Does ridden exercise influence tongue colour: A standardised photographic approach

Background: It has been suggested that “blue” tongues in photographic images represent abnormal/reduced blood circulation, but photographic representation of tongue colour has not been validated, so it is difficult to investigate relationships between colour alterations and potential predisposing factors.

Objective: To establish a standardised, reliable approach to recording tongue colour for use in investigation of potential welfare concerns.

Study design: Experimental.

Methods: An oral examination performed by a veterinary surgeon exposed the upper (UG) and lower gingiva (LG), and tongue (T). Lateral photographic images were obtained from nine horses immediately before and after a 20-minute standardised ridden (walk/trot/canter) exercise test. Horses were ridden using a bridle, snaffle bit, and noseband, with the nasal dorsum positioned vertically. A reference colour and exposure palette allowing for correction of images to a standardised white balance was included in the field of view. Images were standardised to the same exposure/white balance using the Red (R), Green (G) and Blue (B) measurement of white squares on the calibration palette. An outline around the UG, T, and LG on the left and right images was drawn and R, G, B content analysed using Colour-Histogram. Areas of dark pigmentation were avoided. Pre/post-exercise results were compared using a paired t-test (p < 0.05).

Results: For 25 paired left/right images there was no difference in mean R (214 ± 21 vs. 214 ± 16; p = 0.9), B (160 ± 26 vs. 160 ± 18; p = 1.0) or R:B ratio (1.36 ± .14 vs. 1.34 ± 0.1; p = 0.4) between sides after exercise. There was no significant difference in mean R, B or R:B ratio between pre- and post-exercise (p = 0.8, p = 0.5, p = 0.7, respectively).

Main limitations: Other physiological tests not performed.

Conclusion: In horses ridden in a bridle, snaffle bit, and noseband, no differences were found in tongue colour after exercise. Carefully standardised images of the tongue and gingival mucosa may offer a technique to investigate validated alterations in tongue colour balance under different conditions.