Predicting equine fertility using chilled semen

The primary objective of this study was to establish if analysis of a stallion ejaculate may be used to accurately predict if an artificial insemination would result in pregnancy. This study was based on 46 inseminations of 41 mares, by a cohort of 7 standardbred stallions over a 5-week period at an Australian pacing stud. For the analysis, semen quality was assessed immediately after collection, and again after the semen has been chilled at ~5 oC for 24 h. This assessment involved an initial evaluation of the raw or extended ejaculate (for chilled samples), in terms of ejaculate volume, sperm concentration, and motility parameters. These criteria were assessed by use of an iSperm® Equine portable device. Following the preliminary assessment, a sample of the ejaculate were subjected to a migration assay through a 5 µm polycarbonate filter in a Samson™ isolation chamber over a 15 min period. This subpopulation of cells were again assessed for their concentration and motility parameters. Additionally, their ability to reduce the membrane impermeant tetrazolium salt WST-1 was evaluated. This information combined with data that described the stallion and mare’s ages, were used to predict the event of pregnancy, as confirmed by rectal ultrasound performed 14 days post ovulation. The criteria used to predict pregnancy in the subsequent multivariate discriminate analysis was optimized for each individual stallion, resulting in the ability to predict the outcome of an insemination with an overall accuracy of 87.9% if analysed pre-chilling, and 95% if analysed post-chilling.