Behavioural reactivity of heifer calves in potentially alarming test situations: a multivariate and correlational analysis

The aim of the present study was to determine the degree of consistency of individual differences in behavioural responses of heifer calves over time and across different situations. Twenty-five Holstein Friesian heifer calves were individually subjected to the same set of four behavioural tests at 3, 16 and 29 weeks of age. The tests involved measuring the calves' responses to a stationary human, a novel object, an open field (novel environment), and to tethering restraint. Principal component analysis (PCA) of measures recorded at each age was used to identify independent dimensions underlying the calves' reactivity to these situations. The consistency of individual differences was established by ranking the behavioural scores and the scores of factors extracted by PCA and then estimating the correlations between the ranks of each individual calf at each of the test ages. At each age, PCA revealed four factors that could be labelled: "locomotion", "vocalisation", "interaction with a novel object", and "interaction with a human". Individual differences in 7 of 13 behavioural measures and in scores of all factors except "interaction with a human" were consistent between 16 and 29 weeks of age. Rank orders for scores of the factor labelled "interaction with a novel object" were significantly correlated across all three ages. Our results support the existence in calves of stable characteristics mediating reactivity to challenge. Multiple behavioural dimensions obtained with PCA suggest that behavioural responsiveness of calves to challenge is governed by a number of underlying factors rather than univariate phenomena, such as fearfulness or coping style. (C) 2003 Elsevier B.V. All rights reserved.