Reduction of Mycobacterium avium ssp. paratuberculosis in colostrum: Development and validation of 2 methods, one based on curdling and one based on centrifugation.

The aim of this study was to develop and validate 2 protocols (for use on-farm and at a central location) for the reduction of Mycobacterium avium ssp. paratuberculosis (MAP) in colostrum while preserving beneficial immunoglobulins (IgG). The on-farm protocol was based on curdling of the colostrum, where the IgG remain in the whey and the MAP bacteria are trapped in the curd. First, the colostrum was diluted with water (2 volumes colostrum to 1 volume water) and 2% rennet was added. After incubation (1 h at 32°C), the curd was cut and incubated again, after which whey and curd were separated using a cheesecloth. The curd was removed and milk powder was added to the whey. Approximately 1 log reduction in MAP counts was achieved. A reduction in total proteins and IgG was observed due to initial dilution of the colostrum. After curd formation, more than 95% of the immunoglobulins remained in the whey fraction. The semi-industrial protocol was based on centrifugation, which causes MAP to precipitate, while the IgG remain in the supernatant. This protocol was first developed in the laboratory. The colostrum was diluted with skimmed colostrum (2 volumes colostrum to 1 volume skimmed colostrum), then skimmed and centrifuged (at 15,600 × g for 30 min at room temperature). We observed on average 1.5 log reduction in the MAP counts and a limited reduction in proteins and IgG in the supernatant. To obtain a semi-industrial protocol, dairy pilot appliances were evaluated and the following changes were applied to the protocol: after 2:1 dilution as above, the colostrum was skimmed and subsequently clarified, after which the cream was heat treated and added to the supernatant. To investigate the effect of the colostrum treatment on the nutritional value and palatability of the colostrum and the IgG transfer, an animal experiment was conducted with 24 calves. Six received the dam's colostrum, 6 were given untreated purchased colostrum (control), and 2 groups of 6 calves received colostrum treated according to both of the above-mentioned methods. No significant differences were found between the test groups and the dam's colostrum group in terms of animal health, IgG uptake in the blood serum, milk, or forage uptake. Two protocols to reduce MAP in colostrum (for use on-farm or at a central location) were developed. Both methods preserve the vital IgG.