Dynamic selection for sheep genetic improvement

Dynamic selection is a process used in livestock improvement programmes to maximise genetic progress while constraining the long term rate of inbreeding. An optimisation algorithm identifies proportions of genes each selection candidate should contribute to the next generation. Application of dynamic selection procedures to select cull and replacement ewes, and then subsequently to select a ram team, was demonstrated using data from a Romney sheep breeder. When compared with selection based on an index of breeding values alone, dynamic selection of cull and replacement ewes reduced the accumulation of relatedness by approximately 85% of the average annual accumulation from 1994 to 2000. To achieve this, approximately 33% of the average annual genetic progress in average index value was sacrificed. Using dynamic selection to identify a ram team to be mated to selected ewes resulted in a saving in relatedness by an amount equal to the average annual accumulation from 1994 to 2000 with only a very modest drop in genetic progress of 9% of the average annual genetic progress in average index value. This study has demonstrated that dynamic selection tools could, when practically applied to sheep breeding populations, provide a transparent and efficient means of managing the tradeoff between rate of genetic progress and rate of accumulation of relatedness.