Effect of Osmolarity and Density of Colloid Formulations on the Outcome of SLC-Selection of Stallion Spermatozoa

The osmolarity and density of colloids used to prepare spermatozoa for assisted reproduction may affect sperm quality in the resultant preparation. In this study, two osmolarities of Androcoll-E for single-layer or density gradient centrifugation of stallion spermatozoa were compared: “normal” (320 mOsm) or “high” (345 mOsm). Mean yields for the two centrifugation techniques did not differ between treatments or osmolarities (single layer centrifugation: 30.19 ± 16.9 × 10 6 and 25.8 ± 18.5 × 10 6 spermatozoa; density gradient centrifugation: 31.84 ± 19.7 × 10 6 and 26.46 ± 20.0 × 10 6 spermatozoa respectively for the two osmolarities). However, use of the high osmolarity colloid for single layer centrifugation increased the proportion of morphologically normal spermatozoa ( P < .05). Therefore, increasing the osmolarity of the colloid formulation may be beneficial for processing ejaculates containing a high proportion of abnormal spermatozoa by SLC. Reducing the density of the colloid used for the SLC substantially increased the yield of motile spermatozoa compared to the normal density colloid (mean ± SD: 72.6 ± 28.9 × 10 6 versus 28.9 ± 24.7 × 10 6 ), while also prolonging sperm survival by 24 hours compared to the uncentrifuged ejaculate. This increased yield may render Single Layer Centrifugation practical for use in the field.