Section 1, the main part, provides evidence of genetic variation in the concentration of copper in the blood, liver and brain of sheep and of breed variation in the incidence of disorders associated with copper metabolism. Evidence of a less detailed kind is also presented of genetic variation in the concentration of other minerals in the blood of both sheep and cattle. The studies also contribute information on the magnitude of several non-genetic sources of variation in mineral concentrations.
This work provides a basis for the hypothesis that heredity partly controls the nutritional requirements of ruminants for minerals,including 'trace' elements. It suggests that by taking the genetic variation into account it should be possible to formulate the nutritional needs of the animals more accurately than otherwise and thus help to optimise the efficiency of animal production. The work suggests that it may also be possible to breed animals for adaptation to mineral deficiencies or excesses, or for resistance to metabolic disorders. The work demonstrates, in this facet of animal production,the inter-relationship of genetics and nutrition in the maintenance of animal health.
Section 2, of the thesis deals with more general studies on cattle and sheep and is concerned with the apportionment of variation to genetic and non-genetic sources for a variety of traits related to performance and survival. Some of these experiments provided the initial genetic evidence, and later the necessary opportunities, for exploring variation in mineral metabolism.
Section 3 deals with the structure and dynamics of breed organisation and the way these affect the potential for genetic improvement of livestock. This work was undertaken before experimental facilities had become available to the author. Much of the data used for the cattle papers (Nos. 38-^2) in this section contributed to the author's Ph.D. thesis in 1950.