Animal breeding
Animal breeding is the deliberate practice of selecting and mating domesticated animals to enhance their utility for human purposes. This practice has been in place since the domestication of animals and traditionally relies on the selection of individuals with desirable traits to produce improved offspring. Advances in technology, especially since the mid-20th century, have enabled more precise identification of superior animals and facilitated their use in breeding programs through methods like artificial insemination. Genetic inheritance plays a crucial role in breeding, as the traits of animals are governed by their genetic makeup, which is influenced by alleles inherited from their parents.
The selection and mating systems used in animal breeding can vary, with strategies such as complementarity and crossbreeding employed to enhance genetic diversity and productivity. Moreover, environmental factors, including climate and nutrition, significantly influence an animal's performance, highlighting the need to consider both genetic and environmental interactions in breeding decisions. Looking ahead, molecular biology and biotechnology promise to revolutionize animal breeding by enabling the identification and transfer of advantageous genes, ultimately aiming to improve animal species in ways that better serve human needs.
Animal breeding
Animal breeding is the practice of selecting and mating domesticated animals to enhance their contributions to humans.
Background
Animal breeding has been used to produce animals more useful to humankind since animals were first domesticated. Traditionally it involved selecting individual animals for desired traits and mating them, with the intent of producing improved offspring. In the second half of the twentieth century, extensive performance records and computer-aided analysis permitted superior animals to be identified more accurately and, via reproductive technologies, to be utilized more rapidly for improving the major livestock species. In the future, molecular biology and promise to expedite this process by identifying desirable genes from the same or different species and incorporating them into domesticated animals. Animal breeding will continue to augment the value of domesticated animals as a renewable resource.
Genetic Inheritance and Determinance
Animal breeding is predicated on two principles: that the genes of an animal are inherited from its parents and that its genes are an important determinant of its appearance, structure, behavior, and productivity. In animal species, almost all genes are located in the nucleus of an organism’s cells; these nuclear genes are inherited from both parents. A few genes, located outside the nucleus in subcellular structures called mitochondria, are derived only from the mother. The full complement of genes, known as the genome, directs the development of an individual animal, the synthesis of all body tissues, including metabolic machinery, and to a large extent the characteristics or traits exhibited. Different forms of genes, referred to as alleles, are responsible for the individuality of living things.
Some characteristics are determined by alleles of one gene—for instance, the absence of horns or the occurrence of a metabolic disease. In such cases, a single mutation can lead to a deleterious condition. However, most traits of significance involve alleles of more than one gene. Superior characteristics for growth rate or milk yield, so-called polygenic traits, result from the combination of alleles of many genes. Animal breeding seeks to improve genetically the future population of a particular species by increasing the proportion of desirable alleles or the appropriate combination of such alleles. Genetic improvement requires selection of appropriate breeding animals and a mating plan for such animals.
Selection and Mating Systems
Selection is the process of determining which animals are to be used as breeding stock. The simplest form of selection considers only traits of the individual, whereas more complex selection takes account of additional information on relatives, such as siblings, parents, and offspring. The accuracy of predicting genetic progress is improved by considering relatives. This process requires reliable measures for desired traits, acquisition of records from numerous animals, and analysis of the records, which has been aided by advances in statistical theory and computational power. The result is a ranking of animals based on their genetic merit for single or multiple traits.
Several systems have been used for mating selected animals. One involves complementarity, whereby individuals with high genetic merit for different traits are mated. It has been used to improve livestock in developing countries by mating animals adapted to local conditions with highly productive ones from developed countries. The beef cattle, swine, and poultry industries make heavy use of crossbreeding, in which animals from different breeds are mated. One of its advantages is the “hybrid vigor” that results. Another system is mating the best to the best. One of its hazards is inbreeding, or the mating of relatives, which often results in decreased fertility and viability.
Environmental Factors
Performance or productivity is determined not only by genetics but also by environmental factors. Climate, nutrition, and management can affect the extent to which the genetic potential of an animal is realized. Because the productivity of an animal can be affected deleteriously by heat and disease, and other environmental factors can influence animals’ performance. Similarly, the management system used, whether intensive or extensive, can also affect productivity. Accordingly, the most productive animal under one set of conditions may not necessarily be the most productive under another. Interactions between genetics and the environment must be considered in animal breeding.
Post-1940s Developments
Beginning in the mid-twentieth century, reproductive technologies, most notably artificial insemination, contributed to rapid improvement in animal performance. These technologies permit animals with the best genetics to be used widely, resulting in numerous offspring from which to select the best breeding stock for the next generation. As a result of intensive selection and management in the United States beginning in the 1940s, milk production per cow has more than tripled. The growth rate of chickens has more than doubled, as has egg production. Such increases have occurred concurrently with a higher efficiency in raising animals for human food.
Molecular biology and biotechnology hold the potential to alter animal breeding processes significantly in the early twenty-first century. Further understanding of the genomes of livestock species should permit identification of specific genes that will increase the productivity of these animals. One approach, known as marker-assisted selection, would use genetic markers associated with desirable production characteristics to enhance genetic improvement. If such markers prove to be accurate predictors, they will allow the selection of desirable animals long before performance records are available. Transfer of desirable genes, within or between species, may also expedite the generation of superior animals. The goal of animal breeding can be expected to remain similar to that of the past—namely the improvement of animal species to better meet human needs—but the precise nature of the improvements desired and the methodologies used to achieve them could be vastly different.
Bibliography
"Animal Production." US Department of Agriculture, 2024, www.usda.gov/farming-and-ranching/animal-science/animal-production. Accessed 26 Dec. 2024.
Bourdon, Richard M. Understanding Animal Breeding. 2d ed. Upper Saddle River, N.J.: Prentice Hall, 2000.
Falconer, D. S., and Trudy F. C. Mackay. Introduction to Quantitative Genetics. 4th ed. New York: Longman, 1996.
Field, Thomas G., and Robert E. Taylor. Scientific Farm Animal Production: An Introduction to Animal Science. 9th ed. Upper Saddle River, N.J.: Prentice Hall, 2008.
Sandøe, Peter, and Stine B. Christiansen. Ethics of Animal Use. Oxford, England: Blackwell, 2008.
Schatten, Heide, and Gheorghe M. Constantinescu, eds. Comparative Reproductive Biology. Ames, Iowa: Blackwell, 2007.
Van der Werf, Julius, Hans-Ulrich Graser, Richard Frankham, and Cedric Gondro, eds. Adaptation and Fitness in Animal Populations: Evolutionary and Breeding Perspectives on Genetic Resource Management. London: Springer, 2009.
Weaver, Robert F., and Philip W. Hedrick. Genetics. 3d ed. Dubuque, Iowa: W. C. Brown, 1997.
Wellman, Robin. "Defining Valid Breeding Goals for Animal Breeds." Genetics Selection Evolution, vol. 55, no. 80, 21 Nov. 2023, doi.org/10.1186/s12711-023-00855-6. Accessed 25 Dec. 2024.