A quantitative assessment of the risk of transmission of bovine spongiform encephalopathy by tallow-based calf milk-replacer.

A Monte Carlo simulation model was constructed to assess the risk of BSE transmission to calves by calf milk-replacer (CMR). We assumed that any BSE infectivity in the CMR would be associated with the allowable levels of impurities in tallow used to manufacture the milk-replacer. Simulations used three different levels of impurities, six different distributions of the BSE infectivity titers of CNS tissues and with and without inclusion of specified risk material (SRM). Our results suggest that tallow-based CMR could have been responsible for some BSE infections in nearly all simulations. The reduction in the allowable impurities in tallow and the exclusion of SRM have greatly reduced--but have not eliminated--the risk of BSE transmission by CMR The results of the simulations are associated with much uncertainty.