Testicular volume measurements obtained with ultrasound images and its association with total sperm count in ejaculates from stallions

Abstract

Testicular volume is usually related to sperm production capacity. A non-invasive method for assessing testicular measurements has been using ultrasound images, which allows a detailed analysis of the testicular parenchyma and isolate it from the surrounding structures. This study aimed to evaluate the most effective method for measuring testicular volume using ultrasound images and compare it to the total number of sperm per ejaculation, over a year. This was done by either measuring the width of each testicle to get the total testicular width (TTW; cm), or by determining the height, width, and length of both testes to calculate total testicular volume (TTV; cm³). Eight light-breed stallions were followed-up for one-year, testicular measurements using ultrasound were carried out every 15 days, prior to semen collection from each stallion. Semen, without the gel fraction, was evaluated immediately after collection to estimate the total sperm count in the ejaculate (x10⁹). The seasons of the year (summer, autumn, winter and spring) were considered to track the values throughout the year; differences between the means were compared using Tukey's test. Associations between variables were computed using the Pearson correlation method. Results are presented as mean ± standard error of the mean (SEM), and statistical significance was established at P<0.05. Testicular volume varied throughout the year for both TTW and TTV (respectively presented; P<0.0.05), with higher values observed in summer (9.39 ± 0.11; 179.30 ± 4.08), and spring (9.15 ± 0.07; 172.30 ± 2.38), lower values in autumn (8.92 ± 0.09; 166.18 ± 3.83), and winter (8.48 ± 0.09; 156.57 ± 2.79). A moderated correlation was observed between TTW and TTV (R=0.51; p<0.05). For total sperm count in the ejaculate, both summer and spring showed higher values (6.03 ± 0.36 and 6.51 ± 0.34, respectively) compared to autumn and winter (5.00 ± 0.04 and 4.86 ± 0.36, respectively). A moderated correlation was observed between total sperm count in the ejaculate and either TTW (R = 0.6; P>0.05) or TTV (R = 0.54; P>0.05). Testicular dimensions are typically measured using calipers to determine total scrotal width or via ultrasound to calculate TTV. Ultrasound has the advantage of assessing only the testicular parenchyma, whereas caliper measurements also include surrounding structures. However, positioning the ultrasound probe to accurately measure testicular length requires more technical skill due to the positioning of the stallion's testicles within the scrotum. Therefore, obtaining TTW through ultrasound is a valuable tool for assessing testicular volume in stallions.