Changes in physiological and immunological variables in weaned dairy calves exposed to different stressors

This study was conducted to investigate the effects of different stressors on physiological and innate immune variables in weaned dairy calves. Holstein steers (n = 40; 110 ± 11.8 kg body weight [BW]) were housed in individual pens in an environmentally controlled barn. Steers had <i>ad libitum</i> access to water and a starter ration. Steers were randomly allotted to four treatment groups (n = 10/treatment): (i) control (CON), (ii) transport (TRANS; transported in a livestock trailer for 4 h), (iii) lipopolysaccharide (LPS; administered i.v. 0.10 µg/kg BW), and (iv) vaccine (VAX; administered a <i>Mannheimia haemolytica</i> toxoid vaccine). One day prior to administration of stressors, indwelling jugular vein catheters and rectal temperature (RT) recording devices were placed in all steers. Whole blood was collected at -1, -0.5, 0, 1, 2, 3, and 4 h relative to administration of stressors for serum, plasma, and hematology. There was a treatment × time interaction (<i>P </i>≤ 0.01) for all hematology parameters except for hemoglobin and platelets. Monocyte, lymphocyte, neutrophil, and white blood cell concentrations were reduced (<i>P </i>≤ 0.02) in steers administered LPS compared to all other treatments. For steers administered the VAX treatment, white blood cell and neutrophil concentrations and the neutrophil: lymphocyte ratio increased (<i>P </i>≤ 0.04) 4 h post-treatment application compared to other treatments. There was a treatment × time interaction (<i>P </i>< 0.01) for RT where values increased in LPS and VAX steers at 1 and 4 h, respectively, while RT decreased in TRANS steers at 5 and 6 h. There was a treatment × time interaction (<i>P </i>< 0.01) for cortisol concentrations, where steers administered LPS produced the greatest increase in cortisol compared to all other treatments. There was a treatment × time interaction (<i>P </i>≤ 0.02) for all cytokines except for interleukin-13 (<i>P </i>= 0.12). Concentrations of these cytokines remained greater in LPS and VAX steers compare to CON and TRANS. These data demonstrate the differential immune responses to common challenges experienced by dairy calves.