Hematological and immunological responses to naturally occurring bovine respiratory disease in newly received beef calves in a commercial stocker farm.

ABSTRACT

The objective was to determine temporal changes in hematological and immune parameters in response to naturally occurring bovine respiratory disease (BRD) in commercially managed stocker calves. Forty newly weaned beef steers purchased from auction markets were housed at a commercial stocker operation in Crossville, TN. Blood samples, rectal temperature, and thoracic ultrasonography (TUS; 1 normal to 3 severe) were collected on days 0, 7, 14, and 21. Castration status (FC freshly castrated; PC previously castrated) was determined on arrival based on presence of a fresh castration site at the scrotum. Calves received antibiotics for BRD based on clinical severity scoring (CSS; 0 moribund, 4 moribund) and rectal temperature. Complete blood counts (CBC) were performed. Calves were categorized based on the number of treatments (NumTrt) received (0x, 1x, and 2x). Temporal variations in CBC and immune parameters were analyzed using mixed model repeated measure ANOVA (Proc GLIMMIX; SAS 9.4). Variation of CBCs and immune parameters based on TUS was determined using mixed model ANOVA. There was a NumTrt by day interaction effect on the responses of white blood cells (WBC) (P = 0.04) and haptoglobin (HPT) (P = 0.04). On day 21, WBC were greater in the 2x NumTrt group than other groups, but there were no differences in WBC between NumTrt levels on other days. Haptoglobin was greater in the 2x group on days 14 and 21 than 0x or 1x. Red blood cells (RBC) (P = 0.02) and WBC (P = 0.04) differed between FC and PC groups, and lower RBC and WBC were observed in the FC group. A castration status × day effect for mean corpuscular volume (MCV; P = 0.04) was observed where FC group had higher MCV at days 14 and 21 than the PC group. Tumor necrosis factor-α differed based on NumTrt (P = 0.03) and higher concentrations were found in 2x group. We observed a day effect for IL-1ß (P = 0.009) and TNF-α (P = 0.001). Significant effect of TUS on HPT at day 14 (P = 0.0004) and day 21 (P = 0.002) was observed. Combining HPT and platelet explained 15% of the variability in treatment status on a given day, whereas HPT and hemoglobin explained 10% of the variability in lung consolidation status. Although hematological and immunological parameters varied largely in our study, the potential of combining HPT with hematological variables should be studied further. Results from this study would help in understanding temporal changes in CBC and immune parameters in newly received stocker cattle.

Blood and immune parameters are altered during bovine respiratory disease (BRD) progression and can be used for predicting disease status. We aimed looking at the dynamics of hematology and immunology in newly received stocker cattle in naturally occurring BRD. Forty newly received stocker cattle were managed by a local producer and monitored for BRD occurrence for 21 d after receiving during the high-risk period. Newly weaned calves were monitored as they experience several stress factors and become prone to BRD. Additionally, there are limited data related to immunological changes that occur in high-risk stocker cattle. Since there is no perfect diagnostic test for BRD, the diagnosis of BRD is likely missed when only visual signs are used. We observed that haptoglobin (HPT) was the most important parameter to differentiate BRD severity. The combination of HPT with blood parameters (hemoglobin and platelets) was useful to predict treatment and lung infection status. Therefore, measuring hematological and immunological parameters might be helpful to determine BRD status and facilitate treatment decisions in newly received stocker cattle.