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Der Züchter

, Volume 37, Issue 7–8, pp 309–323 | Cite as

Modern problems of population genetics in animal husbandry

  • J. S. F. Barker
Article

Summary

Knowledge in animal husbandry derives from a complex of disciplines, and in this review the theory of one of these (population genetics) is discussed with regard to animal improvement, but with consideration of its implications in the other disciplines together with contributions from these to animal improvement programmes.

The conventional programme for genetic improvement is outlined, but with particular emphasis placed on the lack of knowledge as to just what constitutes an adequate foundation population and what procedures will provide maximum total response to selection. An adequate foundation population is one containing as wide a sample as possible of the genetic variability existing in the species, and it is argued that genes of low initial frequency may comprise a significant proportion of the genetic variability available to selection. Further, a significant proportion of this variability may result from the segregation of a relatively small number of genes of large effect. The need for detailed information on the nature of gene action determining quantitative variation is emphasised.

Maximisation of foundation population size is of prime importance, while the effective population size in subsequent generations of selection will largely determine total response to selection. Because of the restricted size of breeding programmes, selection responses will generally cease at less than the possible limit, so that methods of breaking through such apparent limits are discussed.

In practical breeding programmes, a number of characters are generally under selection, and improvement then depends on genetic correlations among these characters. But to predict changes under selection, or to interpret those that have occurred, the basic causes of genetic correlations must be understood. Such understanding is further complicated by the possibility of change in magnitude or even direction of a genetic correlation during selection.

Contributions from anatomy, physiology and animal behaviour are discussed in terms of information relevant to the definition of breeding objectives, optimum husbandry techniques, and limits to intensification in animal management. Artificial insemination has revolutionised dairy cattle breeding, and the development of techniques for oestrus synchronisation make more practical its use in other species. The implications of super-ovulation and egg transfer and modification of sex ratio on breeding programmes are considered, and the review concludes with a plea for information on the economics of breeding programmes.

Keywords

Breeding Programme Genetic Correlation Artificial Insemination Oestrus Synchronisation Dairy Cattle Breeding 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Zusammenfassung

Grundlage der Entwicklung der Tierzüchtung sind die Erkenntnisse einer Reihe von Wissensgebieten. In der vorliegenden Übersicht wird über eine dieser Disziplinen, die Populationsgenetik, berichtet, und zwar speziell über die Theorie der Verbesserung von Leistungseigenschaften unter Einbeziehung anderer Disziplinen und ihrer Beiträge zum Tierzüchtungsprogramm.

Es wird das konventionelle Programm für eine genetische Leistungssteigerung skizziert, aber mit besonderem Nachdruck darauf hingewiesen, daß keine genaue Kenntnis darüber besteht, was als angemessene Ausgangspopulation anzusehen ist und welche Maßnahmen den größten Selektionserfolg sichern. Eine angemessene Ausgangspopulation sollte die in der Spezies vorhandene genetische Variabilität im größtmöglichen Umfange enthalten, und es wird die Ansicht vertreten, daß Gene, die in der Ausgangspopulation mit geringer Frequenz vorhanden sind, doch einen signifikanten Anteil der einer Selektion zugänglichen genetischen Variablität ausmachen. Ein weiterer signifikanter Anteil dieser Variabilität dürfte aus der Spaltung einer relativ geringen Anzahl von Majorgenen herrühren. Die Notwendigkeit eingehender Unterrichtung über die Art der Genwirkung, welche die quantitative Variabilität bestimmt, wird betont.

Es ist von primärer Wichtigkeit, die Ausgangspopulation so groß wie möglich vorzusehen, der Selektionserfolg in den folgenden Generationen wird wesentlich durch die vorhandene Populationsgröße bestimmt. Infolge der beschränkten Größe der Züchtungsprogramme erreicht die Selektion in der Regel nicht das Mögliche; Methoden zur Durchbrechung solcher Grenzen werden besprochen.

In praktischen Züchtungsprogrammen wird im allgemeinen auf eine Reihe von Eigenschaften selektiert, die Leistungssteigerung hängt dann von den genetischen Korrelationen zwischen diesen Eigenschaften ab. Um aber durch Selektion zu bewirkende Veränderungen abschätzen oder aufgetretene erklären zu können, ist es notwendig, die Ursachen der genetischen Korrelation zu erkennen. Das wird durch die Möglichkeit von Stärke- oder sogar Richtungsänderungen der Korrelationen während der Selektion erschwert.

Es wird schließlich über die Beiträge anderer Disziplinen, wie Anatomie, Physiologie, Verhaltensforschung, zur Festlegung der Zuchtziele, zu den besten Zuchttechniken und bezüglich der Grenzen einer Intensivierung der Tierhaltung berichtet. Die künstliche Besamung hat eine Revolution in der Rinderzüchtung bewirkt und durch die Entwicklung von Techniken zur Synchronisation des Geschlechtszyklus wird ihre Anwendung auch bei anderen Arten möglich. Es werden die Auswirkungen von Super-Ovulation und Ei-Übertragung sowie der Veränderungen des Geschlechtsverhältnisses behandelt. Die Übersicht schließt mit dem Ersuchen, daß auch über Fragen der Ökonomik von Züchtungsprogrammen informiert werden sollte.

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Copyright information

© Springer-Verlag 1967

Authors and Affiliations

  • J. S. F. Barker
    • 1
  1. 1.Department of Animal HusbandryUniversity of SydneyAustralia

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