Early social housing enhances positive behavioural opportunities in pre-weaned dairy calves

Pair housing benefits dairy calves; however, little is known about how housing type and the age at pairing influence the expression of positive and negative behaviours.
The aim of this study was to compare the behavioural dynamics of behaviours categorized as positive, maintenance or negative and to evaluate the total frequency of each behaviour across the pre-weaning period in calves pair-housed at 1 week of age, pair-housed at 4 weeks of age, or housed individually. Holstein female calves (n = 140) were assigned to one of three treatments: paired at 1 week (paired at 6–7 d; n = 48), paired at 4 weeks (paired at 29–30 d; n = 48), or individually housed (n = 44). Behavioural observations were conducted for 30 min after milk feeding (twice per day) from day 6 to day 50 using scan sampling. We used linear mixed-effects models to assess the effects of housing, age, and health status (diarrhoea and BRD) on calf behaviour.
Calves paired at 1 week displayed the most positive behavioural outcomes, showing higher expression of exploratory behaviour, play, and allogrooming, as well as lower expression of idleness, stereotypic behaviour, bedding intake, and non-nutritive oral behaviours compared with both calves paired at 4 weeks and individually housed calves. Pair housing at 1 week enhanced the expression of positive behaviours while reducing negative behaviours in pre-weaned dairy calves. Although pairing at 4 weeks led to some positive behaviour expression compared with individual housing, it was still insufficient to match the levels observed when calves were paired at 1 week of age.
These findings highlight the importance of not only providing social housing but also initiating pair housing early, as both the timing and the social context significantly shape calves’ behavioural trajectories and their ability to express positive welfare states.