The accepted norm in most laboratories around the globe is feeding laboratory mice an ad libitum diet, although several health impairments are well-established. In contrast, reducing the animals' body weight by feeding them less food once per day (referred to as 24 h schedule) has been shown to enhance life span and reduce disease susceptibility. Against this background, this study aimed at systematically investigating the effects of different feeding routines. Therefore, three feeding routines were compared to the standard ad libitum feeding and effects on body weight development and welfare were investigated in male C57BL/6J mice. In particular, a 24 h schedule group, an AUTO group, characterized by an automated supply of small pieces of food all over the day, and a 4 h removal group, characterized by daily removal of food for 4 h, were studied. While the removal of food for 4 h per day did not lead to a reduction of body weight, and hence is unlikely to prevent negative effects of overfeeding, both the 24 h schedule group and the AUTO group led to the aspired body weight reduction. In the AUTO group, however, higher levels of corticosterone metabolites and stereotypies were observed, implying a rather negative impact on welfare. By contrast, no distinct negative effects of a 24 h schedule were found. Studies like this underline the general need for evidence-based severity assessments of any procedure involving living animals.

When confronted with ambiguous information, some individuals respond as expecting positive and others as expecting negative outcomes. Based on such decisions in ambiguous situations, a behavioural test was developed in animal welfare science that allows researchers to characterise animals as more “optimistic” or “pessimistic”. Recent studies using this judgement bias test detected consistent individual differences in “optimism levels”. However, the ecological and evolutionary relevance of these differences is not yet clear. In this proof-of-principle study with laboratory mice, we aimed to explore the potential ecological consequences of being more optimistic or pessimistic. Specifically, we investigated whether “optimists” make different foraging choices under predation risk than “pessimists”. To address this, we first characterised female mice (C57BL/6J) as more optimistic or pessimistic by using two established judgement bias tests. Then we assessed individual differences in the tendency to choose high-risk/high-reward or low-risk/low-reward conditions by using a newly developed test based on predator cues (rat odour). We show that this novel test is a suitable tool to investigate individual differences in ecologically relevant risk-taking: First, the test imposed a risk-foraging trade-off for mice because the risky condition clearly induced more avoidance and risk assessment. Second, individuals showed highly repeatable differences in their choice of the risky or safe option. Considering our main aim, we did not find evidence that optimistic and pessimistic mice make different foraging decisions under predation risk. A potential explanation is that optimists, although expecting positive outcomes, might not take more risks when it can jeopardise their survival.