A Postmortem Study on Ultrasonographic and Computed Tomographic Measurements of the Concavity of the Solar Surface in the Distal Phalanx of Cow Hindlimb Claws

New bone formations (NBFs) in the tuberculum flexorium of the distal phalanx (DP) are considered one of the etiological factors inducing claw horn disruption lesions, which frequently occur in the lateral claws of cow hindlimbs. The pathological bone changes in the DP are often not clearly visible using routine ultrasonography (US) of bovine claws. Thus, to enable an evaluation of these changes using US, this report investigated the utility of the angle in the concavity of the solar surface of the DP (referred to as the DP-SS angle), which varies with the severity of NBFs in the tuberculum flexorium. A total of 484 pairs of hindlimbs from 242 lactating Holstein cows collected at a slaughterhouse were examined using computed tomography (CT), and 274 hindlimb pairs from 137 animals were examined using both US and CT. For lateral claws, the DP-SS angle values showed a moderate to strong negative correlation with the NBF width (r = -0.71), while a weak correlation was found for the medial claws (r = -0.25). The DP-SS angles measured using US were significantly (<i>p</i> < 0.01) correlated with those measured using CT. Lateral claws with claw diseases had a significantly (<i>p</i> < 0.01) lower value (158.6°) than claws without claw diseases (161.6°). The value could not be measured using US for 51.4% and 30.0% of claws with double soles or a sole ulcer/sole crack, respectively, because the DP echotextures were unclear in the US. In the CT analyses, the DP-SS angle was the lowest in lateral claws with a sole ulcer/sole crack (154.4°); this value was significantly smaller (<i>p</i> < 0.01) than that of lateral claws with white line disease (162.3°) or a thin sole/thin sole toe ulcer (163.5°), as well as that of lateral claws without claw diseases (161.6°). In the US analyses, the value for lateral claws with a sole ulcer/sole crack (156.7°) tended to be slightly larger compared with the CT measurements, although it was significantly different from the value for claws without claw diseases (163.0°). The DP-SS angle is considered accurate for evaluating the degree of an NBF in the lateral claws of cow hindlimbs. The preliminary standard value of 160° was considered based on the CT analyses. However, the normal and abnormal thresholds of this value should be confirmed through the further field use of claw US because of the difference between the US and CT measurements. Additionally, creating disease-specific thresholds may be required owing to the considerable variation.