CLUSTERING OF FATAL FIBRINOUS PNEUMONIA (SHIPPING FEVER) IN FEEDLOT CALVES WITHIN TRANSPORT TRUCK AND FEEDLOT PEN GROUPS

Feedlot owners often state that shipping fever mortality does not affe ct calves in a random fashion across the feedlot; instead, mortality c an be abnormally high in certain truckloads of calves or in certain pe ns. However, these apparent ''clusters'' of disease might be no more t han coincidental concentrations of fatal shipping fever cases selected from a truly random distribution of cases throughout the feedlot. The purpose of this study was to distinguish between these two possibilit ies by critically examining the pattern of fatal shipping fever affect ing calves placed in a large beef feedlot. Management and mortality da ta from 36 339 spring-born calves entering a large commercial beef fee dlot in SW Alberta, Canada from 1985 to 1988 were used for the analysi s in this study. Once at the feedlot, calves were placed in pens of ap proximately 300 animals. Truck manifests (which include freight or car go documentation) and feedlot processing records were used to determin e the truck and auction market origin of all incoming calves. Because the prevalence of shipping fever mortality varied dramatically among y ears, an analysis was performed on each of the 4 years separately. To determine whether clustering occurred within the transport truck, test s of homogeneity of binomial samples were run on the truckloads of cal ves making up each individual pen. To determine whether clustering occ urred within a pen, a test for homogeneity of binomial samples was run within each year using the proportion of mortality due to fibrinous p neumonia in each pen; the intracluster correlation coefficient was use d to correct for the nested effect of truck within pen. When the incid ence of fatal shipping fever was high (greater than 2%), the disease c lustered within truckload groups of calves and also, one year, within pens. Further work is necessary to determine whether contagious or non -contagious factors are responsible for the clustering that was docume nted.