A comparative study of different methods of orchidometry in a canine model

An investigation was carried out to compare the testicular volumes obtained by different methods of assessment in a series of dogs.

After obtaining ethical approval for the study, ten dogs were identified which were scheduled for castration, either at the owner's request or prior to being placed in suitable homes. A Prader orchidometer, which consists of a series of ovoid model testes inscribed with corresponding equivalent volumes, was used as an indirect method of assessing the volume of each testis. Percutaneous measurements of length and width of each testis were also carried out prior to surgery under general anaesthesia, using both a sliding and a pinch type caliper. After each testis was removed it was isolated and submerged in a beaker containing water in order to get a direct estimate of its volume by fluid displacement. Using the formula for deriving the volume of an ellipsoid from length and weight measurements, the volumes derived from the caliper measurements were estimated and compared with the orchidometer and fluid displacement values. Pearson correlation coefficients were calculated to obtain the correlations between the values produced by the four methods.

The Prader orchidometer and the pinch type caliper both showed significant correlations, of 0.64 and 0.62 respectively, with the definitive values obtained by fluid displacement. The correlation obtained with the sliding caliper (0.4) was not significant. Despite the significant correlations, all the indirect methods consistently overestimated the real volumes obtained by fluid displacement.

Estimates of testicular volumes obtained by orchidometer and pinch type caliper are useful for situations where a qualitative rather than quantitative assessment of testicular volume is required.