Frequency and consequence of caseous lymphadenitis in sheep and lambs slaughtered at a Western Australian abattoir

A total of 8,711 sheep in 3 distinct age/sex groups were examined to determine for occurrence and extent of caseous lymphadenitis after slaughter at a major Western Australian abattoir. An adaptation of current mean inspection procedures to provide a numerical weighted evaluation according to number, site, and size of lesions was used to determine extent of involvement. Frequency in slaughter populations was estimated to be 3.4 +/- 0.6% for lambs, 41.8 +/- 3.9% for mixed-age rams, and 53.7 +/- 1.5% for adult ewes at 95% confidence intervals. The results confirmed that frequency increased with age, but also revealed increases in extent of involvement and occurrence of visceral lesions, particularly in association with lesions of the body. Nevertheless, lesions occurred more frequently in the body than in the viscera. However, the mean visceral involvement was greater than mean body involvement in all groups, and the ratio was found to be more or less constant. Visceral involvement was found to be more extensive in rams than in ewes. Difficulties associated with complexity of current inspection procedures were also recorded. The relevance of these findings to pathogenesis and postmortem disposition after slaughter is discussed. It is suggested that current postmortem inspection criteria should be reevaluated.