Sub-clinical necrotic enteritis (NE) is a major economic cost to the broiler production industry due to poor growth and feed conversion efficiency of broiler chicken flocks, higher condemnation of livers or rarely the whole carcasses at the slaughter house and an increased risk of microbial contamination of poultry meat. Sub-clinical NE is a multifactorial disease although Clostridium perfringens plays a major role in its pathogenesis. Its diagnosis and confirmation are quite different from those of general infectious diseases. Disease confirmation is from the presence of necrotic or ulcerative lesions on the small intestinal mucosa with identifiable aggregates of pathogenic C. perfringens. C. perfringens numbers in the small intestinal digesta or the mucosal scrapings are not correlated with disease severity, whereas counts above 106 cfu/g in the caecal contents indicate an increased probability of NE-specific gut lesions. Not only does the presence and counts of C. perfringens strains capable of producing related toxins affect the incidence of the disease but also a number of predisposing factors are important in the aetiology of NE. The major factors that predispose growing chickens to sub-clinical NE are diet variables, diseases that cause mucosal damage of the intestine and environmental factors that either alter the development of gut associated lymphoid tissue or change litter quality within the production house. Dietary variables may be a major cause of variation in sub-clinical NE in commercial broiler production; differences in polysaccharides, lipids, protein sources, protein digestibility and the presence of antinutritive factors have been identified as variables affecting the incidence of the disease.

The question of which cut-off point would be more appropriate in the selection of sub-clinical obsessive-compulsive (OC) samples is an important methodological issue that has not been formally addressed, hence prompting the current study. Three groups of sub-clinical OC subjects, scoring 1, 1.5, and 2 standard deviations (SD) above the mean on the Padua Inventory, and a matched non-OC control group, were compared on various clinical and personality measures. As expected, the three sub-clinical groups had higher scores than the non-OC group on measures of OC symptoms (including obsessional slowness), depression, anxiety, and on personality measures of neuroticism, psychoticism, and obsessional traits. However, no significant differences were observed between the three sub-clinical groups on most measures, although the 2 SD group had higher scores on neuroticism and obsessional personality traits. It is concluded that a wide range of selection criteria can yield similar results that are interpretable within the current theoretical models of Obsessive-Compulsive Disorder (OCD). It is suggested that subjects with a diagnosis of OCD should be carefully excluded from sub-clinical studies. [A Spanish abstract follows the references.]