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Association between acute phase proteins and clinical signs of respiratory disease in dairy calves
Kaura, R., Dorbek-Kolin, E., Loch...
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Objectives
Bovine respiratory disease (BRD) is a leading cause of morbidity, mortality, and antimicrobial consumption of pre-weaned dairy calves. Assessment of clinical BRD symptoms in field conditions impedes making inferences on the presence of infection and inflammation and thus sets subjective criteria for antimicrobial treatment. The acute phase response (APR) is a part of host innate immunity and the first response to infections and tissue damage, which causes significant concentration revision in acute phase proteins (APPs), e.g., haptoglobin (Hp), serum amyloid A (SAA), and fibrinogen (Fib), in the blood. APPs have poor diagnostic specificity but are considered very sensitive in detecting clinical or subclinical inflammation or infection. So far, there is limited information available about which of the respiratory disease signs better predicts the infection and inflammation of the respiratory tract.
Therefore, this study aimed to identify the possible associations between different APPs with clinical signs of respiratory disease in dairy calves under field conditions and to assess their potential as a diagnostic tool complementing current BRD diagnosis.
Materials and Methods
Sixteen large Estonian commercial dairy farms with >400 dairy cows were included in this study. At each farm, five clinically healthy calves and five calves with clinical BRD signs in the age range of one to ten weeks were selected. The following clinical parameters were measured in each calf: rectal temperature (°C; 0 = < 39.0, 1 = 39.0–39.49, 2 = ≥39.5), respiratory rate (breaths/min; 0 = <45, 1 = ≥45), nasal discharge (0 = no, 1 = yes), cough (0 = no cough, 1 = yes), and demeanor (0 = normal, 1 = depressed). Blood samples from the jugular vein of each calf were collected in EDTA tubes for Fib measurement and in serum tubes for SAA and Hp measurements. From one farm, six healthy calves were included, making for an overall sample size of 161 calves for SAA and Hp estimation. Fib measurements were performed from blood samples from 11 farms, making for an overall sample size of 110 calves. Serum Hp concentration was determined using an ad hoc hemoglobin-binding assay. Serum SAA concentration was measured with a commercially available ELISA kit. Plasma Fib concentration was measured using the heat precipitation method. Linear mixed-effect regression analysis with farm as random intercept was used to study the associations between the recorded clinical signs and concentrations of APPs; separate models were built for the three outcome variables Hp, SAA, and Fib. The final models were produced by backward elimination of the variables from the original models. Age was controlled in the statistical models, except for Hp, to avoid a possible confounding effect. Pearson’s correlation analysis was used to identify the relationships between APPs. The modelling and the diagnostics were performed using Stata/IC 14.2. Results were interpreted as significant if p < 0.05.
Results
Clinical signs that were observed in calves were diarrhea (62.1%), increased rectal temperature (≥39.5°C; 36.0%), increased respiratory rate (29.2%), nasal discharge (16.8%), cough (14.3%) and depressed demeanor (5.0%). Serum SAA concentration was positively associated with increased rectal temperature of ≥39.5°C. Hp levels was positively associated with increased rectal temperature of ≥39.5°C and presence of nasal discharge. In case of Fib concentration, positive associations were found with increased rectal temperature of ≥39.5°C, increased respiratory rate of ≥45 breaths/ min, and calves exhibiting cough.
Fib showed a moderate positive correlation with Hp (correlation coefficient = 0.46) and SAA (correlation coefficient = 0.42) concentrations, whereas between Hp and SAA a weak positive correlation (correlation coefficient = 0.32) was found.
Conclusions
This study found association between serum APP concentrations and clinical signs of respiratory disease in dairy calves. Increased rectal temperature (≥39.5°C) best represented the inflammation during respiratory disease measured through elevated APPs. Calf-side tests for Fib measurement could serve as valuable diagnostic tool to make inferences about the presence of systemic inflammation and to assess underlying tissue damage, thus aiding in treatment decisions.
Acknowledgements
Authors are grateful to all the farms and their staff that participated in the study. This work was financed by the Estonian Research Council grant (PSG268).
Keywords: Acute phase proteins, respiratory disease, dairy calves.
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