Dose dependency and individual variability in selected clinical, haematological and blood biochemical responses after systemic lipopolysaccharide challenge in cattle

Previous studies have noted that susceptibility to systemic lipopolysaccharide (LPS) exposure seems to differ between individual cows. However, to date inter-individual variation in the response to intravenous injection of LPS has been reported only as an empirical finding, and its existence or extent has never been backed up by statistical analyses. The aim of the present study was therefore to investigate the dose-dependency of clinical, haematological and blood biochemical responses to intravenous LPS injection in dairy cattle and to determine the extent to which these responses differed between individual cows. Eight dairy cows each received three intravenous injections of Escherichia coli LPS (10, 100, and 1000 ng/kg, consecutively) at three-week intervals. All three LPS doses induced clinical, haematological, and blood biochemical responses lasting up to several days. The strength of all of the responses increased significantly with an increasing LPS dose. A statistically significant inter-individual variation was demonstrated for all clinical, haematological, and blood biochemical responses except for serum calcium concentrations. More than half of the statistical variation in white blood cell and thrombocyte counts could be attributed to the individual. The results of this study show that despite the existence of a dose-response relationship between LPS and ensuing clinical, haematological, and blood biochemical responses, the majority of responses to LPS differ significantly in strength and duration from cow to cow.