Evaluation of measures taken by ultrasonography and caliper to estimate testicular volume and predict daily sperm output in the stallion.

The semen of 26 stallions, 2-20 years of age, was collected once a day for 7 consecutive days to determine daily sperm output (DSO). After the last collection, 17 stallions were castrated. Testicular volume was estimated using two methods. Length, width, height, of each testis were measured by caliper. Length, width, height, cross-sectional area and circumference at the widest point of the testis were measured by ultrasonography. Both caliper and ultrasound measurements were first made in the live animal, and again in vitro. There were no differences in these measurements because of method or condition of the animal, i.e., whether the measures were taken in the live animal or after castration. The volume of an ellipsoid (4/3 pi abc, a = height/2, b = width/2, c = length/2) is introduced as a method of accurately estimating testicular volume (r = 0.99) as well as predicting DSO (r = 0.92) in the stallion. The authors of this report suggest that this estimation can be performed by substituting values derived by ultrasonography or calipers.