PSII-7 - Is scrotal ultrasound a useful tool in ram breeding soundness examination?

Abstract: Varicocele, a condition of abnormally dilated veins within the pampiniform plexus, is associated with reduced male fertility in several species but its frequency and impact in rams is not well documented. Semen was collected and pampiniform plexus ultrasound performed in early December during breeding soundness examinations (BSE) of mature Composite-IV rams over a three year study. A portion of rams were evaluated in multiple years and data from a total of 129 collections on 90 rams were available for analyses. Semen parameters were estimated by computer-assisted sperm analysis (CASA). Imaging software was used to quantify the cross-sectional area of five vessels per testis and average areas of the left testis (AAL), right testis (AAR), and both testes (AAT) were calculated. The correlation between AAL and AAR measured on the same ram within a year was moderate and positive (0.51; P < 0.001). However, correlations between AAL, AAR, and AAT measured on the same ram in consecutive years were not different from zero. Average vessel area was analyzed with fixed effects of testis side (AAL or AAR), year (2020, 2021, or 2022), ram age (2, 3, or ≥ 4 yr-old) and a random effect of ram. Across years, AAL was 23 to 25% greater than AAR and 16 to 18% greater in ≥ 4-yr-old than younger rams (P < 0.01). Unilateral varicocele (UV) was diagnosed when a ram’s AAL/AAR or AAR/AAL ratio exceeded 1.5 and, for rams sampled in multiple years, those diagnosed in one year were considered affected for all subsequent years. Within year, prevalence of UV ranged from 16 to 36%. Scrotal circumference (SC) and CASA parameters were analyzed with fixed effects of year, ram age, and UV status and a random effect of ram. Within 2- and 3-yr-olds, sperm from UV rams had lower motility than unaffected rams (42.1 ± 6.7% vs 62.2 ± 4.1% and 47.8 ± 7.4% vs 70.1 ± 4.7%, respectively; P ≤ 0.02) but no differences were observed within 4-yr-old rams. Across ages, sperm from UV rams had slightly lower percentage normal than unaffected rams (91.5 ± 1.1% vs 94.3 ± 0.74%; P = 0.03). Sperm concentration, progressive motility, and SC were unaffected by UV status. Future studies will evaluate the effect UV status on siring capacity. Ultrasound methodologies previously refined to diagnose varicocele in boars helped identify sub-fertile rams that would not have been classified by routine BSE procedures. However, these methodologies would benefit from concurrent machine learning and software development to ensure imaging consistency across technicians and streamline procedures for real-time decision making. USDA is an equal opportunity provider and employer.