 |
| iStock.com |
Sheep are commonly used in
biomedical research and education. |
Sheep Senses
Reproduction
Behavior & Diet
Domestication
Sheep and Humans
Sheep in Medical Research
Cloning and Genetic Engineering
Sheep in Education
Life in the Laboratory
There are 200 breeds of domestic sheep (Ovis aries) that vary greatly. They range in color from creamy white to dark brown and black. Male sheep or rams weigh 150 pounds to 450 pounds while female weigh between 100 pounds and 300 pounds. Long-haired sheep have coats that must be sheared at least once a year. Short-haired breeds lack wool or naturally shed their coats. Both types of sheep are used in agricultural and medical research.
Sheep Senses
Many of the sheep's senses are well developed in order to help them avoid predators. Sheep are able to spot other animals from up to 1,500 yards away and have excellent peripheral vision. Sheep also have excellent hearing and a sense of smell. Sheep use their sense of smell to find water and their lambs or flock members, and rams use it to detect females in estrus.
|
Facts About Sheep |
|
 The age of a sheep is determined by their teeth. Sheep develop two permanent teeth per year until they have eight. A 2-year-old sheep is called a two-tooth, etc.
Sheep can recognize flock mates even after years of separation.
Sheep have a near 270-degree radius of view allowing them to see nearly behind their back.
Sheep make distinctive sounds or ‘bleats’ that indicate hunger, fear, sickness, etc. which can be recognized by other flock members as well as the sheep’s human caretakers. |
Reproduction
Ewes usually give birth to twins, sometimes triplets, and primarily do this during the spring. Gestation lasts about 150 days. Because of their playful nature and innocence, lambs are often used to symbolize springtime and new beginnings. Lambs reach sexual maturity at about 1 year old. The sheep life span is 8 years to 14 years, although some live to be 20 years old.
Behavior & Diet
Sheep exhibit a very strong flocking behavior and establish well-defined social relationships with other members based on age and sex. Sheep must have the company of their flock in order to maintain their well-being and protect against predators. Despite their many admirable traits, the sheep's instinctive flocking behavior is commonly interpreted as a lack of intelligence. In reality, sheep demonstrate surprising memory and problem-solving skills.
Sheep on the Yorkshire moors are known as the only farm animal to learn how to pass through metal cattle grids, which are installed to keep hoofed animals from passing over roads. A study conducted at the Babraham Institute in Cambridge, England showed that sheep can remember the faces of 50 other sheep for up to two years. Australian researchers found that sheep can learn to navigate a complex maze, improve their performance and retain information for up to six weeks.
Sheep spend most of their day grazing and ruminating their food. Sheep ruminate, or re-chew ingested food, while they rest. The sheep stomach is large and complex with four chambers that enable sheep to get the most nutrients from their food. Sheep typically eat grass, weeds and shrubs on the range and supplement their diets with a wide variety of grain and hay on farms. Drinking water for sheep must be clean and free flowing because sheep will not drink standing or contaminated water.
Domestication of Sheep
Sheep were first domesticated in the Middle East and Central Asia about 10,000 years ago. Domestic sheep were introduced to the southwestern United States in 1519 by Spanish troops under Hernando Cortés during his exploration of Mexico. American colonists quickly created a successful market for wool by shipping it to other countries in exchange for goods. In 1698, England outlawed the wool trade in America. Eventually, the Wool Act along with the Stamp Act led to the American Revolutionary War.
|
Sheep |
Terms |
| Sheep
| Usually refers to females over one year of age who have given birth |
| Ewe |
Mature female sheep |
| Ram |
Mature male sheep |
| Lamb |
Newborn sheep |
| Wether |
Neutered male sheep |
Sheep and Humans
Because of their importance to humans for thousands of years, sheep are prominent figures in folklore, cultures and, particularly, religions throughout the world. Metaphorically, the term Shepherd is used for God, especially in the Judeo-Christian tradition. The Old Testament heroes Abraham, Jacob, Moses and King David all worked as shepherds. In Christianity, shepherds and their flocks are believed to be the first witnesses to the nativity of Christ.
In addition, Jesus is referred to as the Good Shepherd and the Lamb of God. Religious traditions also involve the sacrifice of sheep as in the Muslim celebration of Eid ul-Adha (festival of sacrifice) or a meal of lamb as in Greek Easter celebrations. In ancient Egyptian religion, the ram, or Aries, symbolized the head of Amun, considered to be the leading deity whom all other gods followed. The Ram or Aries is also the first sign in the western zodiac symbolizing an animal of great courage.
Sheep in Medical Research
Medical research on sheep began in 1667 when French physician Dr. Jean-Baptiste Denis conducted a blood transfusion from a sheep to a man. The failure of this experiment led to further research on blood compatibility and transfusion techniques. Sheep were also used in developing a vaccine for anthrax, and studies on the pathogenesis of tuberculosis.
In more recent years, research on sheep led to the development and testing of treatments for infant respiratory distress and the development of the arteriovenous shunt and surgical techniques that are used during kidney dialysis.
Sheep are commonly used to research human pregnancy because of their short gestation periods, and similar newborn lambs' and human infants' weights. They are also used in research into joint reconstruction, aneurysms and organ transplantation. Because of the sheep’s four-chambered stomach, they have been used to study ruminant nutrition and animal production. The most well-known use of sheep in research is their part in the study of genetic engineering and cloning research.
Dolly, the famous cloned sheep, was the first mammal cloned from an adult cell. Dolly was born in July 1996 at the Roslin Institute in Scotland. She lived for six years, but her life was fraught with serious health problems, including lung disease and severe arthritis. Her poor health was attributed to premature aging in cloned animals.
 |
| ©The HSUS |
Cloning or genetic engineering research
presents major animal welfare concerns |
Cloning and Genetic Engineering
Even cloning researchers admit that genetic engineering research presents major animal welfare concerns. The federal Animal Welfare Act does not cover farm animals used in cloning, genetic engineering or any agricultural research. The lack of oversight results in gross neglect. In 2004, 38 pregnant sheep died at the University of Nevada Agricultural College after they were abandoned for four days without food or water.
One large-scale study of cloned sheep found that out of 93 attempts, none survived beyond four weeks. Most died in in utero and the rest succumbed to severe health complications. Dolly was the only successful birth out of an initial 277 attempts involving 13 surrogate mothers. Fetal overgrowth is a major problem with cloned sheep. Birth weights of lambs may be up to 25 percent heavier than normal, which stresses the mother, and usually requires she undergo a cesarean delivery and other invasive procedures that she could endure repeatedly. More on cloning and genetic engineering.
Sheep Used in Education
Live, anesthetized sheep are used to demonstrate trauma skills during trauma training courses in United States medical centers. Many physicians and students object to the use or killing of animals for trauma training and also assert that procedures are better demonstrated using human cadavers or manikins such as the highly advanced TraumaMan® model.
| |
| Data from the USDA 2004 Animal Use Statistics. PDF |
Life in the Laboratory
Sheep used in research are obtained from breeding facilities that sell directly to laboratories or from farmers. Depending on the type of research conducted, the sheep might be used for multiple experiments. They can also be sold for their meat after they are no longer needed for research or they can be euthanized by injection.
Life in a research setting is difficult for sheep because they are fearful by nature and are very apprehensive in new situations. Sheep used in research face new and changing environments, new diets, drastic changes in lighting, isolation from other sheep, exposure to human lab personnel (who are viewed as predators), and many other factors that are extremely stressful. Stable social relationships and adequate time to adjust to new situations are vital to the welfare of research sheep.
