Keeping Stallions' Genital Microflora in Check

Keeping Stallions' Genital Microflora in Check

Aurich said the increase in external bacteria—despite the handlers following the hygienic measures put forth in the European guidelines—could be explained by repetitive coverings during the breeding season.

Photo: Anne M. Eberhardt/The Horse

The amount of genital microflora (bacteria) residing on a stallion's penis and surrounding areas can fluctuate during a breeding season. However, using proper and sterile management techniques can help ensure microflora increases do not affect semen quality or put the mare at risk for reduced fertility or disease, European researchers learned.

When owners manage breeding stock used in artificial insemination (AI) programs according to the European guidelines, only harmless bacteria should survive and flourish during the breeding season, said Christine Aurich, DVM, PhD, head of the Graf Lehndorff Institute for Equine Science in Neustadt, Germany.

The European guidelines for a sterile environment in AI breeding programs recommend:

  • Using a sterile artificial vagina for collection;
  • Handlers wash their hands between handling different stallions;
  • Housing stallions away from other horses and isolating them from other horses in collection settings; and
  • Preventing the stallions’ genitalia from coming in contact with a mare’s genitalia.

Furthermore, European guidelines do not call for washing the stallion’s external genitalia, unlike the guidelines many American breeding centers follow, Aurich said.

“Washing is not painful, and many stallions do tolerate this without problems,” she said. “However, washing may severely disturb the physiologic microflora on the external genitalia. Balanced growth of ‘good’ bacteria on the penile surface is important to inhibit the growth of pathogenic bacteria. If this balance gets disturbed, harmful bacteria may overgrow the good bacteria, infect the stallion, or come into the semen during collection. (The bacteria) can impair semen quality during storage or cause endometritis in a mare after AI.”

Aurich and her fellow researchers, including Stephanie Pasing, PhD, also of the Graf Lehndorff Institute, performed a pioneering study on the evolution of stallions’ microflora status during a breeding season. Every four weeks, from February to August, the team evaluated microflora from 16 stallions' urethral openings, urethral fossas, penile sheaths, and semen. All of the stallions were collected at the same stud farm in Neustadt.

The team found that ‘good’ bacterial populations increased over time in the majority of the stallions, and the greatest increases were found on the external genitalia, rather than in the urethral fossa or semen, Aurich said. What’s more, pathogenic (disease-causing) bacteria were rarely seen, and the stallions' semen quality remained consistent from the beginning of the season to the end, she relayed.

Aurich said the increase in external bacteria—despite the handlers following the hygienic measures put forth in the European guidelines—could be explained by repetitive coverings during the breeding season.

“Semen collection (and also natural cover) presents a certain stress to the penile surface,” she explained. “The mechanical stress (contact between surface of the penis and the artificial vagina together with the stallion's vigorous thrusting) causes microlesions of the penile surface. There are tiny injuries all over the surface that can hardly be seen. Combined with the reaction of the organism to heal these lesions, they can disturb the balance of the microflora,” leading to bacterial overgrowth.

The increased workload breeding center personnel experience during peak season could also lead to “less than perfect handling” with less hygienic measures, she added. While not ideal, handlers might go faster than usual and spend less time cleaning up when many stallions must be collected in a single day than they would on days fewer stallions are collected.

The researchers also used this study to test a new analysis technique for examining microflora. Aurich said they found the technique—called MALDI-TOF-MS (matrix assisted laser desorption/ionization time-of-flight mass spectrometry)—to be both low-cost and more efficient than traditional analysis methods.

“It’s a great method,” she said. “Unfortunately, it’s not available in many laboratories yet … but hopefully this will change in due course.”

The study, "Development of the genital microflora in stallions used for artificial insemination throughout the breeding season," was published in Animal Reproduction Science

About the Author

Christa Lesté-Lasserre, MA

Christa Lesté-Lasserre is a freelance writer based in France. A native of Dallas, Texas, Lesté-Lasserre grew up riding Quarter Horses, Appaloosas, and Shetland Ponies. She holds a master’s degree in English, specializing in creative writing, from the University of Mississippi in Oxford and earned a bachelor's in journalism and creative writing with a minor in sciences from Baylor University in Waco, Texas. She currently keeps her two Trakehners at home near Paris. Follow Lesté-Lasserre on Twitter @christalestelas.

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