Physiological challenges facing newly-calved heifers include parturition, adaptation to a concentrate-rich diet and a negative energy balance caused by the demands of lactation and continued growth. In addition, animals are subject to considerable psychological stress caused by new surroundings, social interactions with new herdmates and increased human contact. Abnormal behaviour, including prolonged time spent standing and reduced eating and rumination activity, may result from these combined challenges and contributes to further problems. The objective of this study was to assess the effect of housing early-lactation heifers solely with other heifers or in a mixed-parity group on the quantity and timing of eating, ruminating, lying, standing and stall use.