Successive negative contrast: An appropriate approach to measure affective state in dogs?

Successive negative contrast (SNC) is a decrease in response when animals unexpectedly face reward devaluation to levels below those of animals always receiving low-value rewards. SNC appears to be influenced by background affective states and has thus been proposed as a tool for assessing animal welfare. While reported in several mammal species, findings of SNC in dogs (Canis lups familiaris) have been inconsistent. This study aimed to investigate the suitability of SNC to assess affective states in dogs. For this purpose, it is important that the test can be consistently used across populations, and we therefore tested the reaction to reward devaluation in laboratory, shelter, and owned dogs (n = 12 per population). After assessing individual food preferences, reward devaluation tasks were performed where animals first solved a puzzle toy for high-value rewards (pre-shift), then for low-value rewards (post-shift), and again for high-value rewards (re-shift). Results showed that shelter dogs and three owned dogs removed fewer cones of the puzzle, ate fewer rewards, and took longer to complete the task (remove all cones) in the post-shift phase compared to pre- and re-shift phases. Conversely, no reduction in number of cones removed nor in number of rewards eaten was found for laboratory and the remaining nine owned dogs. The behaviour of the first group (response reduction following reward devaluation) is consistent with SNC, whereas the behaviour of the second (no change in behaviour after reward devaluation) is not. The inconsistency of SNC within and across dog populations raises questions regarding its suitability for evaluating dog welfare.