Salivary oxytocin response of dairy cows to nursing and permanent separation from their calves, and the influence of the cow-calf bond

Oxytocin is a hormone involved in milk let-down, facilitating maternal behavior and parent-young bonding, and attenuating the stress response under challenge, but the release of oxytocin also appears to be dependent upon the social context. Dairy cows are commonly separated from their calves at birth, preventing maternal behavior and the establishment of a social bond. The growing interest in maintaining cow-calf contact provides a practically relevant context to study how oxytocin is affected by differing levels of cow-calf contact. Furthermore, the oxytocinergic system is likely affected by the stress of permanent cow-calf separation, depending on weaning method and strength of the cow-calf bond. Dairy cows were managed with full-time (23 h/d of calf contact), part-time (10 h/d of calf contact) or no calf contact (separated 48 h after birth), and then weaned by either: 50 % reduction in original calf contact time in wk 8 and 9 (‘reduced-contact’), or calf contact time remained unchanged (‘unchanged-contact’). Permanent separation from their calves occurred at wk 10 (n=14 for each treatment combination). Saliva was sampled in wk 8 before and after a nursing event over 3d, and in wk 10 before and after permanent separation (2 h after, and every 24 h thereafter for 3d), and analysed for oxytocin concentration. Cow-calf bond was measured as: motivation for cows to reunite with their calves (pressure cows were willing to exert on a weighted gate), and frequency and duration of social interactions between dam and calf. Cows with the most opportunity for calf contact (full-time; unchanged-contact) tended to have higher oxytocin concentrations around nursing, and oxytocin concentration around nursing tended to be positively related to proportion of total daily time together spent in physical contact. Over the 4-d post separation period, oxytocin response was generally stable for cows with male calves, but the pattern was variable for cows with female calves and in opposing directions for full- and part-time cows. Reduced-contact cows had greater oxytocin concentration over the separation period than unchanged-contact cows, but only if they had a male calf. In unchanged-contact cows, the oxytocin response to separation tended to increase if the cow-calf bond was stronger. These results highlight the complexity of the oxytocin response to different social situations, which depended on prior level of calf contact, calf sex, and strength of the cow-calf bond. Future research should explore how management practices influence social bonds and the oxytocinergic system, given their role in modulating stress resilience.