by R.L. Willham
The science of animal breeding is concerned with the application of the principles of population genetics to the improvement of domestic animals. Population genetics deals with the forces that influence the genetic composition of biological populations and owes its existence to developments in evolution and population biology and to the global need for improvements in domestic crops and livestock. Livestock breeders, using selection, adapted their stock to meet this need long before animal breeding became a science. With the rediscovery of Mendel in 1900, Wentworth and other animal husbandmen began to explore the art of the breeder in the light of Mendelian genetics. Concurrently, the basic theory of population genetics was formulated by Fisher and Wright. Never before in the history of biology had theory, based on the algebra of ½, so outstripped experimental evidence in any field. This has tended to make population genetics (and, as a result, animal breeding) unique among the sciences. During this formative period, hybrid maize had its first impact on the scientific community and on agricultural production.
Research, teaching and extension
Lush developed a graduate programme starting in the 1930s that produced students trained to apply the principles of population genetics to the improvement of domestic livestock. The 1940s saw dairy artificial insemination, and Dairy Herd Improvement Association (U.S. Department of Agriculture) records, with their symbiotic effect on sire evaluation, begin the revolution in dairy cattle breeding. The poultry industry quickly developed a few giant poultry breeding companies.
The author is Professor in the Department of Animal Science, Iowa State University, Ames, Iowa 50011, United States. Journal Paper No. J-8289 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 2000.
After the Second World War, several regional projects, patterned after the successful regional swine-breeding laboratory, were started with adequate funding from state experiment stations and the U.S. Department of Agriculture to initiate some large-scale animal breeding research projects. Today the fruits of these long-term investigations are seen in the dairy, poultry, swine, sheep and beef industries. The extent of breeding technology utilized by the various industries is related to their reproductive potential or to a reproductive innovation such as artificial insemination.
Animal breeding research has been conducted mainly in the structure of land-grant universities under the leadership of professors with responsibilities in research, teaching and, to some extent, extension. Research provided the primary base of experience which influenced teaching and extension. Large animal research in the field of breeding was developed through long-term projects in experiment stations. Typically this research approached genetic problems peculiar to a species, such as the amount and kind of genetic variation available, the heritability and repeatability of traits, and the response to inbreeding and crossbreeding. Considerable theoretical studies resulted from a need to explain research findings, as evidenced by the development of concepts relating to maternal effects (Dickerson, 1974).
Animal breeding research tended to develop breeding technology that can be applied by breeders in the various livestock industries. This contrasted with plant breeding research, where the basic germ plasm was developed by the plant breeders themselves. The controversy over these two philosophies of research has been exciting, but the development of breeding principles has prevailed.
Today, research in animal breeding has problems both in large and laboratory animals. Funds for this research are being reduced by inflation and by an emphasis on short-term projects with the highest probable net return to the livestock industry. Also, in the land-grant system excellence in teaching is emphasized, sometimes at the expense of research. Nevertheless, important biological and theoretical questions remain unanswered in animal breeding. Opportunity does exist for research even though the scope of investigations and the basic nature of the projects may be changing. The development of research capabilities by the livestock industry itself and by the U.S. Department of Agriculture in largescale projects, when coupled with university research, can add substantially to knowledge in the field of animal breeding.
Inasmuch as animal breeding is an applied field, it becomes difficult to decide when work is primarily population genetics and when it is animal breeding. The line is somewhat like the difference between applied and fundamental or basic research. To pick up contributions from the field of molecular, classical and physiological genetics and from evolution and population biology is even more difficult. The general facets of current work in animal breeding may be classified into theoretical animal breeding, animal research and application. Each of these facets may in turn be further subdivided.
Theoretical animal breeding
This is defined as the development of a concept, usually with a mathematical basis, that contributes new knowledge to the field of breeding and is not species-bound. This facet is subdivided into statistical, genetic and economic areas of theoretical development.
Statistical: New concepts and procedures in statistics have been contributed by animal breeders over time. These are in part the result of dealing with large volumes of nonorthogonal data. The development of the selection index by Hazel and Lush (1942) opened new vistas of theoretical development.
Crossbred market swine are the rule in commercial production
Recently, Henderson (1972, 1975) has consolidated work that extends statistical theory to the estimation of random variables and the estimation of maximum likelihood estimates of fixed effects. It utilizes selection index concepts along with those of least squares. This new theory is currently being used in dairy and beef sire evaluation. This area of statistical estimation is being actively pursued, as evidenced by the work of Freeman (1973) and Powell et al. (1975). The development by Harvey (1960) of least-squares analysis of data with unequal subclass numbers and his subsequent writing of analysis programmes have been utilized by breeders and are responsible for considerable statistical sophistication in the breeding literature.
Genetic: The bulk of the theoretical papers in this area are really oriented toward population genetics rather than strictly toward breeding. The work of Fitzhugh and Taylor (1971) in developing theory to interpret growth by using concepts of degree of maturity and mature size have made a contribution to the study of new germ plasm having a large range of mature sizes. Work on growth curve estimation, as illustrated by Brown et al. (1974), has added a new dimension to the study of one of the more important economic traits of livestock production. The concept of complementarity defined by Fitzhugh et al. (1975) completes the development of a sound theory for crossbreeding. Complementarity involves introducing into a crossbreeding system breeds that complement each other in the production of a sound maternal strain and a market animal.
Genetic simulation using computers, as exemplified by Fraser and Burnell (1970), is not at present an active area of investigation in breeding, but the use of computer simulation with linear models and the breeding value concept have been adopted extensively to teach and demonstrate genetic principles. Some research in developing breeding plans has been undertaken recently. Theoretical work on selection response continues, as illustrated by the work of Hill (1974) and Olliver (1974).
Economics: The “big boom” facet of animal breeding today is in the area of economic integration. Monetary values are being involved in what used to be an area where genetic change per year alone was the criterion of choice among programmes. Hill (1971) looked at discounted cashflow concepts in his appraisal of investments in national breeding programmes. This concept has been applied to many situations recently. Dickerson et al. (1974) have examined selection criteria for efficient production by using economic inputs. Pearson and Freeman (1973) looked at profitability in dairy operations rather than at those making the most rapid genetic change.
Probably the most detailed work of combining linear programming from economics to the development of livestock systems analysis has come from Texas. Long et al. (1975), Fitzhugh et al. (1975) and Cartwright et al. (1975) have reported work in this area. Morris et al. (1975) at Guelph are also doing work with systems analysis.
This integration of economics in livestock production theory has done several things in the field of breeding. First, and probably most important, it has clearly isolated areas of biology, including some in breeding, in which little if anything is really known. Some of these areas are now receiving attention in well-designed projects. Second, it has given real economic importance to segments of production that before have received little if any attention from the breeder. The best examples is the cost of animal size in the breeding herd. This area of animal breeding (or more correctly, the contribution of breeding to the study of livestock systems) will expand in emphasis in the future. There are many concepts in economics that take large numbers of variables into account in the optimization process that can be utilized to build a new facet in animal breeding theory.
A freeze branding demonstration
Animal research in breeding
Research in this area is being conducted by universities, government organizations and, to a small extent, by the several livestock industries themselves. It is convenient to consider this research under laboratory animal research and large animal research.
Laboratory animal research: Numerous selection studies continue to be reported, such as those of Orozco and Bell (1974), Bell and Burris (1973), Falconer (1973), Frahm and Brown (1975) and Bateman (1974). Also, Bohren (1975) has dealt with the design of selection studies for specific objectives. In general, these studies continue to confirm existing theory. Some problems still need clarification, particularly those concerning correlated response.
Maternal effects have been extensively studied by using laboratory organisms, especially mice. This work is exemplified by that of Hanrahan and Eisen (1974) and by several theoretical studies by Eisen on maternal effects. Bradford et al. (1974) have examined egg transfer, and Sanders et al. (1975) have looked at Falconer's maternal effect model in cattle. Meyer and Bradford (1974) have investigated the reproductive complex, as have earlier studies of Falconer with mice. Because the reproductive complex becomes increasingly more important economically in species with a low reproductive potential, pilot work in this area of reproduction genetics may be fruitful and of major importance to the livestock industry.
Large animal research: In the United States several regional large animal research projects were initiated after the Second World War, with most midwestern universities contributing. The fruits of these projects have been utilized by the respective industries. Many universities, and especially the U.S. Department of Agriculture, have large animal breeding projects in progress.
These studies have involved determining the amount and kind of genetic variation for traits of economic importance and evaluating the effects of inbreeding and crossbreeding. Koch et al. (1974a, 1974b) reported on a beef cattle selection study that is still in progress. Bereskin et al. (1974) presented some of the results from the classic high-low selection study for backfat in swine. These studies and others in progress tend to confirm earlier theoretical work.
As noted above, the most economically important class of traits is the reproductive complex. The role of heredity in reproduction has been considered by Zimmerman and Cunningham (1975), Laster (1974), Pumfrey et al. (1975) and Rankin and Okidi (1975). Work on the introduction of more prolific breeds of sheep into the United States has been reported (e.g., Price and Ercanbrack, 1975).
Among the more important areas of current research is new germ plasm evaluation in sheep and cattle. Since 1967, when importation of this germ plasm into the United States became possible from Canada, the beef industry in particular has felt the need for research that compares and characterizes the new breeds under United States management situations. The new U.S. Department of Agriculture research station at Clay Centre, Nebraska (the U.S. Meat Animal Research Centre, known as U.S. MARC), has undertaken a massive project to do this evaluation. Its latest report (1975) compares a number of the newly introduced European draught and dual-purpose breeds with the traditional Hereford and Angus breeds under United States management conditions. The speed with which these reports are utilized by the beef industry in real decisionmaking is remarkable.
The backfat probe developed by Hazel in 1952
The important of beef cattle that differ in rate of maturity and eventual mature size has prompted the animal breeder to investigate genetic comparisons under several alternative environments, and not just one as had usually been done. The germ plasm evaluation project involves three slaughter ages for each of the breeds compared. Work of Anderson (1975) and other workers involved in evaluating dairy breeds in beef production suggests that unless managed carefully (by feeding more energy at appropriate times), the dairy breeds fail to rebreed adequately compared with the traditional beef breeds. Again, this involves matching the breed and the environment for compatibility.
As always, studies on inheritance and on ways to eliminate deleterious single genes from populations of livestock are under way. The work of Christian (1972) with pale, soft, exudative pork muscle and the porcine stress syndrome in swine, and of Kieffer et al. (1972) with the double muscle syndrome in cattle, are examples.
Some genetic work is still being done with blood antigens and other aspects of physiological genetics, as indicated by the studies of Bryan et al. (1975) on the cattle histocompatibility system.
Because of the genetic capabilities of large poultry breeding firms, university work in poultry breeding has developed more basic projects (e.g., Nordskog et al. 1974).
Application of animal breeding
A new applied field must first generate enough knowledge from research and develop enough trained people before it can have an impact on the industries in which it is to be applied. Such has been the case with animal breeding.
Little real application of population genetics theory was made to domestic livestock until after the Second World War. Since then, several livestock industries have been revolutionized and the larger species with lower reproductive potential are now yielding to the impact of breeding technology. Large breeding organizations are well-established in poultry; although there are not many of them, they control the genetics of both broiler and egg production. The swine industry has not gone this far, but at least two organizations are involved in swine breeding. Swine testing stations are now an integral part of the industry. Dairy cattle breeding, because of the early use of artificial insemination, has developed a complex of strong bull studs, nearly all of which have young sire sampling programmes and, as such, are taking a real lead in dairy breeding.
The use of Dairy Herd Improvement Association records has become quite sophisticated, with cow as well as sire evaluations being made on several sets of relative groups combined into a selection index. Beef cattle breeding has just begun to have an impact on the very traditional beef industry. There are now 11 breedwide national sire evaluation programmes. Data from these are being analysed with the procedures of estimation developed by Henderson (1972). At least three breeds provide estimates of breeding value on individual animals in their performance programmes. Performance pedigrees are now in vogue.
But possibly the most unique aspect of beef breeding is the Beef Improvement Federation which is a federation of organizations conducting performance programmes in the beef industry. Through this federation, guidelines for establishing performance and sire evaluation programmes and for measuring and recording traits are established. Most organizations conform to these guidelines, which have been developed by animal breeders engaged in research and/or extension work. The Beef Improvement Federation provides the perfect vehicle for animal breeding to be applied in an industry. The United States breeds have responded to the performance challenge rather better than Lerner and Donald (1966) earlier supposed. While this application of breeding technology has been going on in the United States, more exciting largescale breeding programmes have been launched in Europe.
The classic work of Skjervold (1966), dealing with selection schemes and artificial insemination, has now been applied by Skjervold and his associates on a national scale in dairy cattle breeding in Norway. With the advent of the Meat and Livestock Commission in the United Kingdom, national as well as breed schemes have been developed, and some are being applied. Three scientific study groups have made comprehensive reports on the swine, beef and sheep industries. These groups contained both theoretical and applied animal breeders who reported on alternative breeding schemes and made recommendations on those most likely to bring a profit to the industry. Other European countries also have national breeding schemes for cattle, swine and sheep. In time, these programmes can yield valuable information to the store of breeding knowledge.
Animal breeding, as an applied field of population genetics, is endowed with a mathematically sound theory developed early in its history. Both theoretical and applied problems in breeding remain to be solved, although they are not as obvious as was once the case. Real opportunities exist for the animal breeder who is willing to make use of new knowledge generated in other areas of genetics and of the store of theory developed in economics. Even with reduced research funds it will be possible to serve the livestock industry creatively, especially when industry itself can develop a suitable data base.
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