Studies on the Acute Phase Reaction during Respiratory Infections in Calves

Gånheim, C. 2004. Studies on the acute phase reaction during respiratory infections in calves. Doctor ́s dissertation. ISSN 1401-6257, ISBN 91-576-6678-4 The overall aim of this thesis was to examine the acute phase response, as measured mainly by acute phase proteins (APP) and cellular response, in calves during different types of respiratory infection, and to identify potential markers useful in evaluation of their health status. Experimental infections were performed with virus, bovine virus diarrhoea virus (BVDV) or bacteria, Mannheimia haemolytica (M. haemolytica), or with a combination of the two micro-organisms. Special interest was focused on the differences between single BVDV or M. haemoytica inoculation and co-infection with both agents. In another study, calves were infected with the cattle lungworm, Dictyocaulus viviparus (D. viviparus) using different dose regimens. Finally, a study was performed to evaluate the usefulness of APP measurements as indicators of health in calf herds. Co-infection with BVDV and M. haemolytica induced the most severe clinical signs, while single M. haemolytica inoculation induced none or very mild clinical signs, while BVDV inoculation induced mild to moderate signs. Increases in the APP haptoglobin, serum amyloid A (SAA) and fibrinogen were observed after inoculations with BVDV and/or M. haemolytica. The increases coincided in time with the onset of clinical signs. The duration of elevated serum concentrations of SAA and fibrinogen was larger in the group inoculated with both BVDV and M. haemolytica. A marked decrease in lymphocyte numbers was observed after BVDV inoculation. This was mainly explained by a decrease in the numbers of CD4+, CD8+ and WC1+ lymphocytes. In contrast, M. haemolytica inoculation induced an increase in total neutrophil numbers, while the numbers of CD8+ and WC1+ lymphocytes decreased somewhat. The results indicate that detection of supra-normal APP levels could be useful to identify animals that are, or have recently been, clinically or subclinically diseased. Lungworm infection induced an increase in haptoglobin, SAA and fibrinogen, as well as in the numbers of eosinophils in blood. However, high numbers of eosinophils and low levels of APP do not exclude a diagnosis of lungworm. Thus lungworm infection may not be detected if measurements of APP are used to assess calf health. In a herd with high disease incidence, a larger proportion of calves had elevated serum concentrations of APP, and a larger number of days per calf with elevated levels of APP compared to a herd with low disease incidence. The results indicate that measurements of serum concentrations of APP can be useful as indicators of herd health.