Boissy, A., Manteuffel, G.
, Jensen, M. B., Moe, R. O., Spruijt, B., Keeling, L. J., Winckler, C., Forkman, B., Dimitrov, I., Langbein, J., Bakken, M., Veissier, I. & Aubert, A. (2007).
Assessment of positive emotions in animals to improve their welfare.
Physiology & Behavior,
92, 375-397.
https://doi.org/10.1016/j.physbeh.2007.02.003