Middle ear infection in feedlot lambs

Of 133 feedlot lambs that died and were necropsied, 67 had normal lungs and 66 had pneumonic lungs. The middle ears of all lambs were opened by a specified technique. Of the 67, 8 (12%) had otitis media, and of the 66, 26 (39%) had otitis media. The difference in prevalence in the 2 groups was highly significant (P less than 0.005). In acute stages, the mucosae of tympanic cavities and tympanic membranes were inflamed and the cavities contained fluid, whereas in later stages lumens were partially filled with exudate. In chronic stages, however, exudate remained in lumens and mucosae were thick and rough. None of the tympanic membranes was ruptured, and none of the external acoustic meatuses contained exudate. The infected ears of 24 lambs were cultured and Pasteurella haemolytica was isolated from 18, and P multocida from 3. The infections probably ascended from the pharynx through the auditive tubes into the tympanic cavities.