Semen Assessment as a Fertility Predictor in Stallions

Semen assessment as a fertility predictor - view of morphological defects projected in an enlargement from a microscope sitting on a lab benchAccurate stallion semen assessment as a fertility predictor need not rely on expensive equipment. This study investigated whether basic light microscopy assessments of sperm motility, membrane integrity, and morphology could reliably distinguish fertile from sub-fertile stallions under field conditions.

Study Design:

  • 24 frozen semen batches from 24 Arabian and Straight Egyptian Arabian stallions
  • Semen frozen across Europe and the Middle East; used for artificial insemination in Doha, Qatar
  • All straws standardized at 100 million sperm cells; thawed at 37°C for 1 minute
  • Eosin-Nigrosin stain (Botuvital, Botupharma) used to assess membrane integrity and morphology under light microscopy
  • 200 cells evaluated per sample; categorized as major, minor, total, and non-compensatory defects
  • Mares inseminated once at ovulation; pregnancy confirmed by ultrasound at 14 days

Key Results:

  • Major sperm pathologies, total pathologies, and non-compensatory defects were all significantly associated with pregnancy outcome (p<0.05)
  • Total motility, progressive motility, and membrane integrity showed no significant difference between pregnant and non-pregnant groups
  • Non-compensatory defects — those not offset by increasing sperm concentration — were the strongest differentiator (p=0.0099)

Conclusions:

  • Sperm morphology, not motility or membrane integrity, is the critical predictor of fertility in frozen stallion semen
  • Simple, low-cost light microscopy morphology assessment is an effective and field-applicable fertility screening tool
  • Routine evaluation of non-compensatory morphological defects should be prioritized in semen assessment as a fertility predictor

(Amorim GBAG, Oliveira OM, Papa FO, Dell’Aqua Jr JA, Alvarenga MA, Freitas-Dell’Aqua CP. 2025. Can a simple and cheap semen assessment help with fertility? JEVS 145:105262 – Presented in Association with and by Permission of the International Society for Equine Reproduction)