Breeding horses: how Selsaf® contributes to good fertility

Breeding horses: how Selsaf® contributes to good fertilityThe effect of selenium on reproductive functions has been little studied in both males and females. Nevertheless, selenium is known to be involved in several pregnancy-related complications, such as preeclampsia, autoimmune thyroid disease, miscarriage, and premature birth in humans. Veterinary medicine, meanwhile, associates selenium deficiency with the impairment of fertilisation, mastitis-metritis-agalactica in swine, retained placenta, embryonic mortality, and cystic ovaries. Supplementing a mare’s daily diet with adequate quantities of selenium is usually advised. This result in an increase in fertility which is undoubtedly due to a decrease in embryonic mortalities during the first month of gestation. In addition, recent studies have shown that selenium and selenoproteins may also play a role in oocyte development and ovarian physiology (Qazi & al., 2018).

Selenium and selenoproteins appear to improve oxidative and nitrosative stress in relation to assisted reproductive technologies, such as FIV in humans or embryo transfer in veterinary medicine. However, their role in relation to females remains unclear (Qazi & al., 2018). This is a limiting point, given the importance of assisted techniques in equine reproduction. Fortunately, the effect of selenium on the reproductive function of stallions is better understood.

Breeding practices increase oxidative stress and have a detrimental impact on equine fertility.

In stallions, the main feature of sperm cells is their high level of membrane lipids. Seen as polyunsaturated fatty acids (PUFAs), lipids give the membrane its high level of fluidity and elasticity, factors which are both necessary for sperm motility and fusion with oocytes. However, this characteristic has a downside: it makes them particularly vulnerable to oxidation.

Stallion spermatozoa are “active producers” of reactive oxygen species (ROS) due to their intense mitochondrial activity. Although they are necessary for many essential aspects of spermatozoa functionality, ROS attack cell membranes by causing lipid peroxidation. Excessive release of ROS triggers oxidative stress, leading to a loss of membrane fluidity and integrity. This loss reduces the ability of sperm to accomplish fertilisation (Peña & al., 2019).

In equine reproduction, breeding practices tend to increase the negative effect of oxidative stress on stallion fertility.

With the exception of racing thoroughbreds, whose careers are relatively short, sports horses are used for breeding quite late in life, once they have proved their sporting potential. Unfortunately, the ageing process increases levels of lipid peroxidation. In addition, due to oxidative stress, the quality of the sperm plasma membrane is negatively affected, influencing stallion fertility.


Furthermore, artificial insemination with frozen semen, as is mainly used with sports horses, requires the implementation of cryopreservation methods. This increases the effect of oxidative stress on the sperm. The detrimental effect of cryopreservation, which increases lipid peroxidation after freezing and thawing, is linked to an excessive production of ROS. Subsequent oxidation leads to an overall reduction in sperm quality and fertilisation rates. (Qazi & al., 2019).

In males, increased selenium supply is linked with improved sperm quality and fertility.


Selenium is an essential component of selenoproteins, a large number of which have antioxidant properties. The best known selenoprotein is Glutathione peroxidase (GPx), a potent antioxidant which reduces lipid peroxidation. It may also be viewed as a storage reservoir for Se in cells.

A drop in selenium levels has been observed in tests on mice which were fed a selenium-deficient diet. The recorded decrease in selenium was accompanied by a reduction in GPx activity and an increase in lipid peroxidation. In contrast, an increase in Se in the diet resulted in enhanced antioxidant glutathione peroxidase (GPx) activity, thereby improving male fertility. From these, and other similar studies, it appears obvious that selenium is essential to aid spermatogenesis and male fertility. This is presumably because of the vital role of Se in the modulation of antioxidant defence mechanisms and other essential biological pathways (Qazi & al., 2019).

Horse fertility

In horses more specifically, semen selenium levels have been found to influence fertility markers, such as sperm quality and pregnancy rate per oestrus cycle. Adequate selenium content is thus seen as a necessary condition for good sperm quality and fertility in stallions (Bertelsmann & al., 2010).

Using Selsaf® – a highly bioavailable organic source of selenium – to reduce oxidative damage in stallion semen and to protect embryo and foetus development during pregnancy.


Selsaf® is an approved additive for use with all animal species (FEEDAP, 2020). Produced from the cultivation of a proprietary Saccharomyces cerevisiae (CNCM I-3399) strain, on a medium enriched with Selenium, Selsaf® contains both Selenocysteine and Selenomethionine, two major biologically active seleno-organic compounds. Thanks to a reliable and standardised production process, the concentration in organic Se is high, while the profile of Selsaf®’s active seleno-compounds is stable and consistent.

Once ingested, Selsaf® compounds are actively absorbed into the small intestine by transporter systems. Their absorption is much more efficient than that for sodium selenite, which is transported passively. Due to its composition, Selsaf® can be compared to a twostage rocket:

  • For immediate action, Selenocysteine offers natural protection against oxidative stress via selenoenzymes, such as glutathione peroxidase (GPx).
  • For longer-term action, Seleno-Methionine (63% at least , of organic form present in Selsaf®) is incorporated and stored in the muscles, where it can be mobilised when needs increase; for example, during
    the breeding season for both mares and stallions and during pregnancy.

Studies measuring GPx activity in various animal species indicate that Selsaf® is efficiently used for the construction of functional GPx. Due to Selsaf®’s seleno-organic compounds, GPx activity reaches a higher level than what is obtained from mineral selenium, such as selenite. This better efficiency thus improves cellular protection against oxidation.

Horse fertility

In summary, the dual effect of Selsaf® enhances selenoprotein GPx activity and increases antioxidant defence in breeding horse, reducing oxidative damage. As a result, better reproduction success can be reached.


Bertelsmann, H., & al., a. (2010). Selenium in blood, semen, seminal plasma and spermatozoa of stallions and its relationship to sperm quality. Reproduction Fertility and Development(22(5)), 886-91.

FEEDAP. (2020). Assessment of the application for renewal of authorisation of seleniumenriched yeast produced by Saccharomyces cerevisiae CNCM I-3399 for all animal species. EFSA Journal 2020, 18(5):6144 (

Peña, F., & al., a. (2019). Redox Regulation and Oxidative Stress: The Particular Case of the Stallion Spermatozoa. Antioxidants, 8(11), 567 (

Qazi, I., & al. (2018). Selenium, Selenoproteins, and Female Reproduction: A Review. Molecules (Basel, Switzerland), 23(12), 3053 (

Qazi, I., & al., a. (2019). Role of Selenium and Selenoproteins in Male Reproductive Function: A Review of Past and Present Evidences. Antioxidants(8), 268 (doi:10.3390/antiox8080268).

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