Strong associations among rumen endotoxin and acute phase proteins with plasma minerals in lactating cows fed graded amounts of concentrate.

The objective of this investigation was to determine associations among rumen endotoxin, plasma serum amyloid A (SAA), and C-reactive protein (CRP) with plasma Ca, Fe, Zn, and Cu in lactating cows challenged with graded amounts of rolled barley grain in the diet (i.e., 0, 15, 30, and 45% of DMI). Correlative relationships among variables were determined by linear and nonlinear regression procedures adjusted for the effects of day, animal, and experimental period. Increasing the amount of grain in the diet was successful in inducing an acute phase response, as assessed by augmentation of rumen endotoxin and plasma CRP and SAA (P < 0.01). The correlative analysis revealed inverse, nonlinear relationships of rumen endotoxin and plasma SAA with circulating Ca. Interestingly, plasma Ca reached the asymptotic plateau at 10.6 mg/dL. The increase in rumen endotoxin was associated with an abrupt decrease in plasma Fe (R(2) = 0.91; P < 0.001). A similar relationship, although at a reduced estimation accuracy (R(2) = 0.21; P < 0.01), was observed between rumen endotoxin and plasma Zn. Augmentation of rumen endotoxin and plasma CRP resulted in a positive, biphasic response of plasma Cu. In conclusion, the increase in rumen endotoxin in response to high-grain diets, and the resulting increases in plasma SAA and CRP, were strongly correlated with fluctuations of plasma minerals. Results suggest that new feeding strategies should be developed to curb the release of endotoxin in the rumen fluid to prevent perturbing minerals in the plasma.