Association of equine sperm population parameters with outcome of intracytoplasmic sperm injections

Limited clinical information is available regarding sperm population parameters that are important for use with equine intracytoplasmic sperm injection (ICSI). Therefore, the appropriateness of a sample of sperm is typically not known before ICSI. The aim of our study was to determine which sperm population characteristics were predictive of ICSI outcome. Frozen-thawed sperm samples (n = 114) from 37 stallions in a clinical program were analyzed after ICSI for percentages of normal morphology (MORPH+), live as assessed by eosin/nigrosin stain (LIVE+), membrane intact as assessed by hypoosmotic swelling test (HOS+), and DNA fragmentation determined by sperm chromatin dispersion (DNA-). ICSI was performed on 147 oocytes, and cleavage (≥2 cells), embryo development (morula or blastocyst), and pregnancy status after embryo transfer were determined. Among the examined sperm parameters, LIVE + correlated positively with MORPH+ and HOS+, and MORPH + negatively with DNA-; no other significant correlations were observed. When used for ICSI, sperm population percentages for MORPH+ and DNA- were not predictive of ICSI outcome, including cleavage, embryo development, and establishment of a pregnancy. Sperm population percentages significantly affecting ICSI outcomes were LIVE+ and HOS + for oocyte cleavage, LIVE + for embryo development, and HOS + for establishment of a pregnancy. The probability of a pregnancy was significantly higher for sperm populations having HOS+ ≥40% than populations having HOS+ ≤20%. The mean age of the donor mare per sperm-injected oocyte did not differ for oocyte cleavage, embryo production, or establishment of pregnancy. In our study, the probability of sperm-injected oocytes to develop into an embryo (morula or blastocyst) improved when sperm were selected from a population with higher indicators of membrane integrity (LIVE+ and HOS+).