The present study provides reference values of the caudal vena cava and aorta parameters in clinically healthy sheep with normal hydration status, to provide a guide to assess such large blood vessels, which will be helpful in diagnosing conditions that affect blood volume and, subsequently, theses large blood vessels. For this study, 30 clinically healthy sheep, with no observable clinical evidence of dehydration or cardiovascular disease, were identified for inclusion in the study. Using transabdominal ultrasonography, the measurements of both the diameter and area of caudal vena cava and aorta were evaluated using the paralumbar window view. The mean ± SD of the ultrasonographic measurements as well as the calculated indices for the caudal vena cava to aorta diameter and area ratios in the selected sheep were as follows 1.22 ± 0.11 mm for the diameter of caudal vena cava, 1.20 ± 0.11 mm for the diameter of aorta, 1.75 ± 0.15 mm2 for the area of caudal vena cava, 1.21 ± 0.11 mm2 for the area of aorta, 1.01 ± 0.02 mm for the index of the diameter of caudal vena cava to aorta, and 1.44 ± 0.05 mm2 for the index of the area of caudal vena cava to aorta. This is the initial study to provide reference values for the caudal vena cava and aorta parameters in clinically healthy sheep, informed by probability theory and statistical methodologies, the coefficient of variation, thereby demonstrating the precision of the assay. The ultrasound assessment of the caudal vena to aorta ratio is a promising method for early recognition of changes in vascular volume status in veterinary medicine. Thus, Knowing the reference values for the normal parameters of the large blood vessel parameters in clinically healthy small ruminants supports the future use of the caudal vena cava: aorta ratio as a novel index for assessing the hydration status in diseased sheep.