The effect of artificial breeding on the rate of genetic improvement of butterfat yield in Victorian jerseys

Although the subject of this thesis is limited to the effects of Artificial Insemination on the Victorian dairy cattle population this review of the literature covers a far wider range of material, reporting on investigations not only of the basic genetic parameters of dairy production to provide. the necessary framework on which to base considerations of the effects of artificial insemination, but also to outline the theoretical researches on which any discussion of the future of artificial insemination must be based. In Victoria dairy farmers are paid for their milk on the basis of butterfat production, except in some areas where part of their output is used for town milk supply. However in the future it is probable that the basis of payment will change to one involving butterfat and another milk constituent, probably protein. This review deals only with the parameters of milk and butterfat production with some passing reference to the production of milk protein. The basic concepts of population genetics applicable to this topic viz., metric variation, the relevant genetic parameters, selection and inbreeding, are discussed as the background for discussion of the value, techniques and optimization of artificial breeding dairy cattle and the effect of inbreeding on these. Also included is a short history of artificial breeding and a discussion of the limits to genetic improvement in dairy cattle. Considerable literature has been written on the subject of selection for genetic improvement in dairy cattle, but very little work has been done in Australia. Most of the information cited in this review has therefore been derived from overseas literature, much being from the Northern Hemisphere. This produces somewhat of a problem because differences in housing and management between Australian, and specifically Victorian, open-range grazing and the intensive winter-housed systems common in the Northern Hemisphere, give rise to differences in breeding aims and economic efficiencies