Malmkvist, J., Díez-León, M., Christensen, J. W. 2024. Animals with various forms of abnormal behaviour differ in learning performance and use of enrichment: Evidence from farm mink. Applied Animal Behaviour Science 271, 106167.

Abnormal behaviour has been related to differences in cognitive function and reduced animal welfare. However, these associations are understudied, and little is known about how various forms of abnormal behaviour affect learning performance, stress responses and use of enrichment. We tested the hypotheses that different forms of abnormal behaviour are (1) associated with various degrees of impairment of learning, (2) generally related to elevated stress responses including fearfulness, and (3) reduced during periodical access to running wheels using American mink (Neogale vison, synonym Neovison vison) as model species. Farm mink were screened into groups displaying no apparent abnormal behaviour (NONE, n=35), or abnormal behaviour as fur-chewing (FURCHEW, n=21), Stereotypic Behaviour (SB) i.e., pacing (PACERS, n=33), stationary SB (STATSB, n=22), licking SB (ORALSB, n=17), and combination of forms (MIXED, n=22). Learning performance was assessed in a two-choice visual discrimination test with three progressive stages: 94% passed the 1st (acquisition), 70% the 2nd (recall) and 42% the 3rd (reversal) stage. Mink from groups MIXED and PACERS passed more learning stages than ORALSB and NONE mink (MIXED 2.3a; PACERS: 2.1a; ORALSB 1.4b; NONE: 1.4b, F5,83=2.7, P=0.027), while the other groups did not differ significantly (STATSB: 1.9ab, FURCHEW: 2.0ab). Thus, the most locomotory active forms of abnormal behaviour appeared associated with enhanced learning. NONE mink spent more time in investigative sniffing (13 ±1.6 s) than did mink with abnormal behaviour (6 ±0.9 s) in a 30 s temperament test (F5,144=3.2, P=0.010). A large individual variation in faecal cortisol metabolite levels rendered this indicator insensitive to detect group differences. When given access to a running wheel, the groups differed in activity (F5,131=10.0, P<0.001): Revolutions per day, MIXED: 1929a, STATSB: 1445a, PACERS: 1435ab, ORALSB: 466bc, FURCHEW: 485c, and NONE: 344c. All forms of SB, except licking, were significantly reduced (P<0.001) during running wheel access. Thus, licking SB appears different from the other SBs. In conclusion, different forms of abnormal behaviour appear associated with different cognitive and motivational characteristics. Further, our results suggest a potential positive link between physical activity (even if it is stereotypic) and learning.