SURVIVAL OF MYCOBACTERIUM-PARATUBERCULOSIS AND PRESERVATION OF IMMUNOGLOBULIN-G IN BOVINE COLOSTRUM UNDER EXPERIMENTAL CONDITIONS SIMULATING PASTEURIZATION

Objective-To determine whether Mycobacterium paratuberculosis could su rvive in colostrum after pasteurization. Additionally, this study inve stigated the effect pasteurization had on IgG concentration in colostr um. Animals-Colostrum samples were collected from cattle (beef and dai ry) owned by the state of Ohio. Procedure-Colostrum was divided into a liquots and inoculated with variable concentrations of M paratuberculo sis (ATCC No. 19698: 10(4), 10(3), and 10(2) colony-forming units/ml). Half the samples at each concentration were subjected to pasteurizati on temperatures (63 C) for 30 minutes and the remainder were kept at a pproximately 20 to 23 C. All samples were incubated (Herrold's egg yol k medium with and without mycobactin J) and observed for growth during the next 16 weeks. Additionally, the IgG concentration of colostrum w as determined by radioimmunoassay before and after pasteurization. Sam ples that coagulated at pasteurization temperatures were mechanically resuspended before measurement of IgG concentration. Results-Growth of M paratuberculosis was retarded but not eliminated by pasteurization. Growth was observed in all unpasteurized samples incubated on Herrold 's egg yolk medium with mycobactin J but in only 2 of 18 pasteurized s amples similarly cultured. Growth from pasteurized samples appeared 5 to 9 weeks after growth was observed from nonpasteurized samples. Mean colostral IgG concentration was 44.4 g/L in nonpasteurized samples an d 37.2 g/L in pasteurized samples, a decrease of 12.3%. High-quality c olostrum (> 48 g of IgG/L) had a significantly greater loss of IgG con centration than did colostrum of lesser quality (P = 0.002). Conclusio ns-Pasteurization lessened, but did not eliminate, growth of M paratub erculosis from experimentally inoculated colostrum samples. Pasteuriza tion resulted in a significant decrease in colostral IgG concentration but not to an unmanageable level that would preclude the colostrum's use for passive transfer of immunity. Clinical Relevance-Colostrum is macrophage rich and may serve as a source of M paratuberculosis infect ion to calves. Pasteurization of colostrum may lessen the risk of infe ction, but will not totally eliminate M paratuberculosis.