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

Separating calf and cow within 24h 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). Sixtynine 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 (F-2,F-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 (F-1,F-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 (F-1,F-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 (F-1,F-29 = 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. (C) 2016 Elsevier B.V. All rights reserved.