LAUSR

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+).