The importance of reward-evaluating mechanisms for animal welfare

Abstract

An increasing need exists for tools to assess and improve animal welfare in an objective and scientifically based manner. This review presents an overview of knowledge and factors related to animal welfare, and explains a new concept to approach animal welfare research. This concept is based on reward-evaluating mechanisms in the brain and states that welfare is determined by the balance between positive and negative experiences. This implies that an interaction exists between stress- and reward-systems in the brain, and as a consequence: I. negative experiences induce an increased sensitivity (need) for positive experiences. II. negative experiences can be compensated by positive experiences. In this line of reasoning, reward-related behaviour is proposed to be an important tool to measure and improve animal welfare. Based on this, two uses of reward-related behaviour can be hypothesized: I. reward-sensitivity may be a tool to assess the state of an animal in terms of welfare, since it can be indicative of the current state of the balance that is dependent on previous (stressful) experiences. II. regular presentations of rewards may serve as a tool to counteract stress thereby moving the balance to the positive side and, thus, to improve welfare. This has been investigated by using the rat as a model and reward-sensitivity is determined by the spontaneous behavioural response an animal shows in expectation of a reward (i.e. anticipatory behavior). A third use of reward-related behaviour comes from the fact that anticipatory behaviour is influenced by the (rewarding) properties of the forthcoming reward (or other event), and thus, III. may serve as a tool to assess animal perception of this reward/event.

A descriptive overview is given of the evidence obtained thus far for the proposed uses of reward-related behaviour. The biological background of the presented concept of welfare can be generalized to all (vertebrate) species and anticipatory behaviour can be evoked in a wide range of other species. Therefore, this tool to measure and improve welfare of captive animals has great potential.