Serotypes of Pasteurella haemolytica in sheep in the midwestern United States.

Nasal secretions were collected from healthy lambs from flocks in Iowa and the surrounding states for 2 consecutive years. The 1st year, 322 lambs from 61 flocks yielded 202 Pasteurella haemolytica isolates, representing 9 established serotypes and 30 untypeable isolates. The 2nd year, 249 lambs from 49 flocks yielded 73 isolates, representing 9 established serotypes and 7 untypeable isolates. More isolates belonged to serotype 2 than to any other serotype. Serotypes 3, 4, and 10 (members of biotype T), were not isolated. Serotype 12 was also isolated and identified.