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 < 0.05). In contrast, S calves exhibited increased tongue-rolling behaviour than group-housed calves (P < 0.05). However, there was no significant HR difference among the treatments, except for G12 calves at 15 days of age, which yielded the highest HR (118.13 ± 10.73 times/min; P < 0.05) level. Levels of saliva secretory immunoglobulin A (SIgA) were highest in G12 calves (28.69 ± 1.58 ng/mL), which first decreased and then considerably increased as the S calves (27.41 ± 1.09, 20.60 ± 1.36, and 26.79 ± 1.31 ng/mL; P < 0.05) increased in age. Concentrations of serum IL-2, IL-6, and TNT-α in the group-housed calves were higher than those in the S group (P < 0.05). Body weight (BW) in G12 calves was lower than that of other groups (57.25 ± 1.50 kg; P < 0.05). S calves displayed lower voluntary solid feed intake (VFI) and higher body length (BL) than grouped calves (2.02 ± 0.20 kg, 84.32 ± 0.83 cm; P < 0.05). The withers height (WH) was higher in S and G3 calves than G6 and G12 calves at 46 days of age (90.23 ± 2.21, 89.65 ± 2.18 cm vs 87.88 ± 1.59, 87.25 ± 1.53 cm; P < 0.05). Taken together, our study suggests that before weaning, group-housed calves exhibit more natural behaviours, higher levels of immunity, and solid feed intake than solitary calves.