LABORATORY EXAMINATION OF SUSPECT TUBERCULOUS LESIONS DETECTED ON ABATTOIR POSTMORTEM EXAMINATION OF CATTLE FROM NONREACTOR HERDS

In each of the years 1994, 1995 and 1996 approximately 3,000 suspect t uberculous lymph nodes were detected on abattoir post mortem examinati on of cattle from clear herds and were submitted for laboratory examin ation. Sixty six per cent of the lesions (6701 ex 9186) were diagnosed as tuberculous. The majority of diagnosis (8515; 92.7%) were based on histopathological examination, while in 671 cases (7.3%) the histopat hological findings were inconclusive and a diagnosis was reached on th e results of culture. The most common non-tuberculous lesions were clu b-forming granulomas (actinobacillosis/actinomycosis), parasitic granu lomas, Rhodococcus equi granulomas and neoplasms. More tuberculous les ions were detected in cows than in steers and heifers. In over 90% of affected animals the tuberculous lesions were in the retropharyngeal o r the bronchial/mediastinal lymph nodes. There was a significant diffe rence in the distribution of lesions between cows and younger stock, w ith steers and heifers having a higher proportion of tuberculous lesio ns in retropharyngeal lymph nodes and a lower proportion of tuberculou s lesions in bronchial/mediastinal lymph nodes then cows.