PSI-2 Analysis of Boar Semen Microbiome and Sperm Quality Parameters

Abstract Bacterial contamination of non-frozen extended boar semen has been associated with a decrease in sperm viability and longevity. The objective of this study was to analyze the microbiome of extended boar semen and sperm quality parameters 1) between studs 2) over time and 3) between pooled and single-sire doses. Sixteen pooled (n=4 per stud) and single-sire (n=4 per stud) boar semen doses (80mL) were obtained from two studs (A vs. B). Pooled doses were the composite of boars in single-sire doses. Doses were stored at 16°C and subsampled 16mL daily for five days post-collection. Each day, 5mL were flash frozen and stored at -80°C for bacterial analysis targeting the V4 hypervariable region of the 16S rRNA gene. The remaining 11mL were used to assess sperm progressive motility and agglutination (0: no adhesion to 3: >50% adhesion) by two evaluators with 10 visual estimates per sample. Negative controls of each pooled (n=2 per stud) and single-sire (n=4 per stud) dose remained unopened until day 5. Statistical analyses were conducted using GLM procedure in SAS. Sperm agglutination was greater in stud A than B (1.6 vs. 1.0 ± 0.1, respectively; P< 0.01). Sperm motility tended (P=0.09) to be greater in stud B than A doses (67.4% vs. 61.5% ± 0.02%, respectively), and decreased over time (P< 0.01). Stud B had a greater relative abundance of Proteobacteria (60.0% vs. 47.2% ± 1.5%, respectively; P< 0.01) and lower abundance of Firmicutes (22.5% vs. 31.9% ± 1.4%, respectively; P< 0.01) compared to stud A. Bacterial load did not differ by stud or dose type but increased from day 1 to 3 (P< 0.01). Bacterial load between days 3, 4, and 5 post-collection was not different from the negative control. Results indicate differences in the microbiome between boar studs and its influence on semen over time.