Acute phase proteins (APP) are used as markers of inflammation and sub-clinical disease and are considered potential biomarkers for pig health and welfare. However, reference ranges for their baseline concentrations are necessary before their use can be considered in routine herd health. In this study, C-reactive protein (CRP), haptoglobin (Hp), pig-major acute-phase protein (Pig-MAP) and transthyretin (TTR) baseline concentrations were determined in boars from a high health commercial herd and differences between seven commercial breeding lines within the herd were investigated. Reference ranges of 3.6-183 mg/L for CRP, 0.01-1.31 g/L for Hp, 0.32-2.9 g/L for Pig-MAP and 174-610 mg/L for TTR were found. Correlations were determined between Hp and CRP, Hp and Pig-MAP and CRP and Pig-MAP. Additionally, significant differences were found among the concentrations of CRP, Pig-MAP and TTR in seven commercial breeding lines.