Two Gram-stain-negative, facultatively anaerobic bacteria, designated ZY170218(T)and ZY180512, were isolated from lungs of dead sheep with hemorrhagic pneumonia in Yunnan Province, China and their taxonomic positions were studied by a polyphasic approach. The two isolates grew optimally at 37 degrees C, pH 9.0 and 1.0% NaCl (w/v), and showed identical 16S rRNA, recN and rpoB gene sequences. Phylogenetic analysis based on 16S rRNA gene sequence showed that the two strains fell within the cluster of species in the genusMannheimiaand formed a separated lineage with comparatively low similarity to the closest related speciesM. granulomatis(96.5%). Phylogenetic analysis based onrpoBgene indicated that the strains formed a monophyletic evolutionary lineage, with low sequence similarity <= 89.0% to the species of the genusMannheimia. The genomic OrthoANI values between strain ZY170218(T)andM. granulomatisandM. haemolyticawere 80.4% and 83.1%, respectively. The genomic G + C content of strain ZY170218(T)was 39.1 mol%. The predominant fatty acids (> 5%) of the two strains were C-16:0, C-14:0, C-18:1 omega 7c, summed feature 3 (C-16:1 omega 7c and/ or C-16:1 omega 6c) and summed feature 2 (C(14:0)3OH/ C(16:1)Iso). The major polar lipids of strain ZY170218(T)were phosphatidylglycerol, phosphatidylcholine, monogalactosyldiacylglycerol, bis(monoacylglycero)phosphate and diacylglycerols. The sole respiratory quinone of the two strains was CoQ-7. On the basis of phylogenetic, phenotypic and chemotaxonomic features, strain ZY170218(T)and ZY180512 clearly represents a novel species of the genusMannheimia, for which the nameMannheimia ovissp. nov. is proposed. The type strain is ZY170218(T)(= CGMCC 1.13620( T) = KCTC 15731( T)).