Repeatable individual differences in behaviour and physiology in juvenile horses from an early age

Abstract Most people living or working in close association with animals are familiar with individual differences in their behaviour, and awareness is growing that understanding such differences can contribute to improved management, production and welfare. Nevertheless, due to the considerable logistic and financial difficulties of conducting longitudinal studies, particularly in the large, slow-growing mammalian species comprising an important part of the world’s domestic animals, there is still little information on how early such differences emerge and whether they persist across different developmental stages. In an extension of a previous study of the behavioural and physiological (heart rate variability, HRV) response of 30 Azteca-breed foals of both sexes to repeated brief maternal separation from birth to weaning, we tested the same animals post-weaning in two tests of brief separation from their social group when they were approximately nine months and one year old, and recording the same behavioural and physiological variables as previously. As in the earlier study, we found stable individual differences in several behavioural variables: vocalization rate (R = 0.54, P