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Antioxidants and Cooled Stallion Semen QualityBy Kentucky Equine Research Staff · February 14, 2017

Cooling and shipping semen from stallions sometimes results in decreased fertility in artificial insemination programs. Several explanations have been proposed over the years to explain this decreased sperm quality, including:

  • Semen collection technique (e.g., choice of artificial vagina);
  • Chemical composition of the extenders used to dilute and preserve the semen samples;
  • The centrifugation process used during sample processing prior to cooling and shipping; and
  • The cooling technique causing “cold shock” to the spermatozoa that decreases cell viability, motility, and therefore fertilization ability.

Another proposed hypothesis to explain poor spermatozoa performance following cooling involves the production of high levels of free radicals, such as reactive oxygen species, that damage sperm cell membranes.

With this in mind, several research groups attempted to add antioxidants to collected semen samples to protect the spermatozoa from free radical damage. Examples of such antioxidants include resveratrol, pyruvate, melatonin, superoxide dismutase, and quercetin. Results from studies involving those antioxidants were conflicting, but some benefits were noted.

Green tea contains a number of antioxidants, including a group of natural antioxidants called polyphenols, as well as epigallocatechin-3-gallate (EGCG). These two antioxidants were recently added* to stallion semen extender to determine their impact on semen motility, viability, and acrosome and DNA integrity. Unfortunately, no beneficial effect in equine cooled semen was identified after the addition of the either polyphenols or EGCG to the extender.

“Another approach to improving semen quality involves dietary supplementation with antioxidants or with omega-3 fatty acids to maintain or improve the integrity of sperm cell membranes during the cooling or freezing process,” shared Kathleen Crandell, Ph.D., a nutritionist with Kentucky Equine Research (KER).

Some studies support dietary supplementation with omega-3 fatty acid products like EO•3 to improve stallion semen in artificial insemination programs. EO•3 contains marine-derived DHA and EPA, and is available in a palatable top-dress formulation.

*Bucci, D. M. Spinaci, B.Mislei, et al. Epigallocatechin-3-gallate (EGCG) and green tea polyphenols do not improve stallion semen parameters during cooling at 4°C. Reproduction in Domestic Animals. In press.