DEVELOPING AN OXYTOCIN TREATMENT PROTOCOL FOR SUPRESSING ESTRUS IN MARES

• Sponsoring Institution: State Agricultural Experiment Station
• Project Status: COMPLETE
• Funding Source: STATE
• Reporting Frequency: Annual
• Accession No.: 1000653
• Project Start Date: Jul 31, 2013
• Project End Date: Jun 30, 2018
• Program Code: [(N/A)]- (N/A)

Recipient Organization
UTAH STATE UNIVERSITY
(N/A)
LOGAN,UT 84322

Performing Department
Animal Dairy & Veterinary Sciences

Non Technical Summary
There remains a need for a practical method of blocking estrous behavior (i.e., "heat") in mares in order to prevent the behavior from interfering with training and performance activities. The most reliable means of blocking estrus in mares involves oral administration of the synthetic steroid hormone altrenogest (ReguMate), which although effective, is expensive, requires long-term daily administration and poses health risks to personnel (particularly women) during handling and administration. In addition, since the use of exogenous steroid hormones in performance horses is facing increased scrutiny, finding alternative methods of estrus suppression is particularly important now. One alternative to ReguMate (and other steroid hormones) is intrauterine insertion of a glass ball (i.e., marble) to extend function of the corpus luteum (CL), which allows continued secretion of a mare's endogenous progesterone from the CL to keep her out of heat; however, the success rate when using a glass ball is extremely variable. In addition, there can be severe adverse consequences following intrauterine placement of a glass ball; specifically, rupture and fragmentation of the glass ball in the uterine lumen or development of a cervical tear when manually removing a glass ball, both of which will severely impair subsequent fertility after a mare's performance career. In order to avoid problems associated with use of an intrauterine glass ball, we have developed an alternative method of extending CL function that uses intramuscular administration of oxytocin to mares. Oxytocin is a small peptide hormone that provides an alternative method of estrus suppression that does not use exogenous steroid hormones. In an initial "proof of principle" study published in the Journal of the American Veterinary Medical Association (Vanderwall et al., 2007;231:1864-1867), we showed that intramuscular administration of 60 units (3 cc) of oxytocin twice daily on days 7 to 14 after ovulation caused prolonged CL function (i.e., continued progesterone secretion through day 30) in all six treated mares, whereas CL function ceased by day 16 in all six control mares. In a follow-up study published in the Journal of Equine Veterinary Science (Vanderwall et al., 2012;32:536-541), we found that once daily administration was as effective as twice daily administration for extending CL function, which simplifies the treatment protocol. Using the once daily oxytocin treatment protocol, we have found that the average duration of extended CL function in treated mares is approximately 2 months. Although our work has shown that oxytocin treatment effectively prolongs CL function, there are two limitations of the current treatment protocol. First, although the duration of extended CL function is approximately 2 months, a longer period of CL function (i.e., 3 to 4 months) would be more beneficial. Second, the current treatment protocol requires knowing the exact day of ovulation, which necessitates monitoring the ovarian status of each mare with transrectal palpation and ultrasonography. The overall goal/objective of this project is to develop an oxytocin treatment protocol that prolongs CL function beyond 2 months and does not require knowing the exact day of ovulation in order to initiate treatment.

Animal Health Component

60%

Research Effort Categories

Basic

10%

Applied

60%

Developmental

30%

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
301	3810	1020	100%

Knowledge Area
301 - Reproductive Performance of Animals;

Subject Of Investigation
3810 - Horses, ponies, and mules;

Field Of Science
1020 - Physiology;

Keywords

equine

horse

mare

estrus

estrus suppression

corpus luteum

oxytocin treatment

endogenous progesterone

Goals / Objectives
One method of suppressing estrus in mares is to prolong function of the corpus luteum (CL), which is the endogenous source of progesterone that keeps mares out of heat naturally. In non-pregnant mares the CL secretes progesterone for approximately two weeks after ovulation and then it stops functioning when the uterus secretes the hormone prostaglandin F2α. Prostaglandin F2α (PGF2α) causes regression of the CL (i.e., luteolysis) by destroying the cells of the CL that produce progesterone. Because of luteolysis, progesterone levels fall and the mare comes back in heat. Lutolysis does not occur in pregnant mares because the embryo in the uterus blocks secretion of PGF2α, so progesterone secretion continues and the mare does not come back into heat. Therapeutically preventing luteolysis to prolong function of the CL (i.e., mimicking an embryo) is one way of suppressing estrus in non-pregnant mares. We have developed a method of using oxytocin treatment to prolong function of the CL in mares. The overall objective of this project is to develop a more practical and effective oxytocin treatment protocol for estrus suppression in mares.

Project Methods
Specific Aim #1: Twenty mares will be used for this study. The reproductive tract of each mare will be examined with transrectal palpation and ultrasonography. Beginning on the day of ovulation (day 0), jugular blood samples will be collected every other day until day 120 for determination of progesterone concentration. On day 7, mares will be randomly assigned to one of two groups (n = 10/group): 1) oxytocin-treated (control) and 2) oxytocin and hCG-treated (experimental group). Beginning on day 7, mares in both groups will be treated with 60 units (3 cc) oxytocin IM once daily through day 14 to induce prolonged CL function. Beginning on day 18, and continuing through day 24, the reproductive tract of mares in both treatment groups will be examined with transrectal palpation and ultrasonography to determine if there was physical evidence they have undergone luteolysis and returned to estrus (i.e., flaccid uterine tone and/or prominent endometrial edema). Mares with evidence of prolonged CL function in the combined oxytocin and hCG-treated group will be monitored until they develop a dominant ("diestrus") follicle >35 mm at which time 2,500 units of hCG will be administered IV to induce ovulation. Specific Aim #2: Study #1:Twenty mares will be used for this study and they will be randomly assigned to two groups (n = 10/group): 1) standard oxytocin treatment (control) and 2) synchronized oxytocin treatment (experimental group). The reproductive tract of each mare in the standard oxytocin treatment group will be examined three times weekly with transrectal palpation and ultrasonography to detect ovulation (day 0), and then beginning on day 7 they will receive 60 units (3 cc) oxytocin IM once daily through day 14. In contrast, the synchronized oxytocin treatment group will not be monitored with transrectal palpation and ultrasonography. Instead, they will receive two treatments with a luteolytic dose of PGF2α IM 14 days apart to synchronize estrus/ovulation. Beginning 14 days after the second PGF2α treatment, each mare will receive 60 units (3 cc) oxytocin IM once daily for 10 days. Jugular blood samples will be collected from the standard oxytocin treatment group every other day beginning on the day of ovulation through day 50 (post-ovulation). Blood samples will be collected from the synchronized oxytocin treatment group every other day beginning 7 days after the second PGF2α treatment through day 50 (after second prostaglandin treatment). Blood samples will be analyzed for progesterone concentration. Study #2:Twenty mares will be used for this study and they will be randomly assigned to two groups (n = 10/group): 1) standard oxytocin treatment (control) and 2) modified oxytocin treatment (experimental group). The reproductive tract of each mare in the standard oxytocin treatment group will be examined with transrectal palpation and ultrasonography until ovulation (day 0) is detected, and then beginning on day 7 they will receive 60 units (3 cc) oxytocin IM once daily through day 14. In contrast, the modified oxytocin treatment group will not be monitored with transrectal palpation and ultrasonography. Instead, treatment with 60 units (3 cc) oxytocin will commence regardless of the exact stage of the estrous cycle (i.e., day post-ovulation) and continue daily for 21 days. Jugular blood samples will be collected from the standard oxytocin treatment group every other day beginning on the day of ovulation through day 50 (post-ovulation). Blood samples will be collected from the modified oxytocin treatment group every other day beginning on the first day of oxytocin treatment and continuing for 50 days. Blood samples will be analyzed for progesterone concentration.

Progress 07/31/13 to 06/30/18

Outputs
Target Audience:Veterinarians Changes/Problems:In 2015, the results of the study involving administration of oxytocin for 29 consecutive days made completion of one of our originally proposed experiments (Study #1 for Specific Aim #2) moot, as they both had the same general goal of developing an oxytocin treatment protocol that does not require determining the day of ovulation in mares. What opportunities for training and professional development has the project provided?On September 28, 2013, a one-hour continuing education seminar for veterinarians entitled "Estrus Suppression" was presented at the Annual Meeting of the Northeast Association of Equine Practitioners in Stamford, CT. How have the results been disseminated to communities of interest?In 2013, proceedings articles accompanying the two continuing education seminars noted above (Annual Meeting of the Northeast Association of Equine Practitioners in Stamford, CT and Annual Meeting of the American Association of Equine Practitioners in Nashville, TN) were published by the respective organizations allowing dissemination of the information to veterinarians who did not attend these seminars. The results of the project involving administration of oxytocin for 29 consecutive days were presented by Kate Parkinson at the 2015 Annual Meeting of the Western Section of the American Society for Animal Science in Ruidoso, NM in June, 2015. An accompanying manuscript was published in the meeting proceedings (vol. 66:48-51). Kate successfully defended her thesis on Oct. 30, 2015, and her MS thesis has been published. Disseminating our research results via these venues/publications has informed scientists and veterinarians of a new protocol for using oxytocin treatment to suppress estrus in mares that does not require detection of ovulation. This will allow the new protocol to be incorporated into clinical treatment protocols for estrus suppression in mares. In 2016, a review article summarizing our work to-date on the use of oxytocin treatment to prolong corpus luteum function in mares for estrus suppression was published in the Journal of Equine Veterinary Science (2016;36:1-4). Disseminating the results of our research has informed veterinarians on the two protocols we have developed for using oxytocin treatment to suppress estrus in mares, allowing them to choose the most appropriate protocol for each clinical situation. In 2017, the written abstract "Effect of human chorionic gonadotropin (hCG) treatment on the duration of oxytocin-induced prolonged corpus luteum (CL) function in mares" that was presented at the Society for Theriogenology meeting was published in Clinical Theriogenology 2017;9(#3):445. In addition, the manuscript that accompanied the presentation "The Hormonal Basis for Reproductive Behavior in Nonpregnant Mares" at the American Association of Equine Practitioners (AAEP) was published in the AAEP Proceedings 2017;63:117-123. Collectively, this resulted in the dissemination of the information to veterinarians who did not attend those meetings. What do you plan to do during the next reporting period to accomplish the goals?The plan of work has been fully summarized in the "Accomplishments" section above.

Impacts
What was accomplished under these goals? The overall objective of this project was to develop a more practical and effective oxytocin treatment protocol for estrus suppression in performance mares. Towards that end, two major studies were completed over the course of this project. The objective of the first study was to determine if administration of 60 units of oxytocin once daily for 29 days, regardless of when treatment was initiated during the estrous cycle, would induce prolonged corpus luteum (CL) function in cycling mares. Mares were randomly assigned to two groups: 1) saline-treated control (n=7) and 2) oxytocin-treated (n=9). Control mares received 3 cc saline and oxytocin-treated mares received 60 units (3 cc) of oxytocin intramuscularly for 29 consecutive days. Treatment was initiated in all mares on the same day (d 1), independent of the day of the cycle. Jugular blood samples for determination of progesterone concentration were collected three times weekly (M, W, F) for 21 days before treatment was initiated. Beginning on the first day of treatment, blood samples were collected daily for seven days, three times weekly for the remainder of the treatment period, and then three times weekly for 45 days after the last treatment. Mares were considered to have prolonged CL function if serum progesterone remained >1.0 ng/mL for at least 30 days during/after the treatment period. The proportion of mares with prolonged CL function was higher in the oxytocin-treated group compared to the saline-treated group (7/9 vs. 1/7, respectively; P<0.05). Three of the seven oxytocin-treated mares that developed prolonged CL function initially underwent luteolysis within 3 to 7 days of the start of oxytocin treatment, and then developed prolonged CL function following the subsequent ovulation during the treatment period. In the other four oxytocin-treated mares that developed prolonged CL function, progesterone remained >1.0 ng/mL throughout the treatment period and into the post-treatment period. All mares with prolonged CL function maintained elevated progesterone concentrations through at least day 56 of the study. In conclusion, the results of this study demonstrated the effectiveness of chronic oxytocin treatment, initiated randomly during the estrous cycle, for prolonging CL function in mares. When mares develop prolonged CL function in response to oxytocin treatment, the CL generally remains functional for 60 to 90 days. However, a longer duration of CL function would be beneficial. We hypothesized that administration of human chorionic gonadotropin (hCG) during the period of oxytocin-induced prolonged CL function would extend the duration of CL function through two mechanisms: 1) a direct luteotrophic effect and/or 2) by inducing ovulation of a diestrus follicle(s) resulting in the formation of a new CL(s) that would function for an additional 60 to 90 days. Therefore, the objective of our second study was to determine if administration of hCG during the period of oxytocin-induced prolonged CL function would extend the duration of CL function. Prolonged CL function was induced in 14 mares by administering 60 units of oxytocin IM once daily on days 7 to 14. Mares were randomly assigned equally to a control group that received no additional treatment and an hCG-treated group that received 2,500 units of hCG IM on days 30, 45, 60, 75 and 90 after ovulation. Jugular blood samples were collected on the day of ovulation and then three times weekly (M, W, F) for 120 days for determination of blood progesterone concentration. The duration of CL function (progesterone >1.0 ng/mL) was compared between control and hCG-treated mares using the Wilcoxon Rank Sum test. The duration of CL function was 78.0 ± 2.8 and 91.4 ± 20.4 days (mean ± SD) in control and hCG-treated mares, respectively, which was not significantly different (P>0.05). Therefore, this study found no benefit of administering hCG during the period of oxytocin-induced prolonged CL function, so alternative methods of extending the duration of CL function should be explored.

Publications

• Type: Journal Articles Status: Published Year Published: 2018 Citation: Vanderwall, D. K., Kinney, D. L., Mason, H., Ambrose, B., & Rigas, J. (2018, July). Evaluation of Three Proprietary Slow-Release Oxytocin Formulations on Corpus Luteum (CL) Function in Mares. Journal of Equine Veterinary Science, 66, 159-160
• Type: Conference Papers and Presentations Status: Other Year Published: 2018 Citation: Vanderwall, D. K. (Presenter & Author), Kinney, D. L. (Author Only), Mason, H. (Author Only), Ambrose, B. (Author Only), Rigas, J. (Author Only), 12th International Symposium on Equine Reproduction, "Evaluation of Three Proprietary Slow-Release Oxytocin Formulations on Corpus Luteum (CL) Function in Mares," Cambridge, England. (July 2018)

Progress 10/01/16 to 09/30/17

Outputs
Target Audience:Veterinarians Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?On March 23, 2017, a 30-minute continuing education seminar for veterinarians entitled "How to Use Oxytocin Treatment to Suppress Estrus in Mares" was presented in Provo, UT. On August 4, 2017, a 15-minute presentation of an abstract entitled "Effect of human chorionic gonadotropin (hCG) treatment on the duration of oxytocin-induced prolonged corpus luteum (CL) function in mares" was given at the Annual Meeting of the Society for Theriogenology in Ft. Collins, CO. On November 17, 2017, a 50-minute continuing education seminar for veterinarians entitled "The Hormonal Basis for Reproductive Behavior in Nonpregnant Mares" was presented at the Annual Meeting of the American Association of Equine Practitioners in San Antonio, TX. How have the results been disseminated to communities of interest?The written abstract presented at the Society for Theriogenology meeting was published in Clinical Theriogenology 2017;9(#3):445 and the manuscript that accompanied the presentation at the American Association of Equine Practitioners (AAEP) was published in the AAEP Proceedings 2017;63:117-123, which collectively will allow dissemination of the information to veterinarians who did not attend those meetings. What do you plan to do during the next reporting period to accomplish the goals?A full-length manuscript describing the results of the hCG-treatment study described above will be prepared and submitted to a research journal for publication.

Impacts
What was accomplished under these goals? The results of the project that were pending last year (for Specific Aim #1) have now been analyzed and were presented at the 2017 Annual Meeting of the Society for Theriogenology in Ft. Collins, CO in August, 2017. The objective of that study was to determine if administration of human chorionic gonadotropin (hCG) during the period of oxytocin-induced prolonged CL function would extend the duration of CL function. Prolonged CL function was induced in 14 mares by administering 60 units of oxytocin IM once daily on days 7 to 14. Mares were randomly assigned equally to a control group that received no additional treatment and an hCG-treated group that received 2,500 units of hCG IM on days 30, 45, 60, 75 and 90 after ovulation. Jugular blood samples were collected on the day of ovulation and then three times weekly (M, W, F) for 120 days for determination of blood progesterone concentration. The duration of CL function (progesterone >1.0 ng/mL) was compared between control and hCG-treated mares using the Wilcoxon Rank Sum test. The duration of CL function was 78.0 ± 2.8 and 91.4 ± 20.4 days (mean ± SD) in control and hCG-treated mares, respectively, which was not significantly different (P>0.05). Therefore, this study found no benefit of administering hCG during the period of oxytocin-induced prolonged CL function, so alternative methods of extending the duration of CL function should be explored.

Publications

• Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Vanderwall, D. K. (2017). The hormonal basis for reproductive behavior in nonpregnant mares (vol. 63, pp. 117-123). Lexington, KY: American Association of Equine Practitioners.
• Type: Other Status: Published Year Published: 2017 Citation: Vanderwall, D. K., Kinney, D. L., Mason, H., Rigas, J. (2017). Effect of human chorionic gonadotropin (hCG) treatment on the duration of oxytocin-induced prolonged corpus luteum (CL) function in mares (3rd ed., vol. 9, pp. 445). Clinical Theriogenology.
• Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Presentations Vanderwall, D. K., American Association of Equine Practitioners, "The hormonal basis for reproductive behavior in nonpregnant mares," San Antonio, TX. (November 19, 2017)
• Type: Conference Papers and Presentations Status: Other Year Published: 2017 Citation: Presentations Vanderwall, D. K. (Presenter & Author), Kinney, D. L. (Author Only), Mason, H. (Author Only), Rigas, J. (Author Only), Annual Meeting of the Society for Theriogenology, "Effect of human chorionic gonadotropin (hCG) treatment on the duration of oxytocin-induced prolonged corpus luteum (CL) function in mares." (August 4, 2017)

Progress 10/01/15 to 09/30/16

Outputs
Target Audience:Target Audience Veterinarians. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided?Opportunities The day-to-day oversight and completion of the project described above was performed by first-year veterinary student, Dustin Kinney, which gave him invaluable research experience. How have the results been disseminated to communities of interest?Dissemination A review article summarizing our work to-date on the use of oxytocin treatment to prolong corpus luteum function in mares for estrus suppression was published in the Journal of Equine Veterinary Science (2016;36:1-4). Disseminating the results of our research has informed veterinarians on the two protocols we have developed for using oxytocin treatment to suppress estrus in mares, allowing them to choose the most appropriate protocol for each clinical situation. In the coming year, results of this project will be presented at scientific meetings and veterinary continuing education meetings; and published in the corresponding proceedings and other professional journals. What do you plan to do during the next reporting period to accomplish the goals?Plan of Work Once the blood progesterone testing is finished, the duration of prolonged CL function will be compared between Control and hCG-treated mares using Wilcoxon's Rank Sum test. If hCG treatment significantly increased the duration of prolonged CL function (induced by oxytocin treatment), it will provide veterinarians with a means of clinically enhancing the efficacy of the oxytocin treatment protocol for estrus suppression in mares (i.e., hCG treatment will cause mares to stay out of heat for a longer period of time).

Impacts
What was accomplished under these goals? Accomplishments The overall objective of this project is to develop a more practical and effective oxytocin treatment protocol for estrus suppression in mares. This year an experiment was conducted to test the hypothesis that administration of human chorionic gonadotropin (hCG) during the period of prolonged function of the corpus luteum (CL) induced by oxytocin treatment would significantly extend the duration of CL function. Fourteen mares were treated with 60 units (3 cc) of oxytocin intramuscularly (IM) once daily on days 7 to 14 after ovulation to induce prolonged CL function, and they were randomly assigned to Control and hCG-treated groups (n=7/group). Control mares did not receive any additional treatment (other than oxytocin), while hCG-treated mares received 2,500 units of hCG IM on days 30, 45, 60, 75 and 90 after ovulation. Jugular blood samples for determination of progesterone concentration were collected on the day of ovulation and then three times weekly (M, W, F) for 120 days. Results are currently pending, while the blood progesterone testing and subsequent statistical analyses are completed.

Publications

• Type: Journal Articles Status: Published Year Published: 2016 Citation: Vanderwall, D. K., Parkinson, K. C., Rigas, J. (2016). How to Use Oxytocin Treatment to Prolong Corpus Luteum Function for Suppressing Estrus in Mares. Journal of Equine Veterinary Science, 36, 1-4.

Progress 10/01/14 to 09/30/15

Outputs
Target Audience:Target Audience Veterinarians. Changes/Problems:Changes/Problems The results of this experiment (Specific Aim #2, Study #2) have made completion of Study #1 (for Specific Aim #2) moot, as they both had the same general goal of developing an oxytocin treatment protocol that does not require determining the day of ovulation in mares. Therefore, we will not pursue completion of Specific Aim #2, Study #1, and instead focus on studying the implementation of the new oxytocin treatment protocol under field conditions. What opportunities for training and professional development has the project provided?Opportunities In addition to the professional development of my MS student, Kate Parkinson, the project provided an opportunity for one veterinary student, Emily Hampden-Smith, to be directly involved in clinical research. How have the results been disseminated to communities of interest?Dissemination The results of this project will be presented at scientific meetings and veterinary continuing education meetings; and published in the corresponding proceedings and other professional journals. What do you plan to do during the next reporting period to accomplish the goals?Plan of Work In the near term, we plan to continue evaluating the efficacy of the new 28-day oxytocin treatment protocol under field conditions. In addition, we plan to evaluate a modification of this oxytocin treatment protocol that would incorporate testing the mare's blood progesterone level on day 10 of oxytocin treatment, because based on our results, oxytocin treatment could be stopped in mares with elevated progesterone, while those with a low progesterone level need to continue receiving oxytocin treatment for the full 28-day period.

Impacts
What was accomplished under these goals? Accomplishments The results of the project that were pending last year (for Specific Aim #2, Study #2) have now been analyzed and presented at the 2015 Annual Meeting of the Western Section of the American Society for Animal Science in Ruidoso, NM in June, 2015. An accompanying manuscript was published in the meeting proceedings (vol. 66:48-51). In addition, a full-length manuscript is now being prepared for publication in a refereed journal. This work formed the basis of my graduate student, Kate Parkinson's, MS thesis. Kate successfully defended her thesis on Oct. 30, 2015, and is now finalizing her written thesis. The results of this study were also included in a review article on using oxytocin to prolong corpus luteum function in mares for estrus suppression (J. Equine Vet. Sci., 2016;36:1-4). Disseminating our research results via these venues/publications has informed scientists and veterinarians of a new protocol for using oxytocin treatment to suppress estrus in mares that does not require detection of ovulation. This will allow the new protocol to be incorporated into clinical treatment protocols for estrus suppression in mares.

Publications

• Type: Other Status: Published Year Published: 2015 Citation: Refereed Journal Articles Turner, R. M., Vanderwall, D. K., Stawicki, R. (2015). Complications Associated with the Presence of Two Intrauterine Glass Balls Used for Estrus Suppression in a Mare. Equine Veterinary Education, 27, 340-343
• Type: Other Status: Published Year Published: 2015 Citation: Refereed Journal Articles Vanderwall, D. K. (2015). Is it Time to Retire the Use of Intrauterine Glass Balls for Estrus Suppression in Mares? Journal of the American Veterinary Medical Association, 247, 346-347.

Progress 10/01/13 to 09/30/14

Outputs
Target Audience: Target Audience Veterinarians. Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? Opportunities The day-to-day oversight and completion of the project described above was performed by my Master's student, Kate Parkinson. This provided Kate with an opportunity to design and conduct the experiment, and she is now performing the progesterone assay, after which she will analyze the data to determine the outcome of the experiment. This project will be the basis for her MS thesis that she will defend and publish. How have the results been disseminated to communities of interest? Dissemination The results of the experiment conducted this year will be published in Kate Parkinson's MS thesis and in a manuscript in an appropriate scientific journal. What do you plan to do during the next reporting period to accomplish the goals? Plan of Work The overall plan of work as originally described, to develop a more practical method of using oxytocin treatment to prolong CL function (as a means of estrus suppression in mares), remains the ultimate goal. Once we have the final results from the 2014 project, we will know whether long-term, daily administration of oxytocin is efficacious. If it is, we can then test that protocol under field conditions.

Impacts
What was accomplished under these goals? Accomplishments To fulfill specific aim #2 (study #2), we completed a research project that tested the hypothesis that administering oxytocin daily for 28 days, regardless of when treatment is initiated during the estrous cycle, would induce prolonged CL function without the need to detect ovulation. Control (n=8) and treated mares (n=9) were randomly assigned to receive daily IM treatments of 3cc saline and 60 units (3cc) oxytocin respectively. Treatment was initiated in all mares on the same day, independent of the day of cycle and continued for 28 days. Blood samples for determination of progesterone concentration were collected three times weekly (M, W, F) for 21 days before treatment was initiated. Beginning on the first day of treatment, blood samples were collected daily for seven days, three times weekly for the remainder of the treatment period and then three times weekly for 45 days after the last treatment. Results are currently pending, waiting for completion of the blood progesterone analysis.

Publications

• Type: Conference Papers and Presentations Status: Other Year Published: 2014 Citation: Conference Proceedings Vanderwall, D. K. (2014). Estrus Suppression (pp. E22-31). Moab, UT: CanyonLands Veterinary Conference.

Progress 07/31/13 to 09/30/13

Outputs
Target Audience: Veterinarians Changes/Problems: Nothing Reported What opportunities for training and professional development has the project provided? On September 28, 2013, a one-hour continuing education seminar for veterinarians entitled “Estrus Suppression” was presented at the Annual Meeting of the Northeast Association of Equine Practitioners in Stamford, CT. On December 10, 2013, a 30-minute continuing education seminar for veterinarians entitled “Prolonging Function of the Corpus Luteum to Suppress Estrus in Mares” was presented at the Annual Meeting of the American Association of Equine Practitioners in Nashville, TN. On December 11, 2013, a 90-minute “Table Topic” discussion session for veterinarians on estrus suppression was co-moderated at the Annual Meeting of the American Association of Equine Practitioners in Nashville, TN. How have the results been disseminated to communities of interest? Proceedings articles accompanying the two continuing education seminars noted above were published by the respective organizations allowing dissemination of the information to veterinarians who did not attend these seminars. What do you plan to do during the next reporting period to accomplish the goals? The overall objective of this project is to develop a more practical and effective oxytocin treatment protocol for estrus suppression in mares. As noted above, an MS graduate student has been recruited to complete experiments that will meet the objectives of this UAES project. The first project that will be completed in 2014 is designed to meet the specific aim of developing an oxytocin treatment protocol that does not require knowing of the exact day of ovulation. For this project, twenty Quarter Horse-type mares will be used and they will be randomly assigned to two groups (N = 10/group): 1) standard oxytocin treatment (control) and 2) synchronized oxytocin treatment (experimental group). The reproductive tract of each mare in the standard oxytocin treatment group will be examined three times weekly with transrectal palpation and ultrasonography. Mares with an ovarian follicle ≥30 mm in diameter and prominent endometrial edema will be examined daily until ovulation (day 0) is detected, and beginning on day 7 they will receive 60 units (3 cc) oxytocin IM once daily through day 14. In contrast, the synchronized oxytocin treatment group will not be monitored with transrectal palpation and ultrasonography. Instead, they will receive two treatments with a luteolytic dose of PGF2α IM 14 days apart to synchronize estrus/ovulation. Beginning 14 days after the second PGF2α treatment, each mare will receive 60 units (3 cc) oxytocin IM once daily for 10 days. Jugular blood samples will be collected from the standard oxytocin treatment group every other day beginning on the day of ovulation through day 50 (post-ovulation). Blood samples will be collected from the synchronized oxytocin treatment group every other day beginning 7 days after the second PGF2α treatment through day 50 (after second prostaglandin treatment). Blood samples will be allowed to clot at room temperature, after which the serum will be recovered and kept frozen at -20 C until progesterone is measured by radioimmunoassay. The proportion of mares in each group with prolonged CL function (i.e., progesterone continuously >1.0 ng/mL through day 50) will be compared between groups using Fisher’s Exact Test with SAS.

Impacts
What was accomplished under these goals? The overall objective of this project is to develop a more practical and effective oxytocin treatment protocol for estrus suppression in mares. Because of the seasonal pattern of reproduction in mares, the first research project for this study will be conducted in the Spring of 2014. In preparation for that, a new graduate student, Kate Parkinson, has been recruited to begin her MS program in January, 2014. For her thesis research, Ms. Parkinson will complete experiments that will meet the objectives of this UAES project.

Publications

• Type: Conference Papers and Presentations Status: Other Year Published: 2013 Citation: Conference Proceedings Vanderwall, D. K. (2013). Prolonging Function of the Corpus Luteum to Suppress Estrus in Mares (vol. 59, pp. 342-349). Lexington, KY: American Association of Equine Practitioners.
• Type: Conference Papers and Presentations Status: Other Year Published: 2013 Citation: Conference Proceedings Vanderwall, D. K. (2013). Estrus Suppression (pp. 34-41). Lockport, NY: Northeast Association of Equine Practitioners.
• Type: Conference Papers and Presentations Status: Other Year Published: 2013 Citation: Presentations Vanderwall, D. K., American Association of Equine Practitioners, "Prolonging Function of the Corpus Luteum to Suppress Estrus in Mares," Nashville, TN. (December 10, 2013)
• Type: Conference Papers and Presentations Status: Other Year Published: 2013 Citation: Presentations Vanderwall, D. K., Northeast Association of Equine Practitioners, "Estrus Suppression," Stamford, CT. (September 28, 2013)