Effect of repeated regrouping and relocation on the physiological, immunological, and hematological variables and performance of steers

To investigate the effect of repeated regrouping and repenning (R&R) on the hypothalamic-pituitary-adrenal axis, immune function, blood biochemical and hematological variables, and ADG, 72 Holstein-Friesian (14-mo-old; 441 +/- 3.2 kg) steers were assigned to either the control (C; n = 30) or regrouped (R; n = 42) treatments and housed six per pen in 12 pens. The R steers were exposed to six R&R over 84 d. New pen cohorts were allowed to stabilize for 14 d, and none of the R steers was allowed to share the same pen or penmates where or with whom they were previously housed. Control steers were housed in the same pen with the same penmates. Steers were blood sampled 2 h before and 2 h after the first, third, and sixth R&R. Steers were weighed the day before each R&R. Median area under the plasma cortisol curve (AUC) was greater (P < 0.05) in R than C steers after the first R&R. Following the first, third, and sixth R&R, the median ACTH AUC did not differ between the treatments. Cortisol AUC in R steers decreased (P < 0.001) following the third and sixth compared with the first R&R, however, cortisol AUC in response to exogenous ACTH (following administration of dexamethasone at -12 h) after the third R&R was greater in C than R steers (P < 0.05). Corticotropin-releasing hormone-induced cortisol and ACTH AUC were not different in C vs. R after the sixth R&R. There were no differences among treatments in haptoglobin, fibrinogen, and concanavalin A-induced interferon-gamma after the first, third, and sixth R&R. Albumin, urea, and NEFA were greater (P < 0.05) in R than C steers after the first R&R. beta-Hydroxy-butyrate and glucose concentrations were greater (P < 0.05) in R than C, whereas no changes in the protein and globulin concentrations were found in C vs. R after the sixth R& R. White blood cell, differential and total count, red blood cell, and platelet numbers did not differ in C vs. R after the first and third R&R. Lymphocyte numbers and mean corpuscular volume were greater (P < 0.05) in R than C steers after the sixth R&R. Monocyte numbers were greater (P < 0.05) in R than C steers following first R&R. There was no difference in the overall ADG in C vs. R; however, there was a tendency (P = 0.10) for lesser ADG by R than C steers following second R& R. In conclusion, steers exposed to R&R responded with increased plasma cortisol, albumin, urea, and NEFA. Repeated R&R did not have a sustained detrimental effect on immune and production measurements.