ABSTRACT
The prevalence, distribution, and severity of caseous lymphadenitis (CLA) lesions in 4,089 mature culled sheep were determined from a sample obtained by random selection of animal lots from a total population of 37,383 animals presented at an abattoir. The animals originated from 5 geographic regions comprising 9 western states. The prevalence rate for all forms of CLA was 42.41%. The prevalence of CLA lesions was significantly different in animals originating from 2 regions than it was in animals from the other 3 regions. The results indicate that CLA is a disease affecting a considerable number of mature culled sheep in different regions of western United States. Lesion distribution was catalogued according to a 4-compartment system: thoracic lymph nodes, lung parenchyma, abdominal tissues, and skeletal tissues including peripheral lymphatic tissues. Prevalence rates were determined for lesions occurring in the thoracic viscera (24.97%), skeletal tissues (23.09%), and abdominal viscera (11.79%). The prevalences of thoracic CLA lesions were significantly different for animals originating from 2 regions than for animals originating from the 3 other regions. Severe or advanced lesions were observed in the thoracic (3.74%) and abdominal viscera (1.27%). Involvements of CLA in the thoracic cavity occurred as abscesses of lung parenchyma, thoracic lymph nodes, or both. The bronchial and mediastinal lymph nodes were the most frequently affected thoracic lymph nodes. The liver was the most frequently affected abdominal organ, with the kidney being the next most commonly affected. The gross and histopathologic characteristics of CLA abscesses and tissues adjacent to the lesions were described.
