Behaviour, stress and welfare of Sprague Dawley rats (Rattus norvegicus) on diet board feeding for 24 months

Abstract Diet board (DB) feeding aims to reduce the health hazards associated with ad libitum (AL) feeding. Rats have to gnaw wood to detach food from the DB, reducing their food consumption. We studied the welfare effects of DB by measuring faecal corticosterone metabolites (FCM), elevated plus-maze (EPM) behaviour and cage behaviour. In this two-year experiment, 147 group housed (n = 3) Hsd:Sprague Dawley® male and female rats were subjected to DB or AL feeding. DB feeding in females elevated FCMs and increased eating observations by 85%. The DB males were observed eating 30% more often and resting 4.2% less than their AL counterparts. The DB rats of both sexes had 19% increased cage exploration during daytime and 20% reduced grooming during night-time compared to the AL rats. The increased FCMs may indicate slight stress in DB females. The EPM results indicate there was no anxiety due to DB feeding at six months. The cage behaviour could point to mild chronic stress in DB rats, but the lack of effect on escape-related behaviour and agonism suggests that there were no substantial welfare problems. DB feeding did not seem to disturb the circadian rhythm. The smaller food requirements of DB females meant they had to sacrifice less time than males gnawing at the DB to satisfy their appetite