Responses of weaned lambs to fear-eliciting situations: origin of individual differences.

The aims of this study were 1) to develop methods of objectively measuring fear in weaned lambs, and 2) to evaluate the effects of age, sex, breed, and rearing conditions on fear reactions. Four hundred forty-one lambs, aged 3 to 6 months, were submitted to three fear-eliciting situations (isolation, surprise effect, and human presence). Factor analysis revealed a first factor, interpreted in terms of fear, that accounted for 40% of total variance in the three tests. As in adult sheep, the main signs of fear were inhibition of feeding, long distance from the frightening stimulus, frequent immobilizations, and numerous high-pitch bleats. Behavior was also influenced by differences in general locomotor activity and exploratory motivation. Fear reactions were influenced by age (3- to 4-month-old lambs more fearful than 5- to 6-month-old), sex (females more fearful than males), breed (Romanov more fearful than Ile-de-France), and rearing conditions (artificial vs. maternal: almost no influence in males and influence in females depending on age). These results with sheep provide interesting theoretical and practical perspectives to the study of fearfulness. Copyright 2003 Wiley Periodicals, Inc. Dev Psychobiol 42: 131-147, 2003