Welfare assessment in laboratory animals has historically focused on negative indicators of suffering, but the development of positive welfare measures is changing how good welfare is defined and assessed.
Positive welfare assessment moves beyond the question of whether animals are suffering to ask whether they are thriving. An animal that is not obviously sick, not stereotyping, and not showing obvious pain may still have a quality of life far below what is possible with better housing, enrichment, and social provision. Rats that produce 50 kHz ultrasonic vocalizations during play are signaling active positive emotional states. Mice that burrow vigorously are expressing natural motivation unimpaired by pain or illness. Developing and implementing these positive indicators alongside conventional negative measures provides a more complete picture of laboratory animal welfare and identifies opportunities for improvement that negative-only assessment misses.