Effects of group size on the behaviour, heart rate, immunity, and growth of Holstein dairy calves

Abstract This study investigated the effect of group size on the behaviour, heart rate, immunity, and growth of Holstein calves. A total of 132 calves were randomly assigned to 1 of 4 treatments from birth to 46 days of age. These included single housed (S) or group housed with three (G3), six (G6), or twelve calves (G12) with six replicates for each. Behavioural responses were observed at 15, 30, and 45 days of age, and then physiological activities, including heart rate (HR) and saliva secretory immunoglobulin A (SIgA) levels, were measured. The serum immune indices of interleukin-2 (IL-2), interleukin-6 (IL-6), tumour necrosis factor-α (TNF-α), and growth were measured at 16, 31, and 46 days of age. Group-housed calves exhibited significantly increased self-grooming, allogrooming, locomotive play, social play, exploration, standing, and walking behaviours and decreased lying behaviour (P