Comparative histological studies of mechanically versus manually processed sheep intestines used to make natural sausage casings

The natural sausage casings industry is large and worldwide, and casings prepared from the small intestine of sheep form a large part of it. Food safety authorities in several countries have been concerned about the risk to consumers from the bovine spongiform encephalopathy (BSE) agent. Although this agent could enter the European small ruminant population via infected feed, there is no evidence that it has. Because the BSE agent introduced experimentally into sheep and goats has a tissue distribution very similar to that found in animals with natural cases of scrapie, the agent would likely be found in the intestine and lymph nodes of some infected sheep from an early age. When natural casings are prepared from the intestine, the ileum (known to be infected in animals with natural cases of scrapie) is removed and the intestine is cleaned such that the inner (tunica mucosa) and outer (tunica serosa and tunica muscularis) layers are removed, leaving only the submucosa. There are two main methods for cleaning the intestine: manual and mechanical. The cleaning efficiency of these two methods was examined in the commercial environment as practiced on healthy sheep considered fit for human consumption in Turkey and Great Britain. The investigation involved a qualitative and quantitative histological approach. There was no significant difference in cleaning efficiency between the two methods, although there was some variation. No Peyer's patches or residues of them were found in any part of the cleaned casings. This finding is important because in sheep infected with transmissible spongiform encephalopathies (TSEs) Peyer's patches are likely to contain a major part of the intestinal infectivity. No serosa was found in any casing, but some residual mucosa and muscularis was retained, with more of the former than the latter. The results indicate that the cleaning efficiency of the two methods was broadly equivalent, that there was significant removal of tissue that could promote TSE infection, and that TSE risk reduction likely would be achieved by both methods, although this probability could not be quantified by the methods used in this study.