Use of computer snout morphometry in atrophic rhinitis monitoring

ATROPHIC rhinitis (AR) is a serious disease of pigs worldwide, causing growth retardation and respiratory problems. The severity of AR is estimated by examination of the conchae for atrophy after slaughter. Checks for AR at slaughter are usually performed by examining a transverse section of the snout. Optimal results are obtained if the cut is placed between the first and second premolars (Martineau-Doize and others 1990). As many pigs as possible should be examined; however, between 20 and 30 animals per batch has been suggested as an acceptable sample by Goodwin (1988). Several methods of scoring AR have been used (Bendixen 1971, Straw and others 1983, Backstrom and others 1985). These methods are based on a visual assessment of the snout structures, which is subjective. As well as wide variations between these systems, there is also a considerable observed variation within each method. Results from different slaughter tests should be compared with caution, as demonstrated by D'Allaire and others (1988). It is recommended that the same experienced observer, using the same scoring system, should perform such comparisons. The varying severity of the atrophic changes has led to the development of a quantitative assessment method. Collins and others (1989) first used morphometry with the aid of a digitising tablet linked to a microcomputer and software provided by the manufacturer of the digitiser. Those authors used a turbinate perimeter ratio, based on measuring the cross-sectional area of the nostril and turbinates within the area of the conchae. The turbinate area ratio (TAR) morphometric method, first described by Done (1984), is based on measuring the cross-sectional area of free space (free air space) within the area of the conchae. This method was modified by Gatlin (1996) and does not include the dorsal turbinate in the measurements. This morphometric …