How do group-housed dairy calves perceive the sickness of a companion?

Calves are social animals that establish strong bonds with their peers, showing affiliative behaviours and social interactions when housed together. However, changes in the group dynamics may occur when one individual becomes sick or is removed. This case study was retrospectively extracted from video recordings to investigate the behaviour of healthy calves and their interactions with a sick companion during her last day of life. Six female dairy calves, raised in 2 triplets from the first month of age, were moved into a group of six at 3.2±0.2 months old (mean±SD). All calves were monitored by the farm staff in line with EU regulation for the protection of calves and by the responsible veterinarian. The sick calf was repeatedly treated, and kept in the same pen to prevent isolation stress. All other calves were healthy throughout the full study. Calf behaviour was recorded by a video camera positioned on top of the pen for a welfare study. Data were gathered by a trained observer applying continuous recording at group level using BORIS software. The case study focused on the last 13 hours (5:00-18:00) before the farm personnel, who monitored the sick calf continuously, and the veterinarian separated her for humane end-of-life handling. At this time, which was 45 days after grouping into six, calves were 4.8±0.2 months old. The ethogram focused on behaviours towards and proximity to the sick calf performed by the healthy companions: grooming, sniffing, nudging/displacing, avoidance and other interaction; stand close and lie close. Descriptive statistical analysis was performed. Results showed that the sick calf lied in the pen centre during the whole observation time. Overall, 177 bouts of interactions were observed (125 behaviour and 52 proximity bouts) corresponding to 13.7% of the total observation time. The most frequent interactions were sniffing (46.9%) and stand close (27.7%), which were the only interactions performed by all 5 calves. Only one calf showed nudging/displacing (10 bouts) and only another one lied close to the sick companion (2 bouts, 75 minutes total). 18 bouts of grooming were observed. The majority of interactions were performed by two new companions (39% and 22% respectively), while the smallest number of interactions was performed by a calf of the original triplet (8.5%). Insights could support the hypotheses that calves can perceive sickness and upcoming loss, showing affiliative behaviours towards a sick companion even after a short time of living together, and especially if group-housed from an early age; but also, that calves may react in different ways, reflecting their individual personality, emotional status and bond with the companion. This case study was extracted retrospectively from observations of video recordings for an animal welfare project approved by the Ethical Committee of the University of Padua (OPBA).