Porcine stress syndrome caused by a ryanodine receptor gene mutation was selected into pig populations for leanness, causing preventable suffering before the genetic basis was identified.
Porcine stress syndrome illustrates how genetic selection for production traits can inadvertently introduce severe welfare problems. The suffering of pigs dying from malignant hyperthermia episodes was a foreseeable consequence of selection pressure — foreseeable once the genetic basis was understood, but the connection between leanness and stress susceptibility was not initially apparent. The successful elimination of the halothane gene through genetic testing demonstrates that welfare-compromising genetic traits can be removed once identified. Proactive genetic welfare screening should be standard in livestock breeding programmes.