Administration of oxytocin immediately after insemination does not improve pregnancy rates in mares bred by fertile or subfertile stallions.
Abstract: It is probable that reduced pregnancy rates in mares bred to subfertile stallions is attributable, in part, to the reduced number of normal spermatozoa that colonize the oviduct. Administration of oxytocin stimulates both uterine and oviductal contractility. The hypothesis that oxytocin may enhance sperm transport to/into the oviducts, and thereby increase pregnancy rates, was tested in 2 trials. For both trials, fertile estrous mares with follicles > or = 35 mm in diameter were inseminated once at 24 h after administration of 1500 to 2000 U hCG. The inseminate dose was limited to 100 million spermatozoa in order to lower pregnancy rates and thus increase the chance of detecting a treatment effect. Pregnancy status was determined by transrectal ultrasound examination 14 to 16 d after insemination. In Trial 1, 49 mares were inseminated with 4 mL extended semen from 1 of 3 stallions (1 fertile and 2 subfertile males). Immediately after insemination, the mares were administered either 20 U oxytocin or 1 mL saline intravenously. In Trial 2, 51 mares were inseminated with 4 mL extended semen from 1 of 4 stallions (1 fertile and 1 subfertile male used in Trial 1, and 2 additional fertile males). Immediately after insemination, and again 30 min later, mares were administered either 5 U oxytocin or 0.25 mL saline intramuscularly. To test for effects of treatment with oxytocin and for the interaction between semen quality and treatment, a generalized linear mixed regression model was used that accounted for the split-plot design (treatment within stallions), the random effect of stallion, the fixed effect of semen quality, the binary outcome of a single breeding trial, and the varying number of trials per stallion/treatment groups. Three treatment protocols or regimens were used: placebo, 5 U oxytocin injected twice intramuscularly, and 20 units oxytocin injected twice intravenously. Semen was classified as high (fertile stallions) or low (subfertile stallions) quality. No interaction between semen quality and treatment was detected (P > 0.10). The pregnancy rate of mares treated with oxytocin immediately after insemination was 30% (15/50) compared with 50% (25/50) for mares treated with saline immediately after breeding. Administration of oxytocin did not affect pregnancy rates (P > 0.10).
Publication Date: 2000-03-23 PubMed ID: 10729032DOI: 10.1016/s0093-691x(99)80017-xGoogle Scholar: Lookup
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- Clinical Trial
- Journal Article
- Randomized Controlled Trial
Summary
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The essence of this research article is investigating the efficacy of oxytocin in improving pregnancy rates in mares, especially when they have been bred by subfertile stallions. The study concludes that administering oxytocin did not significantly enhance pregnancy outcomes in these scenarios.
Research Context
- The study begins by acknowledging the possibility that low pregnancy rates in mares bred to subfertile stallions could be due to reduced numbers of normal spermatozoa that colonize the oviduct.
- The hormone oxytocin, which stimulates uterine and oviductal contractions, is thought to have the potential to improve sperm transport into the oviducts, and thus boost pregnancy rates.
- This hypothesis was tested in two different trials. The participating mares were all in their fertile period and were inseminated once, 24 hours after the administration of a hCG hormone dose.
- The hCG hormone was administered with the intent to lower pregnancy rates, thus increasing the possibility of discerning a treatment effect.
- The status of the pregnancy was determined 14-16 days after insemination with the help of transrectal ultrasound examinations.
Research Methodology
- In both the trials, the mares were inseminated with 4 mL extended semen from a mix of fertile and subfertile males.
- Immediately after insemination, the mares were given either oxytocin or a saline solution in varying quantities and frequencies, depending on the trial.
- A generalized linear mixed regression model was used to account for the multiple variables in the study such as treatment, semen quality, the random factor of the stallion, and the binary outcome of a single breeding trial.
Research Findings
- Three different treatment protocols were used in this study: Placebo, 5 U oxytocin given intramuscularly twice, and 20 units oxytocin injected twice intravenously.
- Semen was classified into two categories: ‘high’ (from fertile stallions) or ‘low’ (from subfertile stallions).
- No significant interaction was found between semen quality and treatment (P > 0.10).
- When comparing pregnancy rates, 30% (15/50) of mares treated with oxytocin became pregnant, versus 50% (25/50) of mares that received a saline treatment.
- Based on these findings, the researchers concluded that oxytocin administration did not significantly affect pregnancy rates (P > 0.10).
Article Conclusion
- The study indicates that the administration of oxytocin immediately after insemination does not bolster pregnancy rates in mares, regardless of whether they were bred by fertile or subfertile stallions.
- This research thus debunks the hypothesis that oxytocin might improve sperm transport and thereby increase pregnancy rates.
Cite This Article
APA
Rigby S, Hill J, Miller C, Thompson J, Varner D, Blanchard T.
(2000).
Administration of oxytocin immediately after insemination does not improve pregnancy rates in mares bred by fertile or subfertile stallions.
Theriogenology, 51(6), 1143-1150.
https://doi.org/10.1016/s0093-691x(99)80017-x Publication
Researcher Affiliations
- Department of Large Animal Medicine and Surgery, College of Veterinary Medicine, Texas A&M University, College Station 77843-4475, USA.
MeSH Terms
- Animals
- Female
- Fertility
- Horses / physiology
- Insemination, Artificial / veterinary
- Male
- Oxytocin / administration & dosage
- Pregnancy
- Semen / physiology
- Treatment Outcome
Citations
This article has been cited 2 times.- Maischberger E, Irwin J, Carrington S, Duggan V. Equine post-breeding endometritis: A review. Ir Vet J 2008 Mar 1;61(3):163-8.
- Brooks J, Maeda T, Ringhofer M, Yamamoto S. Oxytocin homogenizes horse group organization. iScience 2024 Jul 19;27(7):110356.
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