Behavioural responses of dairy cows and calves to fenceline weaning after 4 or 6 months of full cow-calf contact

Cow-calf contact (CCC) systems, where cows and calves are housed together during all or part of the milk-feeding period, foster strong social bonds within dam-calf pairs. However, calves are still generally weaned and separated at younger ages than have been observed for semi-feral cattle. This study aimed to evaluate behavioural responses of dairy cows and calves to fenceline weaning after 4 or 6 months of full CCC. Additionally, the proportion of time spent by dam-calf pairs in close proximity (< 4 m indoors or < 8 m outdoors) prior to weaning was tested for its effect on behavioural responses. Dairy cows (n = 25) and their calves (n = 26) were housed in a freestall pen with free access to pasture for either 4 (4MO) or 6 months (6MO), after which calves were weaned outdoors via fenceline separation. Daily activity (lying time and step count) was recorded for all animals using accelerometers for 6 days before and for 11 days after weaning, while vocalisations and feed-seeking behaviour were collected for calves postweaning through direct observations. Scan sampling on 3 days during the end of the contact period was used to estimate proximity within each dam-calf pair, and calves were weighed regularly throughout the study. Calf feed-seeking behaviour and differences in lying time or step count (calculated as changes from a preweaning baseline value) for cows and calves were fitted with polynomial regression models. Directly after weaning, calves responded by decreasing their lying time, increasing their step count and vocalisations, and spending little time on feed-seeking; these responses were greater for 4MO calves. The calves, especially those weaned at 4 months, had reduced growth rates for several weeks postweaning, suggesting a lack of nutritional independence prior to weaning. Cow activity responses were similar but with no clear treatment differences in the first 3 days and with faster recovery times than for calves. Dam-calf proximity varied greatly between pairs but did not influence any of the modelled responses. Our results suggest that fenceline weaning causes behavioural responses indicative of distress in both calves and (to a lesser extent) cows, even when calves are weaned at a higher age.