Comparison of methods for assessing the prevalence and extent of pneumonia in market weight swine

The purpose of this study was to compare four different techniques that may be used to assess the prevalence or severity of enzootic pneumonia in a swine herd. These techniques included: 1) assessing the percentage of lung involved and calculating a mean percentage and standard deviation for each herd, 2) counting the number of lungs in the herd sample that have greater than a predetermined amount of pneumonia and calculating the prevalence of the sample thus affected, 3) scoring only the lung from each herd sample that was maximally affected by pneumonia, and 4) allocating lungs to categories depending on the approximate extent of pneumonia. Five hundred and sixty pigs from 41 different swine herds in southern Minnesota were examined at slaughter and lungs were evaluated for the extent of pneumonia that was macroscopically visible.The mean percentage of pneumonia for a herd was positively and highly correlated with the standard deviation of that herd (r = +0.914; p < 0.0001), the prevalence of pigs having >/=5% lung involved with pneumonia in that herd (r = +0.946; p < 0.0001) and with the percentage of lung that was observed to be the maximally affected lung in each corresponding herd (r = +0.940; p < 0.001).The most informative procedure was assessing the percentage of lung involved and calculating a mean for the herd sample. Allocating lungs to categories based on approximate severity of pneumonia was less precise and more difficult to interpret. Assessing the prevalence of affected lungs, or evaluating the maximally affected lung was less time consuming and equally as informative for a herd-based indicator, as scoring the percentage of each lung and calculating a mean.