ASSOCIATION BETWEEN CEREAL CONTENTS IN THE DIET AND INCIDENCE OF NECROTIC ENTERITIS IN BROILER-CHICKENS IN NORWAY

The quarterly cumulative incidence of necrotic enteritis in the broile r chicken population of south-eastern Norway varied between zero and 3 4.8% during the years 1969-1989. Two epidemics appeared during the stu dy period. The first and second epidemics lasted approximately 5 and 2 years and had peak incidences of 34.8% and 25.3%, respectively. The m edian incidence of all quarters was 1.2%, reflecting the generally low incidence during non-epidemic quarters. Univariable regression analys is indicated that necrotic enteritis occurred more often during the mo nths October-March than during the months April-September. The inclusi on levels of maize, barley, oats and wheat in broiler starter feed var ied between zero and 38.0%, zero and 20.0%, zero and 26.0%, and 6.0% a nd 38.6%, respectively. A single primary feed variable was specified, based on a ratio comprising weighted values of maize, barley and wheat . This variable showed a striking covariation with disease incidence, but tended to increase and decrease a few quarters earlier than the di sease incidence. Analyses of the associations between disease incidenc e and each of the cereal grains maize, wheat and barley, as well as th e association between incidence and the primary variable comprising th e latter three cereal types, were performed. Season and dietary animal proteins modified the associations between disease incidence and each of the feed variables. At above-median levels of animal proteins, sig nificant associations were restricted to the primary variable, barley and maize, during the cold season. At below-median levels of animal pr oteins, the primary variable, barley and wheat, was associated with di sease incidence. Above-median levels of maize protected against necrot ic enteritis, whereas barley and wheat were risk factors.