Simulation of Genetic Changes in Life Cycle Efficiency of Pork Production. III. Effects of Management Systems and Feed Prices on Importance of Genetic Components

A deterministic, bioeconomic simulation model of pork-production efficiency was used to predict effects of alternate management systems and feed prices on relative importance of several genetic traits for unspecialized swine populations. Traits considered were increased number born alive (NBA), preweaning viability (VIAB), growth rate (GR) and lean growth rate (LGR) and decreased age at puberty (−PUB), percentage fat at 100 kg (−%F) and fat growth rate (−FGR). Independent unit genetic standard deviation changes in the means of each trait were used to simulate effects on four measures of input/output efficiency (H): Mcal ME (metabolizable energy)/kg carcass lean (H1), Mcal ME/kg empty body weight (H2), cost/100 kg carcass lean (H3) and cost/100 kg live weight (H4). Management alternatives were length of farrowing interval, sale weight, marketing by weight or age and doubling feed prices. System efficiency was improved for all Himeasures by reducing farrowing interval from 192 to 157 d. Increasing sale weight reduced biological efficiency (H1and H2), but improved economic efficiency (H3and H4). Longer farrowing intervals or lower sale weights increased relative importance of reproductive traits and decreased importance of growth traits, but left ranking of traits unchanged. Marketing by age rather than weight permitted greater genetic improvement in economic efficiency from increased GR and LGR by spreading sow costs over more weight of pig or lean marketed, without increasing feed costs. Doubling feed prices decreased relative importance of NBA and VIAB for H3and H4 and magnified adverse effects of −%F, LGR and −FGR for H4. Optimal balance among breeding objectives will shift with future management-marketing systems.