Effects of individual versus pair housing during the first 15 d on pre-weaning growth performance and hair cortisol concentrations in dairy calves

In modern dairy production systems, calves are separated from their dams shortly after birth and are commonly housed individually, limiting social interactions with peers. Although this management practice aims to reduce the transmission of infectious diseases and to prevent cross-suckling, it may also lead to social isolation. This study investigated the effects of early-life individual versus pair housing of female calves during the first 15 d of the milk-feeding period on pre-weaning growth performance and hair cortisol concentrations (HCCs). A total of 31 Holstein female calves were initially allocated to individual housing ( n =19) or pair housing ( n =12; six pairs). Of these, 20 calves completed the 85 d follow-up and constituted the primary analysis population (individual housing, n =11; pair housing, n =9). Calves were housed in zeolite-bedded calf pens for the first 15 d after birth. From day 16 onwards, calves were transferred to a group pen equipped with an automatic milk-feeding robot and remained there until the end of the study (day 85). Body weight (BW) was recorded at birth and at predefined time points, and HCC was measured at birth and on day 85 in a randomly selected subset of 14 calves (7 per treatment). Housing treatment had no significant effect on BW or HCC ( P >0.05), whereas the treatment × time interaction was significant for average daily gain (ADG; P <0.05). Sensitivity analyses incorporating all available BW and ADG observations supported the primary growth performance findings. However, these findings should be interpreted cautiously because of the small sample size and the difference in space allowance per calf. This study adds evidence regarding individual versus pair housing, limited to the first 15 d before transfer to group housing, showing significantly higher ADG during days 15–30 in calves initially housed individually but no statistical support for the main effects on pre-weaning BW or HCC.