Pituitary, adrenal, immune and performance responses of mature Holstein × Friesian bulls housed on slatted floors at various space allowances

The effect of various space allowances on the pituitary, adrenal and immune responses and on performance was investigated in 72 mature Holstein × Friesian beef bulls. The animals (weighing 403 ± 3.5 kg) were blocked by weight and randomly assigned to two groups (familiar, F, and unfamiliar, UF) × three treatments (1.2, 2.7 and 4.2 m2 per bull; n = 24 per space allowance), and housed for 83 days in 18 pens (n = 4 per pen). Blood samples were collected on days −1, 0, 3, 14, 36 and 77 with respect to mixing and housing on day 0. The bulls were given exogenous adrenocorticotrophic hormone (ACTH) on day 3 and corticotrophin-releasing hormone (CRH) on days 14, 36 and 77.Basal plasma cortisol concentration was not affected (P > 0.05) by mixing F and UF bulls. On day 3, basal cortisol was greater (P < 0.05) in bulls housed at 1.2 than those at 2.7 and 4.2 m2 space allowances while no effect was observed in ACTH-induced plasma cortisol concentration among treatments. Following CRH administration, there was no effect (P > 0.05) of treatment and treatment × time on plasma ACTH concentration. On day 14, interferon-γ production was lower (P < 0.05) in the bulls housed at 4.2 vs. 2.7 m2 and was intermediate but not significantly different (P > 0.05) for those housed at 1.2 m2. Animals housed at either space allowances had significant (P < 0.05) neutrophilia, lymphopenia, eosinopenia and decreased haemoglobin on day 3 compared with day 0. The liveweight gain from days 0 to 83 was lower (P < 0.05) in bulls housed at 1.2 compared with those at 2.7 and 4.2 m2. Housing bulls at 1.2 m2 space allowance had a detrimental effect on their growth and was associated with an acute rise in plasma cortisol concentration (on day 3) compared with those having space allowances of 2.7 and 4.2 m2/bull.