Genetic selection profoundly affects pig welfare—selection for production traits can inadvertently compromise welfare, while targeted selection for welfare traits can improve welfare across millions of individuals over generations.
Decades of selection for lean muscle deposition, growth rate, and feed conversion efficiency have produced highly productive pigs with associated welfare challenges: porcine stress syndrome (PSS) in Pietrain and Hampshire breeds was caused by the halothane gene before genetic testing eliminated it; high-growth-rate sows face increased cardiovascular strain; and selection for high muscle mass has contributed to increased osteochondrosis and locomotion problems. These examples illustrate how narrow production-focused selection can create welfare trade-offs requiring correction.
Tail biting has genetic components—some lines are more predisposed to biting or to being bitten. Research in Norway and the Netherlands has demonstrated genetic variation in tail biting propensity, with estimated heritabilities of 0.15-0.30. Incorporating tail biting resistance into selection programmes, combined with management improvements, could reduce this welfare problem across populations over time. Genetic approaches complement but do not replace management interventions.
Genetic selection for disease resistance and general robustness improves welfare by reducing the frequency and severity of health problems. Genetic resistance to PRRS (Porcine Reproductive and Respiratory Syndrome) has been identified in some lines; genomic selection incorporating health and robustness traits alongside production traits creates pigs with better welfare profiles across their lifetime. Norwegian and Dutch pig breeding programmes have explicitly incorporated welfare traits into selection indices.
Selection for hornlessness (polled genetics) in naturally horned pigs eliminates the welfare costs of tusk removal in boars. While tusk removal is less common than dehorning in cattle, similar welfare principles apply—genetic approaches that eliminate the need for painful procedures represent superior welfare outcomes to managing the consequences of traditional genetics.