Technical note: Comparison between two tracing methods with ultrasonography to determine lumen area of the caudal artery in beef cattle.

Two experiments were conducted to compare variation between 2 tracing methods in measuring cross-sectional lumen area of the caudal artery in 5 beef heifers on 3 different dates (Exp. 1) and to compare tracing methods in detecting changes in artery lumen area after 5 heifers were switched from a diet containing nonendophyte-infected tall fescue [Schedonorus arundinaceus (Schreb.) Dumort] seed to one containing endophyte-infected tall fescue seed (Exp. 2). Lumen area determined by tracing the Doppler flow signal was 25% less than that determined by tracing the intima of the connective tissue, but there was no difference (P = 0.90) in the variation of measures between the 2 methods in Exp. 1. Declines in lumen area were detected at the same level of significance (P < 0.01) for both tracing methods after cattle in Exp. 2 were switched from noninfected to infected tall fescue diets. Variation in lumen areas was different between noninfected and infected diets with tracing the Doppler flow signal (P < 0.05) or the intima of the connective tissue (P < 0.01). Results indicated that lumen area of the caudal artery can be measured with similar precision by tracing the intima of the connective tissue in the artery wall or the outer boundary of the Doppler flow signal.