Animal affect - from short-term to long-term states

Overview & Synopsis

In human literature, there is evidence that short-term emotions can have cumulative effects on longerterm states, and we are beginning to understand the effect of time on animal emotions. For simplicity, we can consider emotions as short-term states that may build into longer-term, free-floating moods, which together may contribute to an even longer, perhaps lifelong, state. There are assumptions associated with these three states that can be empirically studied. For example, emotions may fluctuate due to memory, prediction errors or contrast effects. Not only may emotions build into moods, but moods may affect an emotion, or perhaps animals feel mixed emotions in some situations. There may, as in humans, also be a higher level of integration such that emotions and moods integrate into a longer and more stable state (e.g., affective happiness). Here, we present two categories of methodologies that could help us evaluate the cumulation of animal affective states, and thus welfare, over long periods. They were primarily developed in human research, and our groups are working to propose new methods, or frameworks, applicable for animals, especially farmed animals. One method (neurophysiological markers of cumulative affect) is to measure how affective states cumulate within the body of an animal. For example, telomeres may help describe the aging process, and hippocampal size may reflect brain plasticity. Based on 11 criteria, the following indicators may help us understand cumulative affect: changes to telomeres, epigenetics, oxidative stress, immunity function, the gut microbiota and hippocampal size. A second method (affect balance) is to estimate the proportion of time an individual is in a positive or negative state by sampling emotional experiences over time, or, in humans, self-reports of how often in a period a person felt a specific emotion. These samples can then be subtracted (positive – negative affect) or divided (positive/negative affect) or taken to form categories to estimate the affect balance score. This score may reflect welfare (in animals) or longer-term states such as happiness (in humans). The theoretical study of timing of affect and these two novel categories of methodologies pave the path towards the understanding and assessment of positive animal welfare, specifically evaluating ‘predominantly positive mental states’ ‘over different timescale