Hematological Variables Are Influenced By Vaccine Antigen Type and Acute or Chronic Stress Model in Beef Calves

The objective was to determine the effect of replicating and non-replicating vaccine antigens administered to acutely or chronically stressed beef calves on hematologic and endocrine responses. A total of 48 crossbred beef steers (d 0 BW = 226 ± 6.2 kg) from a single ranch origin were used in a 2 × 2 factorial to evaluate main effects of stress, vaccine type and their interaction; resulting in 4 treatments (n=12/treatment) consisting of acute stress with killed virus vaccination (ACUKV), ACU with modified-live virus vaccination (ACUMLV), chronic stress with KV (CHRKV), and CHR with MLV (CHRMLV). The ACU treatments were weaned at their origin ranch on d -37 and transported 472 km to the study site near Canyon, TX on d -21 to allow acclimation. The CHR treatments were weaned on d -3, transported 460 km to a facility near Lubbock, TX on d -2, and relocated 164 km to the study site on d -1. Vaccine treatments were administered on d 0 and KV was revaccinated on d 14. Animal was experimental unit and dependent variables were analyzed using PROC MIXED with repeated measures (d). Hematological variables were determined from whole blood collected on d -2, 0, 1, 3, 5, 7, 14, and 21 via automated hemocytometer. Cortisol concentration was determined using ELISA from serum collected on d -2, 0, 1, 3, 5, and 7. Total leukocytes were not different on d -2 (P=0.66), but were lesser for CHR vs. ACU on d 0, 1, 3, 5, 7, 14 and 21 (P≤0.02). Vaccine type also affected total leukocytes; leukocytes were decreased for MLV on d 5, 7, and 14 (P≤0.04) compared to KV. Neutrophils (2.01 vs. 3.83 K/µL) and neutrophil:lymphocyte (0.27 vs. 0.67) were markedly increased (P<0.001) for CHR on d -2; conversely, neutrophils were decreased (P≤0.007) on d 1 and 21 for CHR. Monocytes were decreased on d 1, 5 and 7 for MLV (P≤0.04) and d -2 to 14 for CHR (P≤0.03). Eosinophils were reduced (P=0.007) for CHR (0.097) vs. ACU (0.176 K/µL) on d -2; however, a rebound response (P=0.03) was noted on d 0 such that eosinophils were 0.288 and 0.160 K/µL for CHR and ACU, respectively. Serum cortisol was greater (P≤0.04) for ACU on d -2 to 5, suggesting suppression of endocrine activity in CHR over time. Results indicate this CHR stress model and MLV vaccination may have more profoundly induced immunosuppression in beef calves.