The effect of exercise and stress on equine learning, memory and welfare.

This project investigated the effect of stress and exercise on domestic horses’ (Equus caballus) learning and memory of industry-type negatively reinforced training tasks, applying a ‘broad brush’ translational neuroscience lens to the findings. Horses are routinely exposed to stressors as well as physically demanding activities. Many owners report unwanted behaviours, some of which may be dangerous and a welfare risk for horses. Based on the literature in other species it is likely these may be the result of stress-induced effects on the neural processes serving learning, memory and cognition. In addition, very little is known of the effects of exercise on equine cognition, including whether it confers benefits as has been observed elsewhere.
To explore these issues, two experiments were undertaken to evaluate the effects of stress and exercise on equine cognitive outputs of direct relevance to industry, using stressors that were analogues of those that domestic horses are likely to encounter. In addition, proxies for neurotransmitters of known relevance to learning and memory were assessed: heart rate (proxy for noradrenaline), salivary cortisol (proxy for brain cortisol), as well as serum Brain derived neurotropic factor (BDNF) (proxy for brain BDNF).
Horses were exposed to either acute exercise, psychosocial stress or inactive treatment prior to learning (Chapters Three and Four) or chronic heterotypic psychosocial stressors or control treatment after completing the first of two learning tasks and then given a second learning task requiring cognitive flexibility after the treatment (Chapters Five) and their acquisition and memories of the learning tasks were evaluated. The acquisition of avoidance responses and behaviours indicative of affective state were also assessed in relation to learning acquisition and cognitive flexibility (Chapter Six).
Due to the current lack of precision for assessing the neural correlates of equine cognition, the analysis is necessarily inferential; however it mirrors the methodologies used in many human cognitive neuroscience studies. Acute exercise that caused moderate increases in salivary cortisol and heart rate during learning enhanced the acquisition of learning compared to horses exposed to stress or inactivity (Chapter Three). The effect of pre-learning stress or exercise on memory consolidation is less clear, though it appear some form of physiological arousal may be beneficial (Chapter Four). The chronic stress exposure (Chapter Five) significantly increased salivary cortisol but not serum BDNF concentrations, but contrary to expectations did not impair cognitive flexibility. However, in a subset of the stress exposed horses, the combination of an ethologically challenging learning task and the chronic stress exposure impaired their consolidation and/or retrieval of the cognitive flexibility task, leading to a higher number of perseverative errors. Lastly, despite learning to avoid the aversive stimuli used in the learning tasks, behaviours indicative of a negative affective state did not universally decline as expected, suggesting that aversive training methods, even when applied as recommended can carry welfare risks (Chapter Six).
These studies are the first to report in horses that moderate exercise can enhance learning and memory and that in some situations, exposure to chronic stress can impair cognitive flexibility memory retrieval. They also provide evidence that high cortisol concentrations may impair the acquisition of learning, possibly due to cortisol’s effects on brain regions relevant for learning. In addition, the translational neuroscience approach taken here has revealed novel interpretations of equine learning behaviour that could assist trainers to improve their practice and safeguard their horse’s welfare. For example, trainers could purposefully include a short exercise bout as a cognitive enhancer prior to a training session. Alternatively, when planning sessions that will require cognitive flexibility of the horse, trainers should be aware that stressors arising from training and environmental factors may impair the horse’s ability to learn, and adjust their training goals accordingly.