Elevated levels of beta-hydroxybutyric acid in periparturient cows and in vitro effect on respiratory burst activity of bovine neutrophils.

The in vitro effect of normal (0.01 to 1 mM) and subketotic (1 to 2.5 mM) doses of butyric acid on the respiratory burst activity of bovine polymorphonuclear leucocytes (PMNL) isolated from blood was studied by luminol-enhanced, PMA (phorbol-12-myristate-13-acetate)-induced chemiluminescence (CL). The subketotic concentrations of butyric acid induced a significant inhibitory effect on CL. In a cell free assay, consisting of sonicated cells and H2O2, no changes in activity could be observed. The activity of the myeloperoxidase was not significantly altered as shown by the ortho-dianisidine-oxidation assay. Also, the production of O(2)- measured by the cytochrome c reduction assay was not affected by different doses of butyric acid. Butyric acid had no scavenging effect on hypochlorite. The reason for the inhibitory effect on CL may be a decreased production of H2O2. Indeed, luminol-enhanced CL evaluates the production of H2O2. This could not be confirmed in the other assays mentioned above, because H2O2 was added externally in these assays. In conclusion, because of this inhibitory effect on the respiratory burst activity of PMNL, the elevated blood level of butyric acid after parturition in high yielding cows may be, in part, responsible for the higher susceptibility to local and systemic infections during the postpartum period and during subclinical and clinical ketosis.