The objective of this study was to evaluate the influence of testicular disease on sperm morphology. The reproductive tracts of 33 dogs were evaluated clinically and with ultrasound, followed by orchiectomy and harvesting of fluid from the vas deferens to evaluate sperm morphology. A section from each testis was used to conduct histological analyses. Histological changes were noted in 71.2% of testes (47/66). Regardless of dog age, the most frequent pathology was testicular degeneration (80.8%; 38/47), whereas testicular tumors were observed only in adult and old dogs (25.9%; 7/27). Harvesting fluid from the vas deferens for sperm morphology assessment was effective in 87.9% of cases (58/66), and severe testicular degenerative processes induced an increase (P < 0.05) in the percentage of abnormal sperm when compared with normal testes or those with moderate testicular degeneration (special attention given to detached heads). In conclusion, regardless of dog age, breed or origin, a severe testicular degeneration process led to a significant increase in detached heads. Furthermore, the collection of sperm from the vas deferens proved to be an alternative and reliable technique for future research.