Elevation of bovine serum C-reactive protein and serum amyloid P component levels by lactation.

C-reactive protein (CRP) and serum amyloid P component (SAP), which are known to increase in sera from humans and many other animals with acute inflammation caused by infection, toxic drug administration or injury, were previously purified from bovine serum. These serum levels were determined by enzyme-linked immunosorbent assay (ELISA) using specific antiserum to bovine CRP or SAP which was prepared by immunizing rabbits and goats with each purified protein. Among 68 healthy Holstein cows, 45 non-lactating cows had levels of CRP and SAP of 20.6 +/- 1.4 and 27.6 +/- 1.3 micrograms/ml respectively; 23 lactating cows had higher levels of CRP and SAP (76.0 +/- 13.6 and 38.3 +/- 5.5 micrograms/ml respectively). In the latter group, there was a high correlation between milk yield and serum CRP levels (P less than 0.001). From these observations, it was assumed that lactation might stimulate CRP synthesis rather than SAP synthesis in bovine liver as an acute phase reaction, and that CRP might be called a lactation-associated protein.