Case-control study on the risks of BSE infections in Northern Germany.

This study was to identify risk factors for bovine spongiform encephalopathy (BSE) by means of individual case-control data. 43 BSE cases in a defined region in Lower Saxony and Schleswig-Holstein were compared with 84 control animals. Purchase of new breeding stock and cross contamination between feed on the farm did not seem to have influence on the BSE incidence in these regions. The results indicate independent risk patterns. Pattern 1: Cows with high milk yield seemed to be at risk on big farms with adjacent pig production and when they were not fed milk replacer. Pattern 2: Milk replacer (esp. from certain producers) is a risk factor for Non-Red Holstein cattle, low yielding cows and farms without pig production. Pattern 3: Red Holstein cattle not being fed milk replacer have a higher BSE risk than other breeds when they have a low milk yield and live on small farms with pig production. This study, like findings in Bavaria, Lower Saxony and Schleswig-Holstein, strengthens the hypothesis that BSE in Germany was caused by a feed mediated ubiquitous exposure to PrPsc during a confined time period. Producers, in need of buying animal derived feed components during that time slot, were more likely to spread the PrPsc than others. Their increased risk is not necessarily due to an inadequate purchasing policy, but can also be coincidental. The breed Red Holstein is not the risk factor itself but represents the risk from concentrated feed for animals during a susceptible age period (calves), Therefore, the authors suggest a continuous exclusion of animal-derived fat components from milk replacers.