Contact with cows during the young age increases social competence and lowers the cardiac stress reaction in dairy calves

- Social behaviour and stress reactivity were compared in calves reared with cow-contact and calves reared with peer-contact only.
- Social Isolation and confrontation (with an adult cow) tests were conducted on 29 dairy farms in Switzerland and Germany.
- 'Cow-contact' calves show more adaptive social behaviour (submission during confrontation) than calves housed in peer groups.
- Calves reared with cow-contact show lowered cardiac response to isolation compared to calves reared with peer-contact only.
- The rearing system did not affect the behavioural and cortisol stress response.

Separating calf and cow within 24 h after birth is common practice in dairy farms. Some dairy farmers, however, practice a rearing system in which the calves are nursed by their dam or by foster cows. We investigated if dairy calves reared in such a system (calves with cow-contact) differ in their social behaviour and stress reactivity from calves reared without cow-contact (common rearing). Sixty-nine female calves (34 with cow-contact, 35 without cow-contact) between 27 and 93 days of age were subjected to a combined isolation-novel object-confrontation test. With the isolation-novel object test, we aimed to assess their stress reactivity and fearfulness towards a novel object. Following the isolation-novel object, we confronted the calves with an unfamiliar cow to assess if and how previous cow-contact has influenced their social behaviour. During the tests, behaviour was observed directly and the heart rate was recorded continuously; saliva samples for cortisol analysis were taken before and after the trial. The heart rate was higher in calves reared without cow-contact at the beginning of the trial, but was similar to the heart rate of calves reared with cow-contact at the end of the trial (F2,99 = 5.39, P = 0.006). We did not find an effect of cow-contact on saliva cortisol concentration or behaviour during the isolation-novel object test phase. In the confrontation phase, calves reared without cow-contact approached the unfamiliar cow more often than calves reared with cow-contact (F1,27 = 12.22, P = 0.002). Calves that were reared without cow-contact less often displayed a response to threatening behaviour of the cow compared with calves reared with cow-contact (F1,26 = 14.77, P < 0.001). In more detail, threatening behaviour of the cow caused calves reared with cow-contact to display submissive behaviour more often than calves reared without cow-contact (F1,26 = 16.94, P < 0.001). We conclude that rearing with cow-contact affected the cardiac stress reaction but not the hypothalamic-pituitary-adrenal axis reactivity, and led to a more adaptive social behaviour compared with traditional rearing without cow-contact.