Effect of within-group heterogeneity of nutritional requirements and of competition for food on intake and feeding behaviour in Charolais cows

24 dry (D) and 12 lactating (L) Charolais cows took part in 3 trials combining two factors: within-batch heterogeneity of nutritional requirements (D and L, either mixed or not mixed within the batches) and the competition level for food (1 trough per cow vs 1 trough per 2 cows). In trial A (6 D, 6 L), the within-batch heterogeneity was tested without competition for food. In trial B1, the competition for food was tested on 2 homogeneous batches made of 6 D cows. In trial B2, the competition for food was tested on 2 heterogeneous batches (3 D + 3 L cows). The cows received hay ad libitum. The social rank, the intake level and the parameters of the feeding behavior were assessed individually. Heterogeneity and competition for food disrupted the feeding pattern. Competition for food caused desynchronisation of the feeding activity. In all cases, the energy balance remained largely positive. The L cows had the most stable feeding behaviour because of their high motivation to eat. The D cows displayed more variable adaptation to feeding. With competition for food, D cows reduced their intake when in homogeneous groups (with the dominated cows greatly decreasing their feeding time), and increased their intake when associated with L cows, the social rank having no effect. In conclusion, the level of nutritional requirements is the major factor, before the social status, guiding the adaptive mechanisms of the feeding behaviour of the cows.