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Scientific reports2017; 7; 44339; doi: 10.1038/srep44339

Quality of seminal fluids varies with type of stimulus at ejaculation.

Abstract: The theory of ejaculate economics was mainly built around different sperm competition scenarios but also predicts that investments into ejaculates depend on female fecundity. Previous tests of this prediction focused on invertebrates and lower vertebrate, and on species with high female reproductive potential. It remains unclear whether the prediction also holds for polygynous mammals with low female reproductive potential (due to low litter size and long inter-birth intervals). We used horses (Equus caballus) to experimentally test whether semen characteristics are adjusted to the oestrous cycle of the mare a stallion is exposed to during few moments before ejaculation. We analysed 122 weekly semen samples collected from 16 stallions during exposure to either an oestrous or a dioestrous mare. Semen volume and the rate of motile sperm were higher when stallions were exposed to an oestrous than to a diestrous mare, while total sperm counts and sperm velocity remained unchanged. Sperm collected after exposure to an oestrous mare also showed reduced oxidative degeneration of cell membranes over a period of 48 hours. We conclude that stallions invest more into their seminal fluids when the chance of fertilization is elevated, and that this adjustment of ejaculate quality can happen very quickly.
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Publication Date: 2017-03-13 PubMed ID: 28287188PubMed Central: PMC5347088DOI: 10.1038/srep44339Google Scholar: Lookup
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Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

This research article investigates whether the type of stimulus at ejaculation in male horses affects the quality of their seminal fluids, given the female’s reproductive stage. The study found that exposure to an oestrous (reproductively active) mare resulted in higher semen volume and motile sperm rate, suggesting that stallions adjust ejaculate quality to the female’s reproductive stage.

Understanding Ejaculate Economics

  • The research paper is based on a theory of ejaculate economics, which has primarily been focused around various sperm competition scenarios.
  • This theory suggests that the investment that males put into their ejaculates depends on female fecundity, or the female’s ability to produce offspring.
  • Prior tests of this theory mainly focused on invertebrates and lower vertebrates – and particularly on species where the female has a high reproductive potential. This study extends the scope to mammals.

Focus on Polygynous Mammals

  • The research aimed to clarify whether predictions based on ejaculate economics theory hold true for polygynous mammals (those with multiple mates) with low female reproductive potential.
  • This low reproductive potential can be due to factors such as low litter size and long inter-birth intervals, which are characteristic of horses – the focus of this study.

Experimental Methodology

  • The experiment involved collecting weekly semen samples from 16 stallions that were exposed to either an oestrous (reproductively active) or a dioestrous (not reproductively active) mare.
  • In total, 122 semen samples were analysed, measuring semen volume, rate of motile (active) sperm, total sperm counts, and sperm velocity.

Findings and Implications

  • The results showed that stallions produced larger semen volumes and higher rates of motile sperm upon exposure to an oestrous mare as compared to a dioestrous one.
  • However, total sperm counts and sperm velocity remained unaffected by the female’s reproductive state.
  • Interestingly, sperm extracted after exposure to an oestrous mare also revealed reduced oxidative degeneration of cell membranes over a period of 48 hours.
  • This suggests that stallions invest more in their seminal fluids when there is a larger perceived chance of fertilization and this change in ejaculate quality can occur rapidly.
  • Such findings contribute to our understanding of reproductive behavior and strategies in mammals, and point to the potential impact of external factors on semen quality.

Cite This Article

APA
Jeannerat E, Janett F, Sieme H, Wedekind C, Burger D. (2017). Quality of seminal fluids varies with type of stimulus at ejaculation. Sci Rep, 7, 44339. https://doi.org/10.1038/srep44339

Publication

Scientific reports
ISSN: 2045-2322
NlmUniqueID: 101563288
Country: England
Language: English
Volume: 7
Pages: 44339
PII: 44339

Researcher Affiliations

Jeannerat, E
  • Swiss Institute of Equine Medicine ISME, Agroscope and University of Berne, Avenches, Switzerland.
Janett, F
  • Clinic of Reproductive Medicine, University of Zurich, Zurich, Switzerland.
Sieme, H
  • Unit for Reproductive Medicine - Clinic for Horses, University of Veterinary Medicine Hanover, Hanover, Germany.
Wedekind, C
  • Department of Ecology and Evolution, Biophore, University of Lausanne, Lausanne, Switzerland.
Burger, D
  • Swiss Institute of Equine Medicine ISME, Agroscope and University of Berne, Avenches, Switzerland.

MeSH Terms

  • Animals
  • Ejaculation / physiology
  • Estrus / physiology
  • Female
  • Horses
  • Male
  • Semen / cytology
  • Semen / physiology
  • Semen Analysis / methods
  • Semen Analysis / veterinary
  • Sexual Behavior, Animal
  • Sperm Count / veterinary
  • Sperm Motility / physiology

Conflict of Interest Statement

The authors declare no competing financial interests.

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