Frozen Semen Use in Barren Mares

More and more breeders are employing the use of frozen semen and success rates are increasing, reported Sandro Barbacini, DVM, of Select Breeders Services in Italy during his presentation at the 2008 American Association of Equine Practitioners convention, held Dec. 6-10 in San Diego, Calif. Included among the reasons for increased usage, Barbacini said, is that many major registries are now allowing artificial insemination with frozen-thawed semen.

Techniques for freezing and thawing semen have improved, and conception rates using frozen semen have gone up. "It has generally been stated that frozen semen should not be used for insemination of barren mares," Barbacini said. "However, limited data are available on comparison of fertility of barren mares bred with fresh versus frozen-thawed semen. Additionally, factors affecting the fertility of barren mares bred with frozen-thawed semen generally have not been examined."

To rectify the lack of information problem, Barbacini and colleagues launched a study to determine the fertility of barren mares inseminated with either fresh or frozen-thawed semen. Researchers investigated the effects of mare age and uterine fluid, and they worked to determine the number of inseminations with frozen-thawed semen required per pregnancy.

Involved in the study were 285 mares of various breeds that were bred with frozen-thawed semen during breeding seasons from 1998 through 2007. The mares ranged in age from 3 to 21. The frozen-thawed semen came from various laboratories. Forty-six stallions were used. The 285 mares inseminated with frozen-thawed semen were inseminated for a total of 544 cycles.

Following is the scorecard, in part:

  • There were 202 pregnancies.
  • The overall pregnancy rate computed to 71%.
  • The per-cycle pregnancy rate for mares 10-16 years of age was 41% (41% of mares in this age group conceived on the first insemination attempt).
  • The per-cycle pregnancy rate for mares 3-9 years was 38%.
  • The per-cycle pregnancy rate for mares older than 16 was 23%.
  • Overall pregnancy rates were 71% for mares 3-9 years; 76% for mares 10-16 years; and 48% for mares older than 16.

Fluid accumulation in the uterus, when it occurred, was treated with oxytocin (which causes the uterus to contract and clear the fluid) and/or lavage.

Barbacini's take-home message: "Pregnancy rates of barren mares inseminated with frozen semen are reasonable and similar to artificial insemination with fresh semen as long as mares are under 16 years of age. Treatment with oxytocin and/or uterine lavage seemed to improve fertility."

About the Author

Les Sellnow

Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at or by calling 800/582-5604.

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