Validation of a portable ultrasound machine for estimating sole thickness in dairy cattle in New Zealand

AIM: The aim of the study was to validate the use of a portable ultrasound machine for monitoring sole thickness by investigating the agreement between ultrasound and electronic calliper measurement of distance from the external to the internal sole surface (sole thickness) and the distance from the external sole surface to the distal phalanx (DP). METHODS: Distal limbs were collected post-mortem from 24 dairy cows. Measurements were made using a portable ultrasound machine (Mindray DP 6600) on both claws of the right hind and left front feet at the tip of the distal phalanx (site 1) and 25 mm towards the heel (site 2). DP and sole thickness were measured at each site. The limbs were then frozen and sectioned, and the same parameters measured using electronic callipers. The limits-of-agreement between the two methods were investigated, and receiver operator characteristic (ROC) analyses undertaken. RESULTS: Ultrasound images were obtained for 92 out of 96 claws. For sole thickness, as measured using callipers, the best correlation was with ultrasound-measured DP at site 1 (r=0.77). The mean difference between these two measures was 2.5 (SEM 0.15) mm and the range of the 95% limits-of-agreement was 4.2 mm. ROC analysis showed that a claw with an ultrasound-measured DP of <7.0 mm was >11 times more likely to have a sole thickness <5 mm than ≥5 mm, while a claw with an ultrasound-measured DP of >8.25 mm was 4.5 times more likely to have a sole thickness ≥5 mm than <5 mm. Soles could therefore be categorised as thin (DP <7 mm), marginal (DP 7–8.25 mm) or adequate (DP >8.25 mm) using this ultrasound machine. CONCLUSIONS: Examination of the claws of dairy cows using a basic portable ultrasound machine is sufficiently accurate for use in monitoring mean sole thickness in a group of animals. On an individual basis, measurement of DP can be used to categorise soles as thin, marginal or adequate. CLINICAL RELEVANCE: The measurement of DP using portable ultrasonography can be used to evaluate the role of sole thickness in clinical lameness outbreaks, and as a research tool to monitor the dynamics of claw parameters over time.