Animals are exploited by man for several different purposes. According to many, society should be concerned about the welfare of these animals. Currently, an increasing need exists to be able to assess and improve animal welfare. In this thesis a concept of welfare is applied that states that `welfare is determined by the balance between positive and negative experiences`. This definition implies that an interaction exists between stress- and reward systems in the brain and that negative experiences can be compensated by positive experiences. This thesis describes a study that investigates whether the spontaneous behavioural response that animals display when they expect a reward (anticipatory behaviour) can be used as a welfare indicator. This concept is based on existing knowledge about the influence of previous experiences such as stress on the sensitivity for rewards in both man and animals. The response (i.e. sensitivity) to rewards can therefore be indicative of previous experiences and may therefore be a tool to assess the state of an animal in terms of welfare. In this study the rat is used as a model and reward-sensitivity is determined by anticipatory behaviour which is evoked in this animal by classical conditioning. This means that through regular pairings of a stimulus (sound and/or light) with the arrival of a reward, the animal will form an association between this stimulus and the reward. Subsequently, the animal will display anticipatory behaviour at the presentation of the stimulus. This behavioural response can be investigated in the interval between the announcement and the actual arrival of the reward and is characterised by an increase in activity.


CONTENTS

1 General introduction
2 Access to enriched housing is rewarding to rats as reflected by their anticipatory behaviour
3 A simple enriched cage for laboratory rats reduces aggression, enhances activity, and influences behaviour on the elevated plus maze
4 Standard housed rats are more sensitive to rewards than enriched housed rats as reflected by their anticipatory behaviour
5 Effect of housing condition on reward sensitivity as assessed by breaking-point tests and anticipatory behaviour
6 On the relationship between stimulus-induced anticipatory behaviour and stimulus-induced instrumental responding for a reward
7 Announced rewards counteract the impairment of anticipatory behaviour in socially stressed rats
8 The efficacy of announced reward on counteracting the effects of chronic stress on behaviour and hippocampal plasticity
9 General discussion