Influence of group size on behavioural and immune responses of buffalo young bulls

From November 2009 to February 2010, twenty-one buffalo bulls were used to evaluate the effect of group size on behavioural and immune responses. Fourteen bulls (group HS) were group-housed in an indoor slatted floor pen with an outdoor paddock (3.2+3.2 m2/animal). Other 7 (group LS) were group-housed in a similar pen having the same space allowance per animal. The animals at beginning of experiment were aged 455±72 d and weighed 337±67 kg. Animals were subjected to seven sessions of instantaneous scan sampling at ~15-d intervals. Observations were made every 10 min over a 5-h period (1000 to 1500 h). Behavioural variables were expressed as proportions of subjects observed in each category of posture and activity. In addition, rapid behaviours such as agonistic, social, and reproductive interactions, social licking, and self-grooming were recorded continuously. These variables were expressed as number of interactions per animal per hour. Phytohaemagglutinin (PHA, 1 mg/animal; intradermal injection) was used to assess in vivo cellular immunity, whereas 5 mg of keyhole limpet hemocyanin were injected subcutaneously to evaluate antibody response. The immune responses of group HS were assessed only on seven animals chosen at random. Behavioural data were analysed with a two-way ANOVA (group size and period of observation). In vivo cellular immunity response was subjected to ANOVA with one factor (group size). Antibody response data were analysed using a linear mixed model for repeated measures. When more animals were involved in eating activity an higher number of aggressive interactions were observed compared to the period away from feeding (0.96 vs 0.56; SE 0.13). Immune responses were not affected by group size. It can be concluded that group size had not a detrimental effect on buffalo bull welfare.