Effect of Coxiella burnetii infection on milk constituents and cow behaviour

Context. The role of Coxiella burnetii in intramammary infection (IMI) in dairy cows is not fully understood. Aims. The objective of this study was to investigate changes in milk constituents and behaviour such as daily activity (arbitrary unit/day) and daily rumination (min/day) in cows exposed to C. burnetii. Methods. In total, 1029 quarter milk samples were manually collected from 48 cows before and after alveolar milk ejection in the automatic milking rotary at the University of Sydney's dairy farm. Each milk sample was analysed for the following parameters: immunoglobulin G (cIgG) against C. burnetii via ELISA, somatic cell count (SCC), total immunoglobulin G (tIgG), lactate dehydrogenase (LDH), serum albumin (SA), milk protein%, milk fat%, and subjected to microbiological culture. The daily activity and daily rumination changes were recorded using heat- and rumination long-distance tags across 21 days before detection of IMI (n = 42 cows). Linear and logistic mixed models were used, with 'cow' and 'quarter nested within cow' as random effects. Results. The presence of cIgG was quarter-specific; the cIgG+ quarters (n = 64) had significantly greater tIgG (P < 0.001), LDH (P < 0.001), SA (P < 0.001) and milk protein% (P = 0.002) than did cIgG- quarters (n = 279). The cIgG+ quarters had significantly greater SCC, tIgG, LDH and SA responses than did controls (P < 0.05), but lower responses than did Gram-negative coliform IMI (P < 0.05). Gram-positive IMI caused by coagulase positive/negative Staphylococcus, Streptococcus uberis, Streptococcus dysgalactiae, Corynebacterium spp. in cIgG+ quarters resulted in greater tIgG, LDH and SA responses than in control quarters (P < 0.05). Coagulase-positive Staphylococcus IMI was associated with the presence of cIgG as assessed by Fisher's exact test (P < 0.05). The cIgG+ group had a significant (P < 0.05) reduction in daily rumination compared with the cIgG- group in the study period. Conclusions and implications. The cIgG antibody responses are quarter specific with greater tIgG, LDH, SA and milk protein in the affected quarters, as well as behavioural changes in the cow, and therefore might be useful for detection of C. burnetii IMI.