Impact of cow-calf contact during the first week and following separation on cows' activity, behavior, feed-related parameters, and milk yield and composition.

Dairy farming systems are critically viewed by animal-welfare orientated consumers due to the rapid disruption of the maternal bond caused by immediate separation after birth. Cow-calf contact systems are therefore considered to be a more welfare-friendly alternative, offering varying contact durations and management strategies. One approach within cow-calf contact systems is the use of foster cows for calf rearing, typically introduced within or after the first week of a calf's life. However, separation after a cow-calf contact period may impact animals' behavior. This study examined the effects of cow-calf contact during the first week and following separation, focusing on cows' activity, lying behavior, feeding parameters, milk yield and their composition. The study was carried out at the TUM experimental farm Veitshof with 20 Brown Swiss cows distributed equally between an early-separation group (ESG) and a cow-calf contact group (CCC). In ESG, cows were separated directly (≤2 h) after birth, while in CCC they remained with their calves until d 8 in the morning after birth. Pedometers and neck collars were used to track activity, lying behavior, and feeding patterns. Milk yield and composition were also recorded for cows. Cows in ESG were reintegrated on d 8 after calving into the lactating herd after spending the same amount of time (d 1-7) in the calving area as cows in CCC. A mixed-effects model was used with group and time as fixed effects, and cow as a random effect. The results showed that cows in ESG exhibited lower daily activity impulses on d 8-10 compared with cows in CCC. In ESG, lying time declined from d 2-7 to d 8-10 as cows were reintegrated into the lactating herd. Cow-calf contact group exhibited a stronger drop in lying time after separation, reaching pre-separation values again on d 10. Feed intake time and rumination time were time-dependent, with ESG cows maintaining more stable rumination time values, while CCC cows exhibited a drop after separation and a peak in feed intake time on d 9. Milk yield was consistently higher in ESG, whereas CCC showed more pronounced temporal variation. In CCC, milk fat, lactose, and urea concentrations were lower during the early phase but increased toward the end of the study period. In contrast, milk composition in ESG remained largely stable, apart from generally higher milk pH, while SCC was higher in CCC on d 7. Overall, separation after one-week cow-calf contact triggered behavioral and performance related changes, with potential impairments on the energy balance, particularly due to higher activity and reduced rumination time.