cars and trucks quickly replaced the horse as a means
of transportation and the need for draught power was also eliminated. Horses no longer
needed by the working class became a prestige animal and were mostly owned by
wealthy people that used them for pleasure rather than work. Fox hunting, show jumping
and racing all became upper class activities that relied on the horse. Horses today are
more than ever a recreational animal used for polo games, pleasure riding and rodeos.
The difference today is that the enjoyment of horses is no longer restricted to the wealthy
people. There still remains a few animals that are used for herding purposes or for
pulling but the majority are trained for pleasure purposes.
STATISTICS
Lifespan
Body weight (adult)
Ponies
Horses
Body Temperature
Heart rate
Respiration
20-30 yrs
200-300 kg
500-1000 kg
38 C
35-45 beats/min
8-12 breaths/min
BEHAVIOR
Horses like most other animals are somewhat social and enjoy and depend on the
interaction with others of its own kind. In the wild horses will form bands of either
family members or of bachelor males. These bands are closely knit groups that may
loosely associate with other bands that share the same territory forming a herd of horses.
All the different types of bands will have a social dominance hierarchy in place. In an all
female band the most dominant member is usually the oldest mare. In a band with a
stallion and harem the male is usually the dominant horse. In the two above groups the
bands’ social hierarchy is very stable and there will be very few challenges for
dominance. In an all male band there is constant jockeying for position and many
physical as well as behavioral challenges take place to determine the pecking order of the
group.
Domesticated horses seem to develop behavioral problems much more often than
any other farm animal. It is probably because we have a much more social or personal
relationship with horses that we try to understand what the animals’ different behaviors
mean. Certain behaviors like stretching, mutual grooming and exploration are all
considered normal and play important roles in the horses well being. While behaviors
like cribbing (chewing wooden boards or gates), polydipsia nervosa (consuming
abnormal amounts of water) and weaving are indicators that the animal may be stressed
or bored and may be physically or mentally unwell. Horses that are often stabled for long
periods of time or do not get enough exercise are prime candidates for developing
abnormal behavior. Knowing the normal behavior of a horse is very important so that
abnormal behavior can be recognized and then treated. There are lots of good books
dedicated to the behavior of horses but spending time with the animal is probably the best
way to learn what is considered normal behavior and what may be abnormal.
ANATOMY AND PHYSIOLOGY
Dentition
Horses have 3 upper incisors and 3 lower incisors that are used to nip and tear
grass and hay. The 6 upper and 6 lower cheek teeth are used for grinding the course plant
material and are known as hypsodont. Hypsodont teeth are fully formed in the young
horse and slowly erupt over the life of the horse as the teeth are worn down. Because the
teeth are continually growing this can lead to uneven wear and very sharp, elongated
ridges called points and hooks can occur. These points and hooks can cut and pierce the
cheeks, tongue and gums of the horse and should be periodically removed. The sharp
edges are filed down with a special rasp called a float, this procedure is called floating
the teeth.
The first upper premolar may or may not be present in the horse. If it is present it
is very small and will not come into wear because there is no tooth opposite on the lower
jaw. This tooth is called a wolf tooth and is often removed so that it does not come in
contact with the bit when the horse is bridled.
Digestive System
Horses are monogastric meaning they have only one stomach, unlike the cows
and sheep that have 4 stomachs. Horses are herbivores that derive their nutrients from
plant material only. The horse by itself is unable to unlock the energy of cellulose and
depends on microbes to digest the plant material. Horses are known as hindgut
fermenters because the breakdown of cellulose occurs after the stomach. Microbes are
present in the colon to breakdown cellulose into glucose and volatile fatty acids as well as
vitamins B and K.
Thermoregulation
Horses that live outdoors at all times will change their coat twice a year. In the
fall a thick, long winter coat is grown and in the spring the winter coat is shed leaving a
short, thin summer coat. The large body of the horse allows it to withstand very low
temperatures and as long as they have a good, ad lib source of food most horses can
withstand even our cold winters. If a horse is to remain outside for the winter the coat
should not be groomed as this would remove secretions that help to keep the animal
warm and dry. Horses that are still worked or ridden during the winter are usually
clipped of the long winter coat so they do not overheat while being exercised. The
clipped horses are then outfitted with a coat or rug that helps to conserve body heat and
the animal can still spend time outdoors without fear of hypothermia.
The thermoneutral zone of horse covers quite a wide range from –15 C to +10 C.
Horses can also survive in relatively warm environments due to some physiological as
well as behavioral techniques. Horses have sweat glands so they are able to lose some
heat in warm conditions through evaporation. The horse will also seek shade and try to
find a windy area to help cool the body. Giving the horse less hay and more grain in the
diet will produce less heat during the digestion process.
Reproduction
Mares will first start to show signs of estrus when the reach puberty (18-24
months old) and will continue to cycle throughout their lifetime. Most mares (80%) are
seasonally polyestrus meaning they will ovulate many times during the spring to
summer breeding season and then go into a period of anestrus (not ovulating) during the
winter months. The increasing daylight and temperatures seems to play the biggest role
of bring a mare into estrus. Colts that are in good health and body condition will have
functioning testes at 2 years of age and will start to produce sperm. Usually older
stallions are used for breeding purposes so as to increase the chances of fertilization.
An estrus cycle will occur every 21 days during the breeding season and the mare
will be receptive to the male (in estrus) for 5-6 days. Once a mare is bred she will be in
foal or gestating for 11 months. 7-9 days after the foal is born the mare will come into
heat, known as the foal heat. If the mare is not bred on the foal heat she will begin the
21day cycle either until she is bred or goes into anestrus in the fall. In the wild or in
domestic herds with a stallion always present a mare is almost always pregnant. Having
the breeding season in the spring ensures that the young is born at a time of year when the
weather is getting nicer and the pastures are growing.
Being able to detect when a mare is in heat is much more difficult than in cattle.
Most mares will not show any signs unless in the presence of a male when they may
squat, raise their tail, urinate and evert the labial vagina (winking). It is thought that
winking may help spread a phermone from the surrounding tissue that helps attract the
stallion. Teaser stallions may be used to help detect which mares are in heat. The teasers
are not allowed in with the mares but even across a fence the stallion is able to detect
which females are cycling and will usually cause the mare to demonstrate her signs of
readiness. The stallion exhibits the Flehmen response when checking mares to see if
they are in heat. Courtship can seem aggressive with both the mare and stallion nipping
and kicking at each other but once the female is ready to be mated she will stand still
while the stallion mounts her.
There are three methods of breeding tame horses each with their own advantages
and disadvantages:
1) Hand Breeding: Once a mare has showed signs of estrus she is restrained or
hobbled and made ready for the stallion (tail tied and labia washed). The
stallion is brought on a halter to the mare. Once the stallion has determined
the mare is ready for breeding he is allowed to mount the mare. This method
prevents injuries from occurring to the stallion and mare but increases the
chance of injury to the people that are holding the mare and stallion. Biting
and kicking can all be part of the breeding process so caution and safety
equipment should always be used when around breeding horses. This method
has good conception rates and allows for accurate foaling dates.
2) Artificial Insemination A.I. : Teaser stallions are used to determine when the
mare is in heat and then she is brought into a holding area. The stallions
semen is deposited directly into the uterine body by a trained technician and
this will usually ensure higher conception rates than hand breeding where the
semen is deposited in the vagina. There is no stallion present so injury to the
mare and to people is greatly reduced though the mare may need to be
hobbled if she tries to kick. Horse semen can not be frozen as it destroys the
sperm but a relatively new process to chill the semen allows the transport of
semen around the country so certain studs can be used all over the country.
Unfortunately not all breed associations accept A.I. as a method for breeding
so some breeders are limited to their access to studs.
3) Pasture Breeding: A proven stallion is always present with a herd of mares.
The stallion breeds the mares as they come into heat. With this system there
is no way to predict when foals are going to be born, the chances of injuries
occurring to the horses is increased and the conception rate is the lowest of the
three methods. About the only advantage of this system is that no human
labor is required for breeding to be achieved.
If the mare does not come back into heat after breeding she is most likely
pregnant, this can be confirmed by doing a rectal palpation, ultrasound or blood test.
When the mare is close to giving birth her udder will fill up, colostrum may be present on
the ends of the teat (waxing), and she will become restless. As labor progresses there
may be a release of fluid from the vulva as the first water bag (the allantochorion) bursts
as it passes through the cervix. The front hooves are the first part of the foal to arrive
with the head extended on the forelimbs coming next. The foal is usually born inside the
second water bag (the amnion) that will burst as the foal passes into the outside world.
The afterbirth will be passed 3 to 6 hours later and the mare does not eat the afterbirth
like most other mammals do. The foal is able to stand 1 to 2 hours after birth and should
suckle shortly thereafter. The colostrum is only absorbed for the first 12 hours of life and
it is very important that the foal has received the colostrum in this time.
Breeding age
Length of estrus cycle
Duration of estrus
Breeding life span
Gestation length
Average birth weight
Age at weaning
18-24 months
21 days
5-7 days
25-30 years
320-360 days
40-60 kg
6-7 months
Senses
Horses in ancient times were prey animals for a number of different large
carnivores. This may be the reason for the horses well developed sense of smell and
vision. A horse can almost see 360 degrees in the horizontal plane, there is a small blind
spot (about 5 degrees) directly behind the horse. A horses’ binocular vision that allows it
to see in 3D and judge distances is an arc of about 70 degrees directly in front of the
horse. Horses can see better in low light and at longer distances than humans can but the
ability to see color and judge distances is much stronger in humans. It seems the horses’
eye has developed to be able to detect predators from great distances.
Horses have an extensively folded sensory area found at the back of the nasal
cavity that is known as the cribriform plate. The highly sensitive area allows the horse
to have a much more extensive sense of smell than we do. There sense of smell probably
alerted the horse to the presence of predators long before they could see them. Horses
have a highly developed vomeronasal organ that enables the animal to sense certain
chemicals such as phermones in the air. The Flehmen response (curling of the upper
lip) traps odors in the vomeronasal organ and allows the horse to sample the air. The
vomeronasal organ may also allow the horse to sense the chemicals associated with fear
or alarm and cause the horse to become anxious or stressed.
Hearing is not a very important sense in the horse as they depend much more on
olfactory and visual cues as a means of communication. The auditory signals that are
used by horses are usually quite loud and easy to pick up. Squeals, whinnies, neighs and
knickers are all sounds that travel long distances and are quite loud. The ears of the horse
have a good range of mobility but the horse still has trouble locating the source of a
sound. Humans are able to pinpoint within one degree where a sound is coming from
while a horse has a threshold of about 25 degrees when locating a sound.
The sense of taste in the horse seems to be as individual as it is in people. Some
horses really like sweet tastes while others enjoy something saltier. It is thought that
nutritional status, electrolyte status, previous experience and individual preference has
more to do with the food, water and minerals that a horse searches out rather than on taste
alone.
The sense of touch in horses may be a relatively important sense when it comes to
relationships amongst horses as well as with people. Grooming a horse will actually
release soothing chemicals and relax a horse, even decreasing the heart rate. Grooming
between horses is often seen and may be part of maintaining the social bonds between
horses. People groom their horse not only for the health of the animal but also to develop
a bond and trust between the two.
HUSBANDRY AND ENVIRONMENT
Housing
The easiest way to house horses is to let them out into a pasture that has a clean
source of water and lots of lush vegetation to eat. If horses are to be on the pasture at all
times there should be 1.5 acres per horse to allow enough grazing space. Shelter in the
form of a man made building or thick shrubs or trees should be available to enable the
horse to get out of the wind and rain. The horse is able to withstand quite cold
temperatures as long as it is not wet and can get out of the wind. Wooden rails or 5 ft
high livestock netting should be used for the fence. Barbed wire and large square page
wire should not be used because the horse can become tangled and cut themselves.
Horses on pasture are not always easy to catch and if they are being used regularly they
should be kept in a small paddock or in stalls.
Small paddocks are used to house individuals or small groups of horses outdoors.
If housing a group of horses together it is best to keep the group together and not be
continually adding new horses. Once a group has determined its social hierarchy
introducing new horses may cause physical and behavioral conflicts. The pen should be
made of untreated wood or metal rods. The metal rods are best as the horse can not chew
the rods like the wooden boards that eventually have to be replaced. The pen should be
large enough to give each horse 13-15 square meters of space. Feeding can be ad lib or
restricted as long as there is enough feeder space for all the horses. A clean supply of
water should always be available as well as a shelter from the wind and rain.
A lot of horse owners and most research facilities will house horses individually
in stalls for the majority of the time. Box stalls are most often used to house horses
indoors and are made from wood or brick. The stall should be large enough for the horse
to lie down and turn around the minimum size for a full-grown horse is 5 square meters.
A non-slip floor made of either concrete or rubber is essential. The floor is then covered
with bedding of some sort usually straw or wood shavings. A horse-proof bolt or lock on
the door should be installed to prevent escape. Most box stalls are solid from the ground
to about 2m and then bars or metal mesh go to the roof. The bars still allow visual and
olfactory contact between animals. Tie-rings and built in feeders and water bowls are all
handy additions that make the horses time in the stall more comfortable. Although a
horse can move about in a box stall daily exercise is important for the general welfare of
the horse. Horses are often turned out into small paddocks during the day and kept in
their stall at night. The horse can then get exercise and have contact with other horses
which all make for a happy and healthy animal.
Nutrition
When a horse is out on suitable pasture with a good source of water the horse is
able to consume enough nutrients to suit its needs. A horse will consume 25-55 L of
water daily. They like to take water 6-8 times a day so water should always be present
not just offered twice a day. Few horses on pasture become overweight and most
maintain good body condition. The only thing that may need to be added to the horses
diet is a salt lick and possibly a mineral block so the horse can maintain the proper
mineral and microelements in its diet.
In the stable or paddocks horses are usually maintained on good quality hay and
some grain or concentrate ration. Some horses living in paddocks can be fed ad lib hay
as long as they have a large area for exercise and there is enough feeder space for all the
horses. The nutritional needs of a horse are higher in young growing horses and
pregnant mares. The amount of riding or work that a horse is doing will also affect the
amount of feed that is required for the horse to maintain good body condition.
Horses more than any other farm animal seems to have problems with poor
quality hay and other metabolism related conditions. Dusty or moldy hay that may be
suitable for sheep or cattle should never be fed to horses. There is no end of respiratory
and reproductive problems if a horse consumes moldy or improperly cured hay some of
these will be discussed in the disease section.
Identification
Horses can often be identified by their unique coloring or color patterns. When
identifying horses in the lab setting numbered collars or microchips may be used. Many
horse owners are more concerned with people stealing their animals and prefer freeze
branding the horse. A licensed company will mark the horse with a specific code that
identifies the individual horse. The brand can not be tampered with and is registered with
the company that will keep track of the horse as it changes hands. Some people are
concerned that lip tattoos, color patterns and microchips can be altered by horse thieves
and do not provide protection against theft.
Handling and Sexing
Most horses have been trained from a very early age and will be used to being
handled and haltered. The horse should be approached in a firm and confidant manner
from the shoulder area, talking to the horse in a calm voice will announce your presence
to the horse. The most important step to control a horse is to gain control of the head
either with a bridle or with a halter and lead shank. Once the horse is haltered most small
manipulations (blood sampling, injections) and health checks can be preformed. The use
of a twitch on the upper lip of the horse may be used for short times if additional restraint
is necessary. If the horse does not want to stand still for these procedures the front
forelimb can be lifted and flexed to bring the heel against the posterior side of the elbow.
With the limb immobilized the horse can not move about and can not kick. Use of a
blindfold may also help to calm a nervous horse.
If a horse is really difficult to work with it should be taken to a set of stocks.
Stocks should have solid sides and look like a small chute with a door at either end, they
should be narrow enough to prevent the horse from being able to turn around. The horse
is walked into the stocks and then both doors are closed preventing the horse from
moving around. The floor area should be made of a non-slip substance so the horse does
not fall while in the stocks. Rectal exams, tracheal washes and examination of the feet
are done much easier when the horse is restrained in such a manner. In severe cases
drugs may be used to calm a horse or even to get the horse to lie down.
Stallions are usually quite easy to identify because of their behavior and because
of their much larger body size. Stallions in the presence of females tend to move around
with jerky movements and will often rear up. Physically the male will have a fairly
obvious scrotum and the penis is only extended when sexually excited or passing urine.
The female will often have an obvious udder and if the tail is lifted the vulva can be
observed.
DISEASES OF HORSES
Zoonotic Diseases:
As well as Salmonellosis and Rabies the following are zoonitic diseases to be aware of.
The viral disease found in horses that is getting the most attention at the moment
is the West Nile Virus. This mosquito borne disease will rarely cause any clinical signs
in horses and is only detected through antibody blood tests. The few horses that do show
clinical signs would include listlessness, head pressing, loss of coordination and partial
paralysis. There is a vaccine that will protect the horse but information is still emerging
on its effectiveness. The main concern with West Nile is that the disease can be passed
on to humans when they are bitten by an infected mosquito. Birds such as crows and
magpies seem to be the main reservoir for this virus. Most people that become infected
never know that they have the disease as the body fights off the virus. A few people may
show mild flu-like symptoms including fever, headaches and body aches. People with
weak immune systems may exhibit more severe signs such as meningitis and encephalitis
that in very rare cases can be fatal. Long-term effects of this disease are yet to be seen.
Western Equine Encephalitis (WEE) and Eastern Equine Encephalitis (EEE)
are similar to the West Nile disease and are again caused by infected mosquitoes. The
virus affects the central nervous system causing brain damage, paralysis, blindness or
even death. Vaccines are available to prevent the disease but there is no treatment once
an animal is infected. WEE is also a zoonotic disease meaning that people can become
infected if they are bitten by a disease carrying mosquito. Most infected people will
experience a fever, headache and drowsiness, very rarely it can lead to death. The best
prevention is to avoid areas where mosquitoes live, wear insect repellant and wear long
sleeved clothing.
There are presently vaccines available for Rabies, West Nile Virus, and Eastern
and Western Equine Encephalitis.
USES IN THE LAB
Horses are very expensive animals to buy and maintain in a research setting and
are therefore used mainly to investigate specific problems of horses. Pharmacology
studies to investigate how anesthetics, tranquilizers and analgesics affect horses as well
as nutritional studies affecting brood mares, foals and competitive horses are the main
areas of equine research. Colic, that accounts for 40 % of all equine deaths is an area that
still gains attention as does lameness which is the main reason horses require the
assistance of a veterinarian. Horses due to their large size can donate large quantities of
blood that can be used as media for microbiology tests. PMU farms produce pregnant
mare urine that is used in the pharmaceutical industry to produce products that contain
estrogen. PMU farms are becoming less prevalent now due to synthetic estrogen
production.