ECONOMIC VALUES OF TRAITS FOR PIG IMPROVEMENT .1. A SIMULATION-MODEL

A computer model simulating life cycle production of a breeding sow an d growth performance of her offspring was developed to estimate econom ic values of reproduction and growth performance traits. A biological growth model, simulating the digestion and metabolism of dietary nitro gen in growing pigs (20 to 85 kg), was part of the life cycle model. T he growth model was based on the linear/plateau relationship between d aily protein deposition and digestible energy intake. A farrow-to-fini sh production system, with slaughter pigs marketed at fixed liveweight s, was simulated. Input variables were: gilt age at first oestrus, wea ning to oestrus interval, number of pigs born alive per litter, and pr e-weaning mortality for each parity. Economic inputs included prices o f feed ingredients, carcass returns and non-feed costs. The upper limi t to body protein deposition rate, mean daily ad libitum digestible en ergy intake and minimum lipid to protein deposition ratio were assumed the major genetic determinants of pig growth. The model output includ ed average daily gain, ad libitum daily feed intake, backfat thickness , and life cycle reproductive performance and profit. The combined lif e cycle profit was expressed in the form of an Annualized Present Valu e. Life cycle profit was calculated for a range of simulated pig genot ypes.