A sensitive microassay for the determination of hemolytic complement activity in bovine milk

A ⁵¹Cr release microhemolytic complement assay is described to detect hemolytic complement activity in bovine milk. ⁵¹Cr-labeled guinea-pig erythrocytes (GPRBC), which have been sensitized with a subagglutinating amount of rabbit anti-GPRBC, are placed in microtiter plates. Pooled bovine sera as source of complement to achieve about 50% of ⁵¹Cr release were added to each well prior to the addition of the samples on the test. Determination of CH100 titer was obtained by difference of counting between heated and unheated diluted whey samples from a standard linear regression. Comparative hemolytic values throughout lactation were established for the first time and confirmed the improved sensitivity of the assay.