Phylogenetic tree of a 245bp region of the 5′UTR. All field isolates are denoted by “Farm Number – PI Number”. * indicates isolates with equal 5′UTR nucleotide sequence identity to both BVDV 1a and 1j reference strains, + indicates isolates with 1% less 5′UTR nucleotide identity to BVDV 1j reference strains than to 1a reference strains, ^ indicates isolates with 1% higher 5′UTR identity to BVDV 1j reference strains than to either 1a or 1c reference strains, # indicates isolates with 1% less 5′UTR nucleotide identity to BVDV 1c reference strains than to 1a reference strains. Thirty six reference strains are included (underlined) each beginning with the genotype and sub-genotype to which they belong (1a-1m and 2) followed by their name; further details can be found in Table 3. Bootstrap figures supported by >70% of 1000 replicates are indicated.