Abstract
This study was conducted to investigate the effects of different stressors on physiological and innate immune variables in weaned dairy calves. Dairy steers [n = 40;10 ±1.8 kg body weight (BW)] were transported to the Calf Building at the USDA-ARS Livestock Issues Research Unit where they were housed in individual pens in an environmentally controlled room. Calves had ad libitum access to water and a starter ration. At arrival, calves were randomly allotted to four treatment groups (n = 10/treatment): 1) Control, 2) Transport (transported in a livestock trailer for 4 h), 3) Lipopolysaccharide (LPS; administered i.v. 0.10 µg /kg BW), 4) Vaccine (administered a Mannheimia Haemolyticatoxoid vaccine; OneShot, Zoetis). One day before application of stressors, indwelling jugular vein catheters and rectal temperature (RT) recording devices were placed in all calves. Whole blood was collected at -1, -0.5, 0, 1, 2, 3, and 4 h relative to application of stressors for serum, plasma, and hematology. There was a treatment × time interaction (P ≤ 0.01) for all hematology parameters except for hemoglobin and platelets. Monocyte, lymphocyte, neutrophil, basophil, and white blood cell concentrations and the neutrophil:lymphocyte ratio were reduced (P < 0.02) in calves administered LPS compared with all other treatments. For calves administered the Vaccine treatment, white blood cell and neutrophil concentrations and the neutrophil:lymphocyte ratio increased (P < 0.04) 4 h post-challenge compared with other treatments. There was a treatment × time interaction (P < 0.01) for the change in RT relative to baseline values. The change in RT increased following administration of LPS and peaked at approximately 3 h post-challenge before decreasing to near baseline values. In contrast, RT began to increase 3 h post-challenge in calves administered the Vaccine treatment, where the greatest RT values were observed at 6 h post-challenge. There was a treatment x time interaction (P < 0.01) for cortisol concentrations, where calves administered LPS produced the greatest increase in cortisol compared with all other treatments. There was a treatment x time interaction (P < 0.01) for tumor necrosis factor-a (TNF-a) and macrophage inflammatory protein-1b (MIP-1b). Concentrations of TNF-a remained greater in LPS and Vaccine calves compared with Control and Transport calves while MIP-1b concentrations remained omcreased for calves administered LPS compared with the other treatments. Results from this study suggest that common challenges experienced by dairy calves differentially influence physiological and immunological variables in weaned dairy calves.