Effect of dairy calf rearing systems on affective states.

Dairy calves are typically reared in environments that differ greatly from naturalistic conditions: separated from their dam after birth, housed without peer contact, and unable to graze or have outdoor access. An improved understanding of the effect of the farming environment on calves' affective states may help refine management practices to improve dairy calf welfare. In this narrative review, we examine how characteristics of dairy calf rearing systems relate to both short- and long-term affective states. Affective states are commonly inferred from behavioral proxy measures (e.g., changes in time budgets, play, etc.) or conditioned responses to affective-state paradigms. We categorized environmental elements through physical, social, and temporal components and discuss the current knowledge on their effects on indicators of affective states. Consistent evidence supports that physical features such as adequate milk allowance, different sources of solid food (e.g., concentrate and forage), soft and dry lying surfaces; and a social environment allowing full contact with conspecifics appear important for promoting positive affective states and reducing negative ones in dairy calves. Although the temporal characteristics of environmental features remain comparatively underexplored, available evidence suggests factors such as timing, predictability, and control can modulate how physical and social components are experienced. Overall, knowledge regarding longer-lasting mood states in dairy calves remains limited. Addressing these gaps through future research could help refine rearing practices that support not only the reduction of negative states, but also the promotion of positive welfare in dairy calves.