Animal breeding and husbandry
Fields of study: Animal science; genetics; statistics; genomics; biotechnology; animal nutrition
Summary: Animal husbandry is the agriculture practice of the production and care of animals. Animal husbandry is now usually called animal science in universities, since academic studies involve research and the application of scientific principles. Animal breeding is often considered part of husbandry and is the application of genetic principles in the development of breeds and lines of animals for human purposes. Animal breeding principles are also used in captive breeding programs in order to propagate endangered wildlife species. The development of a leaner line of pigs and a strain of chickens that produces more eggs are examples of animal breeding.
Key Terms and Concepts
biotechnology: The application of biological techniques to practical applications.
breed: A population of animals within a species that have similar identifying characteristics.
complimentarity: The improvement in performance of offspring from parents with different but complimentary breeding values.
correlated characters: Traits that change together, either in the same or opposite directions.
outbreeding: Mating of unrelated animals, such as between different breeds or lines.
genotype: The genetic makeup of an animal.
heritability: A measure of the relationship between phenotype and breeding value.
hybrid: The offspring of breeding different species, lines, or breeds.
inbreeding: Mating of closely related animals.
line: A group of related individuals within a breed.
mating system: A set of rules for mating selected males with selected females.
phenotype: The observed physical appearance or performance of a trait.
polygenic trait: A trait affected by many genes, with no gene having a dominating influence.
population: A group of intermating individuals within a herd, breed, or species.
trait: Any observable or measurable characteristic of an animal.
Definition and Basic Principles
Animal husbandry is concerned with all aspects of the management, care, and breeding of farm animals. The goal of animal husbandry is to provide the best conditions (given economic constraints) to maximize productivity in terms of body weight, wool, milk or eggs. The animals must remain in good health in order to attain this productivity and to reproduce. Animal husbandry involves the choice of proper feeds, housing, and suitable animals.
Animal breeding begins with a measurement of desirable traits (phenotype) that relate to improved animal production. The breeding value of an animal, however, is the degree to which its underlying genotype can be transmitted to its offspring. Current methods of breeder selection combine traditional measurements of quantitative traits with the new technology of genome analysis, which aid in determining the breeder’s genotype. The rate of genetic change (in animal populations) is directly related to accuracy of selection, selection intensity, and genetic variation in the population; and is inversely related to generation interval. There are two primary types of breeding programs: development of breeds or lines that can be used as breeders (seedstock), and development of crossbreeds for production. Crossbreeds demonstrate improved productivity due to hybrid vigor and complimentary traits exhibited by their parents.
@SUB = Background and History. Animal husbandry began with the domestication of animals for human purposes from around 10,000 – 5,000 BC. Sheep were the first to be domesticated, followed by cattle, horses, pigs, goats, and finally chickens and turkeys. A relatively small number of species have been domesticated, since they must possess several suitable characteristics that allow them to adapt to interaction with humans. Their diet must be simple to provide as the early domesticated animals depended on grazing and foraging for their food. They must be able to breed in captivity, and grow and reproduce at a relatively short time interval. They must have a calm, predictable behavior and a cooperative type of social structure.
The beginnings of animal breeding began by the time of the Roman Empire or earlier. Early breeders recognized desirable traits in animals that they wanted to propagate, so they selected those animals for mating. The characteristics of domesticated animals began to vary greatly from their wild cousins and became totally dependent on their human captors. Systematic selective breeding methods began with the English sheep farmer, Robert Bakewell. Bakewell sought to increase the growth rate of sheep so that they could be slaughtered at an earlier age, to increase the proportion of muscle, and to improve feed efficiency. The application of genetics in animal breeding began in the twentieth century. Jay Lush, a professor at Iowa State, is considered a pioneer in the application of genetic techniques in animal breeding.
How It Works.
Husbandry. Farm animal production is an economic venture; undertaken to produce food (meat, milk and eggs) or other animal products, such as wool, hides, hair, and pelts. Through the process of animal husbandry, growers seek to create conditions that maximize production of animal products at the lowest cost. With advancing technology and improvements in breeds, animal production has evolved from extensive systems to increasingly intensive systems. Intensive systems put more demands on good husbandry practices, since the animals are often under more stress and are more dependent on humans for their well being. Extensive systems involve keeping animals on pastures or in small pens with minimal housing. Intensive systems are most advanced in the case of poultry. Broilers (meat animals) are kept in total confinement indoors, while laying hens are kept completely in cages. Swine are also commonly kept in confinement, usually on slat or grid floors made of metal. Confinement operations require closer attention to the requirements of ventilation, sanitation, and animal interactions. Beef cattle are still grown on range or pasture, but now it is more common to finish them in large feedlots concentrating thousands of animals. Dairy cattle usually have pastures for grazing, but are practically always milked by machine in parlors. Sheep are still largely grazed on range or pasture for most of the growing cycle.
Traits and Breeding Value. The selection of animals in the early days of animal breeding was dependent upon physical or quantitative traits exhibited by the animal with no understanding of the underlying genetic principles. These observed or measured traits are known as the phenotype of the animal. The animal’s phenotype is a result of the interaction of its genotype (genetic makeup) with the environment. The goal of animal breeding is to produce animals in a herd, flock, line, strain or breed that possess superior phenotypes that can be passed on to future generations. The degree to which observed phenotypes can be transmitted to offspring is known as heritability, and is a measure of the breeding value of the animal. The selection of desired traits depends on the species of animal and the intended purposes for raising them. The selection also depends on the management practices adopted by the farmer, and the relationships between farm inputs and the value of the animals. Examples of traits include calving interval for beef cattle, milk yield for dairy cattle, litter size for swine, first year egg numbers for hens, and breast weight for meat chickens. The performance of traits can depend on the environment. A high producing Holstein cow may not produce as well in the tropics since she is not heat tolerant.
Rate of Genetic Change. Progress in a breeding program is related to the rate of genetic change in a population. There are several factors that affect this rate of change: accuracy of selection, selection intensity, genetic variation, and generation interval. The accuracy of selection relates true breeding values to their prediction for a trait under selection. Selection intensity refers to the proportion of individuals in a population that are selected. Populations selected more intensely will be genetically better than the average, leading to a faster rate of genetic change. Populations exhibiting greater genetic variation among individuals have the potential for more rapid genetic change. Finally, species having a short generation interval will have a faster rate of genetic change.
Multiple Trait Selection. Breeders seldom select just one trait for improvement, since a combination of traits is important for economic success of the enterprise. In fact, selection for one trait usually affects the response to traits not selected for due to the phenomenon of correlated response. The major cause of correlated response is pleiotrophy, the situation where one gene influences more than one trait.
Breeders practice multiple trait selection by three primary means. Tandem selection involves selecting for one trait, then another. Independent culling levels sets minimum standards for traits undergoing selection, and animals are rejected that do not meet all the standards. Finally, the method of economic selection indexes assigns weighted values for the various traits.
Applications and Products
Seedstock. A term commonly applied to breeding stock is seedstock. The purpose of breeding stock is to provide genes to the next generation, rather than to be producers of meat, milk, wool, or eggs. Traditionally, seedstock have been purebreds, but more recently there have been increasing numbers of nonpurebred stock. Seedstock animals are obtained by programs of inbreeding. These programs result in an increase in homozygous or similar genotypes. As a result, seedstock have a greater tendency to pass on performance characteristics to their offspring, an ability known as prepotency. One risk of inbreeding is the expression of deleterious genes resulting in reduced performance, known as inbreeding depression. Outcrossing or linecrossing is a milder form of inbreeding, and involves mating animals from different lines or strains within the same breed. This process still maintains a degree of relationship to highly regarded ancestors, but is less intense than breeding first degree relatives. Outcrossing allows for the return of vigor that can be lost by inbreeding, while still maintaining the genetic gains obtained by inbreeding.
Crossbred animals. Mating animals from different species is known as crossbreeding. The resultant offspring are known as hybrids. Today, even hybrids are commonly used in crossbreeding systems. Crossbred animals are used for production and are designed to take advantage of hybrid vigor and breed complementarity. Hybrid vigor is the increased performance of offspring over either purebred parent, especially in traits such as fertility and survivability. A classic example of complementarity is the crossing of specialized male and female lines of broiler chickens. Individuals from male line are heavily muscled and fast growing but not great egg producers, while individuals from the female line are outstanding egg producers.
Artificial insemination (A.I.) is a reproductive technology that has been used for a long time. Semen is collected from males and is used to breed females. Since semen can be frozen, it can be used to eventually sire thousands of offspring. This expanded use of superior males can markedly increase the rate of genetic change. Estrus synchronization facilitates artificial insemination by assuring that a group of females come into estrus at the same time.
Embryo transfer involves collecting embryos from donor females and transferring to recipient females. Although the motive for embryo transfer is to propagate valuable genes from females, the number of progeny is much less, and the procedure is more difficult and costly than A.I.
In vitro fertilization. A variation of embryo transfer is the emerging technology of in vitro fertilization. This technology involves collecting eggs from donor females, which are then matured, fertilized, and cultured in the laboratory. The embryos can then be transferred to recipient females or frozen for later use. Currently, the procedure is very expensive and time consuming. However, it has the potential to aid genetic selection and crossbreeding programs. The genotype of the embryo could be determined before pregnancy. Knowing the genotype could be particularly important for dairy cattle which frequently have fertility problems.
Cloning is the production of genetically identical animals. Cloning allows the breeder to predict the characteristics of offspring, to increase uniformity of breeding stock, and to preserve and extend superior genetics. The preferred method of cloning, somatic cell nuclear transfer, involves removing the nuclei from multiple unfertilized eggs, followed by transfer of somatic cells from the animal to be cloned. If the process is successful, the resulting embryo is placed in the uterus of a surrogate mother for development.
Genetic marker technology was made possible with the development of reasonably inexpensive and efficient genomic analysis of farm animals. The term commonly used in the genetic marker field is quantitative trait loci (QTI). Animal breeders select for traits of economic importance which are largely quantitative traits. These traits usually controlled by a large number of genes, even into the thousands. Each gene can contribute a small portion to the total genetic variation of the trait. Since the location (locus) and identity of these genes on the DNA molecule is frequently unknown, the use of genetic markers has become important. Genetic markers are associated with quantitative genes and can be identified in the laboratory.
Another term associated with genetic markers is single nucleotide polymorphisms, or SNPs. Nucleotides are the building blocks of DNA, and polymorphism means “many forms.” Nucleotides are made of one of four different bases. Genes are made of many nucleotides. The exchange of one base for another in a nucleotide is a SNP, which can change the expression of a gene. Instead of analyzing the entire genome of an animal, the dense SNP array test measures around 50,000 SNPs, which is then related to the genetic merit of the animal. With traditional breeding programs, each offspring is assumed to have inherited an average sample of genes from his or her sire (father) and dam (mother). Full siblings have equal “parent average” or PA but are expected to share only half of their genes as copies of the same genes in their parents. Considerable improvements in breeding value have been demonstrated by the use of a “g PTA” calculation which combines genomic data with the traditional parent average data.
Impact on Industry
In 1966, the World Congress on Genetics Applied to Livestock Production was established to provide an avenue for researchers to present findings of their research. The areas of research reflect the concerns or problems of the respective countries. Most of the world papers presented at the Congress every four years have been on breeding for meat or milk production, estimating genetic parameters, and designing sustainable breeding programs. In spite of widespread dissemination of research findings worldwide, there is a large gap in biotechnology applications between developing and developed countries. Research partnerships between developed and developing countries are much fewer than between developed countries. The only exception is artificial insemination which is not really a new technology. The more complex technologies such as embryo transfer and genetic markers are adopted less frequently.
Government and University Research. Animal breeding research at the federal level takes place within the Agricultural Research Service (ARS), a branch of the U.S. Department of Agriculture. Research takes place at 100 stations located throughout the country as well as in some foreign countries. The ARS welcomes collaboration with businesses, state and local governments, and universities. Many of its accomplishments are a result of these joint efforts. ARS researchers adopted quantitative measures for evaluating breeding stock early on, leading to calculations that predict the average performance of offspring, such as “Expected Progeny Difference” for beef cattle, or “Predicted Transmitting Ability” for dairy cattle. ARS researchers have been deeply involved in genome sequencing of farm animals. By the use of the Illumina Bovine SNP 50 Bead Chip, the genotypes of more than 40,000 animals have been determined. In 2007, The USDA Animal Genomics Strategic Planning Task Force, comprising members of the ARS, the Cooperative Research, Education, and Extension Service, and university collaborators, developed the “Blueprint for USDA Efforts in Agricultural Animal Genomics.” The blueprint identifies three major areas of focus: outreach, discovery, and infrastructure.
The land grant college system inaugurated a close relationship between the federal government and the states. The Morrill and Hatch Acts provided federal funds for the establishment of state colleges of agriculture and for associated agricultural research stations. In order to disseminate research information to producers and consumers of agricultural products, the Cooperative Extension Service was also established. Practically all animal science departments have faculty that have had assignments in foreign countries with the largest number being in Latin America.
Industry Research and Applications. The new technology of SNP markers is revolutionizing the selection of animal breeders. This technology was developed in a partnership among the companies Illumina, Inc. and Merial, the USDA Agricultural Research Service, the National Association of Animal Breeders, and researchers at several universities and institutes. The researchers found that the breeding value of an animal could be determined by association of these genetic markers with production traits. The genetic evaluation of breeding stock has two advantages over the traditional parent average method, speed and lower cost. Instead of waiting for proof of breeding value through progeny performance, the animals can be selected very early in their lifetime. Selection by genetic markers is particularly useful for identifying males with low heritability traits such as fertility and longevity.
The nature of animal breeding companies is changing, and many do not maintain their own breeding stock. They also provide services such as semen collection or embryo transfer, and maintain and sell the semen and embryos. The private sector is playing an increasingly important role in livestock genetic improvement. Specialized breeding firms now supply virtually all commercial poultry breeding stock as well as increasing amounts of genetic material for swine, beef, and dairy cattle. Private investment in livestock breeding is affected by demand from producers, market structure, intellectual property protection, new technologies, and market globalization.
Careers and Coursework
The field of animal husbandry is now called animal science in colleges and universities in order to reflect scientific study and applications in the field. Students specifically interested in animal husbandry should concentrate on coursework and experience related to production and management. Animal science also encompasses areas such as agribusiness, Agricultural Extension Service, and research and teaching. Job titles in animal husbandry can include livestock or dairy herdsperson, stable manager, veterinary technician, feed mill supervisor, or farm manager. Previously, on-farm experience was adequate to work in animal husbandry, but it is now a more complex field. A two year Associates degree should be considered minimal for the field, while a four-year bachelor’s degree would be beneficial for managerial positions. Course work can include animal production, biology, chemistry, animal growth and development, physiology, animal nutrition, biotechnology, farm management, and economics.
A career in animal breeding and genetics requires a PhD degree, whether employment is in academia or industry. The careers can include such specialties as quantitative or molecular genetics, bioinformatics, immunogenetics, and functional genomics. The prerequisites for graduate studies typically include undergraduate course work in animal science. Graduate courses can include animal breeding, statistics, endocrinology, genome analysis, population and quantitative genetics, animal breeding strategies, statistical methods, and physiology and metabolism. Specific course work varies depending on the school.
@SUB = Social Context and Future Prospects
There has recently been some controversy about the increased alliances and funding of state agricultural experiment stations (SAES) with private firms. Since SAES are public institutions, some people feel that they may be compromising their independence and objectivity. However, SAES is more involved in basic research, while private firms follow-up by conducting the necessary practical research leading to commercialization of new products.
The modern “factory farming” methods, with poultry, swine, and other farm animals kept in confinement and in crowded conditions has been condemned by animal rights activists. They claim that since the animals are often not able to perform their natural and instinctive behaviors they are suffering. Animal science departments have been aware of these criticisms, and have developed a new field of farm animal welfare. Faculty positions in the emerging field have been filled, and students are being introduced to the concepts. Animal welfare is now studied academically in a manner that is validated, measured objectively, and is reliable. The discipline considers the relationship of farm animal welfare to their environment in three areas: how the animal feels, their fitness and health, and their natural behaviors.
Genome analysis has come of age in farm animal breeding. Instead of selecting animals by appearance and waiting for proof of breeding value by performance of offspring, genome analysis can allow selection of valuable breeders soon after birth.
Criticism of “factory farms” by animal welfare activists is prompting animal science departments to add animal welfare specialists to their staff.
Improved animal husbandry, feeding, and breeding has led to extraordinary improvements in animal productivity. Since 1950, milk production per cow has risen from 5,313 lbs to 16, 400 lbs; age to market weight of broiler chickens has decreased from 12 wks to 7.3 wks; eggs per hen per year has risen from 174 to 254 eggs.
Captive breeding has resulted in saving many wild animal species from extinction. These species include bison, wolves, Peregrine Falcon, California Condor, and Whooping Cranes.
Genomic Estimated Breeding Values are expected to revolutionize dairy breeding programs. The calculation combines traditional parent average evaluation programs with the new genetic marker discoveries.
Most poultry and swine grown for meat are crossbred, while purebred stock are used as breeders.
New technologies of embryo transfer, cloning, and genetic markers promise to revolutionize animal breeding.
Bourdon, Richard. Understanding Animal Breeding. 2nd Edition. Upper Saddle River, NJ: Prentice Hall, 2000.An excellent basic text on animal breeding that presents concepts with a minimum of mathematics.
Cassel, Bennet. “Genetic Marker Technology and its Impact on the Dairy Industry.” Southern Dairy Conference Proceedings June 2009
http://www.extension.org/pages/Genetic_marker_technology_and_its_impact_on_ the_dairy_industry. Accessed August 2010. An excellent basic discussion on SNP array terchnology and its use with parent average data to improve breeding programs.
Dekkers, Jack. “New Technologies in Animal Breeding.” National Swine Improvement Federation Proceedings. Volume 24, November 16-17, 1999.
Provides an excellent background on the field of molecular genetics and how it can be applied to current breeding programs.
Green, R. “ASAS Centennial Paper: Future needs in animal breeding and genetics.” Journal of Animal Science. 87 (2009): 793-800. Addresses the challenges in implementing the merging of quantitative and genomic approaches to animal breeding.
Johnson, A. “ASAS Centennial Paper: Farm animal welfare science in the United States.” Journal of Animal Science. 87 (2009): 2175-2179. Describes the newly emerging field of animal welfare science, how the field is taught and researched in universities, and its relationship to societal issues.
Taylor, Robert and Thomas Field. Scientific Farm Animal Production. Upper Saddle River, NJ: Prentice Hall, 2007. Provides an excellent introduction to all aspects of animal husbandry and production of all major farm animals,
David Olle, M.S.
Bourdon, Richard. Understanding Animal Breeding. 2nd Edition. Upper Saddle River, NJ: Prentice Hall, 2000.
Taylor, Robert and Thomas Field. Scientific Farm Animal Production. Upper Saddle River, NJ: Prentice Hall, 2007.
Cassel, Bennet. “Genetic Marker Technology and its Impact on the Dairy Industry.”
Southern Dairy Conference Proceedings June 2009
Dekkers, Jack. “New Technologies in Animal Breeding.” National Swine Improvement Federation Proceedings. Volume 24, November 16-17, 1999.
Green, R. “ASAS Centennial Paper: Future Needs in animal Breeding and Genetics.”
Journal of Animal Science 87 (2009):793-800.
Johnson, A. “ASAS Centennial Paper: Farm Animal Welfare Science in the United States.” Journal of Animal Science. 87 (2009): 2175-2179.