Thyroid ultrasound as a new tool to assess thyroid metabolism in cattle: preliminary results

Thyroid troubles are poorly documented in cattle. Ultrasonography is a tool used in other species to evaluate thyroid pathologies. The objective of this work is to describe the normal ultrasonographic appearance of the thyroid gland in cattle and to validate the reliability of its measurements.
In this study, 11 calves and 12 adult cows were enrolled at the University Veterinary Clinic of Liege. A thyroid ultrasonography was realized on each animals using a linear (calves) or convex (cow) probe on two views (transverse and longitudinal), measuring the length (l), width (w) and height (h) of each lobe and the height of the isthmus. Finally, the animals were euthanized and their thyroids were removed for weighing, measuring and histological examination. Volume was measured by liquid displacement, and calculated using two formulas: PI/6*l*w*h; PI/4*l*w*h.
The appearance of the thyroid was iso- or hyperechoic to the muscles and homogeneous. The capsule also appeared hyperechoic. Then, although the thyroid measurements are mostly significantly different (p>0.05) from those in post-mortem, the volume measured did not differ significantly (p>0.1) from the volume calculated. Ultrasound did not detect histological abnormalities such as follicular hypo- or hyperplasia. In one cow, a follicular cyst 0.4 cm in diameter was observed.
Further studies are needed to validate the ultrasound examination on a larger number of non-debilitated animals. Intra or inter-observer variability could be measured, for example. Additional work is also needed to address other aspects of thyroid metabolism, such as the use of ultrasound Doppler and hormonal blood tests.