This scientific opinion addresses animal welfare aspects of slaughtering of livestock pregnant animals.Term of Reference (ToR) 1 requested assessment of the prevalence of animals slaughtered in a criticaldevelopmental stage of gestation when the livestock fetuses might experience negative affect. Limiteddata on European prevalence and related uncertainties necessitated a structu red expert knowledgeelicitation (EKE) exercise. Estimated median percentages of animals slaughtered in the last third ofgestation are 3%, 1.5%, 0.5%, 0.8% and 0.2% (dairy cows, beef cattle, pigs, sheep and goats,respectively). Pregnant animals may be sent for slaughter for health, welfare, management andeconomic reasons (ToR2); there are also reasons for farmers not knowing that animals sent forslaughter are pregnant. Measures to reduce the incidence are listed. ToR3 asked whether livestockfetuses can experience pain and other negative affect. The available literature was reviewed and, at asecond multidisciplinary EKE meeting, judg ements and uncertainty were elicited. It is concluded thatlivestock fetuses in the last third of gestation have the anatomical and neurophysiological structuresrequired to experience negative affect (with 90–100% likelihood). However, there are two differentpossibilities whether they perceive negative affect. It is more probable that the neurophysiologicalsituation does not allow for conscious perception (with 66–99% likelihood) because of brain inhibitorymechanisms. There is also a less probable situation that livestock fetuses can experience negativeaffect (with 1–33% likelihood) arising from differences in the interpretation of the fetalelectroencephalogram, observed responses to external stimuli and the possibility of fetal learning.Regarding methods to stun and kill livestock fetuses at slaughter (ToR4), sets of scenarios andrespective actions take account of both the probable and le ss probable situation regarding fetal abilityfor conscious perception. Finally, information was collated on methods to establish the dam’sgestational stage based on physical features of livestock fetuses (ToR5).