INTERPRETING THE BEHAVIOR OF CALVES IN AN OPEN-FIELD TEST - A FACTOR-ANALYSIS

The open-field test is commonly used but has been interpreted as indicating both fear in response to novelty, and locomotory motivation. To clarify the interpretation of the test, 16 female Holstein calves were tested alone in an open-field to determine how their behavioural and heart rate responses were affected by: (1) the novelty of the enclosure (5 and 15 weeks of age), (2) a period of previous exercise (7 and 14 weeks), (3) the presence of a familiar or unfamiliar person (8 weeks). Factor analysis revealed three weakly correlated factors. Factor 1 had positive loadings for sniffing and licking and a negative loading for immobility (SNIFF/LICK). Factor 2 had positive loadings for running and jumping (RUN/JUMP). Factor 3 had positive loadings for walking, defecating and vocalizing (WALK/VOCAL/DEFECATE). Scores for RUN/JUMP increased, and those for WALK/VOCAL/DEFECATE decreased with age. Prior exploration of the open-field decreased scores on SNIFlF/LICK and WALK/VOCAL/DEFECATE, but did not affect RUN/JUMP. When the test was repeated over 2 consecutive days, scores for RUN/JUMP were higher on Day 1 than on Day 2, but were not reduced by a preceding period of exercise on either day. Heart rate increased during the open-field test and the rise was correlated with RUN/JUMP. Basal heart rates decreased as the calves aged, but the heart rate response to the open-field was unaffected by age, prior exploration or prior exercise, Bouts of contact were shorter with an unknown person, but factor scores did not differ, Calves with high scores on WALK/VOCAL/DEFECATE made more contact with the person. Behaviour in the open-field reflects several motivations: sniffing and licking are primarily exploratory behaviours in response to the novel area; defecation and vocalization, associated with walking, may represent fearful responses to novelty and social separation; while running and jumping are elicited the first time the animals are allowed to run free in a large area, but may not represent endogenous sources of locomotory motivation.