ABSTRACT
Having created a founder transgenic animal, further development and application in commercial livestock populations follows four major components: (1) testing of transgene inheritance and effects, (2) multiplication of the number of animals carrying the transgene and creation of a nucleus or elite breeding stock, (3) dissemination of the transgene into the commercial population, (4) continued genetic improvement within the commercial population. The last only applies to those species where genetic selection usually takes place within the commercial population. The testing phase typically will include estimation of hemizygous and homozygous transgene effects on all aspects of economic merit. Difficulties at this stage can be anticipated and become a factor in determining which traits to target and in which lines or breeds to create transgenic animals. Time taken to develop a transgenic nucleus or elite breeding stock will depend on transgene effects, initial genetic lag, the risk from inbreeding depression and structure of the commercial population. Recently developed methods of statistical analysis allow accurate and unbiased estimation of transgene effects concurrent with conventional breeding values which will help in all phases of development, dissemination and utilisation. Relatively modest hemizygous transgene effects, equivalent to a 3–10% increase in performance of key traits will generally be needed to compete genetically with existing genetic improvement programs. Somewhat larger effects will be needed to cover the extra costs of transgenic programs.
