Horned and dehorned dairy cows differ in the pattern of agonistic interactions investigated under different space allowances

Limited space in dairy cattle farming is associated with frequent encounters between cows, often resulting in agonistic interactions and injuries, especially in horned cows. Previous studies with dairy cows investigated space allowances in the waiting area in front of the parlour, the lying area, and the outdoor exercise area with respect to social behaviour. However, direct comparisons between horned and dehorned cows are lacking. In the present study, we compared social behaviour, locomotor activity, and heart rate variability of horned and dehorned dairy cows at four space allowances of the outdoor exercise area (5, 8, 12, 15 m2 per cow) for 1 h on 4 consecutive days. The study involved 12 farms, six with horned and six with dehorned cows. On each farm, 20 cows were used, of which six (two of high, medium, and low rank each) were selected as focal animals. Results showed that the total number of agonistic interactions decreased with increasing space allowance for both horned and dehorned cows. Agonistic interactions were highest in cows of high rank and lowest in cows of low rank, irrespective of horn status. The proportion of agonistic behaviour without body contact was higher in horned than in dehorned cows and increased with increasing space allowance. The proportion of head butts resulting in avoidance behaviour of the receiver (successful head butts) was higher in horned than in dehorned cows and was lowest at the smallest space allowance, irrespective of horn status. Locomotor activity was highest at the beginning of the experimental hour, irrespective of horn status and rank, but on a higher level for low-ranking cows compared with medium- and high-ranking cows. Results of the heart rate variables were inconclusive. The RMSSD (root mean square of successive differences of interbeat intervals) generally increased with increasing locomotor activity and was slightly higher in high- and medium-ranking cows compared with low-ranking cows. The RMSSD/SDNN ratio (SDNN: standard deviation of all interbeat intervals) decreased in all rank categories with an increase in locomotor activity and was on a slightly higher level in high-ranking than in medium- and low-ranking cows. In conclusion, irrespective of space allowance, horned cows did not show more agonistic behaviour than dehorned cows. However, horned cows displayed a different pattern of agonistic interactions as dehorned cows showing more interactions without body contact. To mitigate agonistic interactions, horned and dehorned cows would benefit from enlarged space allowances