Changes in bull usage and semen importation patterns: A 5-year national-scale analysis in a subtropical dairy system

This study examined national patterns in Taiwan's frozen dairy cattle semen imports from 2020 to 2024 using official import clearance records issued by the Bureau of Animal and Plant Health Inspection and Quarantine. A total of 643 individual Holstein sires were identified across all shipments during the 5-yr period. Annual import volumes, semen type distributions, and sire-specific usage patterns were analyzed to characterize changes in breeding strategies. Genetic indices for imported sires were obtained from the Council on Dairy Cattle Breeding August 2025 evaluation and linked with import data to assess how sire characteristics corresponded to importer preferences. Descriptive analyses summarized temporal trends, and annual diversity patterns were quantified using the Shannon diversity index. A linear mixed-effects model compared import volumes between semen types, with year included as a fixed effect, and a fixed-effects model incorporating sire identity quantified the extent to which individual bulls contributed to variation in import demand. Principal component analysis and clustering were used to identify groups of sires with similar genetic and usage profiles. For the most heavily used sires, age-related usage patterns were evaluated by comparing recently released younger sires with older sires possessing longer semen-production histories. Overall, total semen imports peaked in 2021 before declining in subsequent years, accompanied by a substantial reduction in the proportion of sexed semen. Although more than 150 sires were imported annually, usage concentrated on a subset of bulls whose genetic profiles reflected different breeding priorities, including production-oriented, durability-focused, or intermediate strategies. Cluster patterns further indicated that Taiwan's import decisions are shaped by heterogeneous breeding goals and evolving market conditions. These findings provide the first national-scale assessment of Taiwan's semen importation dynamics and offer evidence-based guidance for refining sire selection, improving cost-effectiveness, and supporting sustainable genetic progress in subtropical dairy production systems.