The effect of altering the microbiome on aspects of equine sleep and emotional state and cognitive performance

The gut-brain axis is such that altering the microbiome can have a significant effect on sleep patterns, emotional states and cognitive function (Appleton, 2018). The diets of domesticated and captive animals are often formulated with little or no consideration of how this may impact the gut-brain axis and subsequently on factors that have the capacity to greatly affect the animal’s welfare. The aim of this study was to examine the effects of altering the microbiome in the horse on sleep quantity/quality, emotional state and cognitive performance during a reward-prediction-error task and on blink rate (as a proxy measure for CNS dopaminergic activity). Eight horses were given two balanced diets of low and high starch that have previously been shown to produce a significant difference in the equine microbiome (Bulmer, 2020). Diets were given for 21 days within a balanced cross-over design. During days 19-21, the quantity and quality of sleep that the horses experienced were recorded using a previously defined sleep ethogram (Greening and McBride, 2022) as was blink rate (McBride et al., 2022). During days 20-21, horses were tested on the reward-prediction-error task. This operant task involved training horses to touch visual stimuli in order to gain a food reward. Horses were then placed under two consecutive extinction phases followed by one reinstatement phase. The number of trails to reach the extinction criterion (no response within 45secs for 3 consecutive trials) and trail latency were recorded as was the number of trials to reach the reinstatement criterion (3 correct consecutive responses). Facial expressions during the first 5 trials of each extinction and reinstatement phase were also recorded as a marker of emotional response to expected reward not given and unexpected reward given respectively. The results of the study are presented and conclusions drawn as to consequence of altering the equine microbiome on equine sleep, emotional state and cognitive performance. References Appleton, J., 2018. The Gut-Brain Axis: Influence of Microbiota on Mood and Mental Health. Integr Med (Encinitas) 17, 28-32. Bulmer, L., 2020. High-starch diets increase behavioural reactivity, alter hindgut microbiota and brain neurochemistry in horses, School of Veterinary Medicine University of Glasgow. Greening, L., McBride, S., 2022. A Review of Equine Sleep: Implications for Equine Welfare. Front Vet Sci 9. McBride, S.D., Roberts, K., Hemmings, A.J., Ninomiya, S., Parker, M.O., 2022. The impulsive horse: Comparing genetic, physiological and behavioral indicators to those of human addiction. Physiol Behav 254, 113896.