Standardization of bovine sperm concentration analysis in a multi-laboratory setting

Sperm concentration evaluation is a fundamental component of semen analysis, as results are critical for clinical management and preparation of semen for assisted reproduction. However, significant variations in sperm concentration measurements have been reported within and across laboratories. The objective of this study was to assess the effectiveness of standardization of bull sperm concentration analysis in a multi-laboratory setting. In Experiment I, NucleoCounter calibration (27 units, seven laboratories) was evaluated using frozen reference standards analyzed weekly over 12 weeks by the same technician in each laboratory. NucleoCounter performance was satisfactory and the few data points flagged on Levey-Jennings charts seemed to result from systemic errors introduced by the technician. The intra-technician coefficient of variation (CV) was 2.2 ± 1.8 % (mean ± SD), while the intra-equipment CV was 4.0 ± 1.3 %. In Experiment II, the effect of customized e-learning training was evaluated across six laboratories. When compared to results obtained before training, CV for duplicate results (3.2 ± 3.8 %) and proportion of samples with duplicate results differing by more than 10 % (8.1 %) decreased (P < 0.05) after training (3.0 ± 3.2 % and 6.9 %, respectively). In Experiment III, 10 batches of frozen semen were produced with three replicates of each batch coded differently. Sperm concentration was evaluated by nine technicians across six laboratories during three test periods over one year. Intra-technician and intra-batch CV were 3.4 ± 3.1 % and 4.6 ± 2.2 %, respectively. When Bland-Altman plots showed that the mean difference of individual results and the overall mean was close to zero during all test periods (-0.36 to 0.55 × 10⁶ sperm/mL for the 17 × 10⁶ sperm/mL standard and -2.2 to 3.5 × 10⁶ sperm/mL for the 150 × 10⁶ sperm/mL standard). In conclusion, precise and accurate sperm concentration results were obtained by qualified technicians using standardized procedures and the NucleoCounter.