Use of refractometry as a new management tool in AI boar centers for quality assurance of extender preparations

• Boar sperm quality is affected by inexact extender preparation.
• The refractive-index correlates with osmolality in boar semen extenders.
• The sensitivity is sufficient to detect deviations from correct extender preparation before sperm damage occurs.
• Refractometry can be used as quality control tool for boar semen extender preparation.

A study was performed to see if refractometry can be used as a new quality control tool for boar semen extenders. For this the refractive index and osmolality of BTS extender concentrations (EC) were recorded in 10%-steps from 50% to 150% and 200% of the correct amount. Twelve boar ejaculates were evaluated for semen quality. The refractive index for the correctly prepared extender was 4.6 ± 0.0 °Bx, corresponded to 316 ± 16 mOsm kg−1, and correlated highly with osmolality (r = 0.99; P < 0.001). Total sperm motility with 100% EC differed significantly from ≤70% EC (P < 0.001) and 200% EC (P < 0.001) on day 1 (d1) and d4, respectively. The percentage of motile spermatozoa in a thermoresistance test on d2 showed a significant drop using ≤70% EC (P = 0.047) and ≥140% EC (P = 0.004). Secondary apical ridge defects were significantly higher using 50% EC (P < 0.001) and ≥150% EC (P = 0.032) compared to 100% EC, respectively. An increased number of coiled tails were observed using ≤60% EC (P < 0.001). Percentages of spermatozoa with intact membranes on d2 resulted in a significant decrease using 50% EC (P < 0.001) and ≥150% EC (P = 0.005), respectively. The mean percentage of PI negative spermatozoa with active mitochondria on d2 showed a significant difference using ≤60% EC (P = 0.016) and ≥140% EC (P < 0.001) compared to 100% EC, respectively. Boar sperm quality is affected by inexact extender preparation. The refractive-index is an indicator of osmolality and may be used to verify semen extender preparation. The sensitivity is sufficient to detect deviations from correct extender preparation before negative effects on sperm quality occur.