animalbiosecurityconferenceconsiderationsdensitydiseasedreconomicseditionfarmfinishgeneralgilthealthheatimpactimportanceindustrylongevitymanagementminimortalitynichepeoplepigsporkproducersproductionprogramprrsreduceresearchseasonseriessowspecialstepsstockingstresssurvivabilitysustainabilityswineunderstandingventilationwaterwean