P. multocida is a Gram-negative capsulated bacterium that is the causative agent of a wide range of animal diseases, including bovine haemorrhagic septicaemia, atrophic rhinitis in pigs and fowl cholera, a serious disease of poultry which can present in both acute and chronic forms. The increasing consumer demand for free-range and organic poultry has resulted in an increased incidence of fowl cholera. P. multocida strains are currently classified into 16 Heddleston serovars using the gel diffusion precipitin test with antisera raised against somatic or lipopolysaccharide (LPS) antigen. P. multocida LPS is both a protective immunogen and an important virulence factor. We have developed a multiplex PCR typing system to replace the Heddleston serotyping scheme and have shown that the 16 Heddleston type strains can be grouped into 8 genotypes based on their LPS outer core biosynthesis genes. The most common strains isolated from Australian poultry belong to Heddleston serovars 3 and 4. Here we report that the type strains of these two serovars produce related but distinct LPS structures and share a common LPS outer core biosynthesis locus, L3. We also show using TargeTron® mutagenesis of genes within this locus, that truncation of the LPS outer core structure can be attributed to mutations within one of the six encoded glycosyltransferases. Interestingly, LPS structural analyses of over 35 field isolates belonging to genotype L3 reveal that a further four related, but distinct, LPS structures/glycoforms are produced by field isolates belonging to L3, and in some field isolates multiple LPS glycoforms are simultaneously produced. The existence of these multiple LPS glycoform-producing strains in the field raises significant questions about the efficacy of P. multocida vaccine strains that elaborate only a single LPS structure.