Retrospective evaluation of semen quality in bulls in Spain, managed in extensive grazing systems over a 10-year period.

Extensively managed beef herds often lack systematic reproductive monitoring, which can lead to reduced fertility rates and economic losses. Bull Breeding Soundness Evaluation (BBSE) is a critical tool for identifying sires with suboptimal reproductive performance. This study aimed to assess semen quality and reproductive soundness in beef bulls raised under extensive systems, to determine the prevalence of unsatisfactory breeders and identify factors affecting reproductive performance. A retrospective analysis was conducted on 1541 evaluations for breeding soundness in 549 bulls (checked in different years or re-checked after an unsatisfactory result) across 45 farms in southern Spain between 2014 and 2024. Bulls underwent physical examination, scrotal circumference (SC) measurement, and semen collection (by electroejaculation). Sperm motility was assessed using computer-assisted analysis. Bulls were classified as suitable, questionable or unsatisfactory based on BBSE criteria. Overall, 83.1 % of bulls passed BBSE: 68.9 % were classified as suitable and 14.2 % as questionable. A total of 16.9 % were unsatisfactory due to low progressive motility, anatomical defects, or clinical conditions. Morphological sperm assessment was not performed in all the samples. A total of 230 bulls classified as unsatisfactory in a first evaluation were reevaluated (63.5 %), showing that 52.9 % of them exhibited acceptable semen quality later, highlighting the importance of follow-up testing. Limousin bulls had the highest probability of passing BBSE (82.5 %), while older bulls (>85 months) had reduced odds. Seminal parameters varied significantly among breeds, and age affected SC but not sperm motility or other semen parameters. BBSE is an essential tool in extensive systems to ensure optimal bull fertility and prevent economic losses. Repeated evaluations improve accuracy, particularly for bulls initially deemed unsatisfactory. Breed, age, and farm management practices significantly influence reproductive outcomes and should be considered in breeding programs.