Expected relative responses to selection for alternative measures of life cycle economic efficiency of pork production.

Relative genetic responses to selection for alternative measures of economic efficiency of pork production were examined. The analysis was based on results from a deterministic bio-economic model of lifecycle pork production. Alternative aggregate breeding values considered were based on cost (+)/unit of live weight or of carcass output lean for different production systems and for different breeding roles of the selected stocks. For cost/unit of lean, changes in leanness (or fatness) dominated the index. For cost/unit of live weight, however, no one trait dominated the index, and changes in growth and reproductive traits as well as the breeding role of the stock (purebred, maternal or paternal) were important in defining selection objectives. Management and production systems were less important than breeding role for cost/unit live weight output, except that importance of growth rate was increased by marketing at the mean weight reached at a fixed age rather than at a fixed weight irrespective of age. Implications of these results for goals and systems of pig improvement are discussed.