PREGNANCY LOSS IN CATTLE: MAINTENANCE OR REGRESSION OF THE CORPUS LUTEUM BEYOND CLASSICAL MATERNAL RECOGNITION OF PREGNANCY

• Sponsoring Institution: National Institute of Food and Agriculture
• Project Status: ACTIVE
• Funding Source: AFRI COMPETITIVE GRANT
• Reporting Frequency: Annual
• Accession No.: 1024969
• Grant No.: 2021-67015-33838
• Cumulative Award Amt.: $500,000.00
• Proposal No.: 2020-02777
• Project Start Date: Jul 1, 2021
• Project End Date: Jun 30, 2025
• Grant Year: 2021
• Program Code: [A1211]- Animal Health and Production and Animal Products: Animal Reproduction

Recipient Organization
OHIO STATE UNIVERSITY
1680 MADISON AVENUE
WOOSTER,OH 44691

Performing Department
Animal Science

Non Technical Summary
Pregnancy loss during the second month of pregnancy in cattle can vary from 4% to up 50% and has marked detrimental effects on reproductive efficiency and profitability of cattle operations. Maternal recognition of pregnancy (MRP) is the process by which the embryo within the uterus signals its presence to the mother to prevent regression of an ovarian endocrine gland, the corpus luteum (CL), and sustain progesterone (i.e., pro-gestation) production a critical hormone required to maintain pregnancy. The traditionally accepted period for MRP in cattle occurs during the first month after conception and mechanisms for this process are well understood but no longer exist after the first month of pregnancy. To prevent pregnancy losses after the first month of pregnancy, detailed knowledge is required of the mechanism responsible for maintenance of the CL - the pro-gestational structure. The proposed research will investigate the mechanisms involved in embryo-signaling to the maternal system to maintain the pro-gestational endocrine structure, the CL, after the first month of pregnancy. First, we will evaluate the changes in uterine blood flow when pregnancy is sustained or when abortion occurs and determine whether the amount of uterine blood flow has an effect on the function of the maternal pro-gestational gland. Second, we will evaluate whether maintenance of this gland during the second month of pregnancy requires an embryo specific signal. Third, we will evaluate the secretion pattern from the uterus of specific prostaglandins (PGF2α and PGE2) that are known to regulate functions of the pro-gestational gland when pregnancy is sustained or when abortion occurs. We anticipate that maintenance of the maternal pro-gestational gland and pregnancy can occur either by increasing uterine blood flow which results in decreased transfer of PGF2α, a hormone that induces CL regression, from the uterus to the ovary, thus preventing regression of this gland; and/or a conceptus derived substance being secreted subsequent to the first month of gestation that prevents regression of this pro-gestational gland even when PGF2α is present. Knowledge generated from conducting the proposed research will enhance understanding of mechanisms involved in maternal-fetal communication between the maternal pro-gestational gland (i.e., CL) and fetus during a period when there are significant pregnancy losses in cattle. Ultimately this knowledge can be utilized to develop new strategies to reduce pregnancy loss and thus improve reproductive efficiency and, therefore, production efficiency of cattle enterprises.

Animal Health Component

25%

Research Effort Categories

Basic

75%

Applied

25%

Developmental

(N/A)

Classification

Knowledge Area (KA)	Subject of Investigation (SOI)	Field of Science (FOS)	Percent
301	3310	1020	100%

Knowledge Area
301 - Reproductive Performance of Animals;

Subject Of Investigation
3310 - Beef cattle, live animal;

Field Of Science
1020 - Physiology;

Keywords

reproduction

cattle

corpus luteum

pregnancy loss

prostaglandin

uterine blood flow

Goals / Objectives
The long-term goals of this proposal are to: 1) Identify the mechanisms that allow for maintenance of the CL beyond the first month of pregnancy; 2) Determine the physiological differences between pregnancy loss due to conceptus demise or CL regression as these pertain to the conceptus - CL interaction; and 3) Reduce pregnancy loss that occurs as a result of premature CL regression in cattle by enhancing the physiological mechanisms involving conceptus - CL interactions and maintenance of the CL. The overall objective with the proposed research is to elucidate the physiological mechanisms that result in the maintenance or regression of the CL during the second month of gestation in cattle. Our central hypothesis is that the increase in uterovarian blood flow during the second month of gestation coincident with the development of the chorioallantoic placenta leading to reduced transport of uterine secreted PGF2α from the utero-ovarian vein to the ovarian artery and thus CL maintenance. Alternatively, the conceptus demise or inadequate conceptus development could prevent the increase in utero-ovarian blood flow resulting in luteolytic pulses of PGF2α reaching the CL and initiating luteolysis. Our specific objectives are: Objective 1. Establish whether the PGF2α secretion pattern and uterine blood flow is an important factor in maintenance of the CL during the second month of gestation in cattle; Objective 2. Determine whether the presence of a conceptus is necessary for maintenance of the CL during the second month of gestation; Objective 3. Gain a greater understanding of the contribution of utero-ovarian hemodynamics to pregnancy loss or maintenance of the CL during the second month of gestation; Objective 4. Determine the function of PGE as an agent for maintenance of the corpus luteum during the second month of gestation

Project Methods
The experimental approach will primarily utilize an induced pregnancy loss model in beef cattle that allows us to predict an evaluate the conceptus - CL interaction during the second month of pregnancy. Experiment 1: Temporal association between PGF2α secretion and changes in uterine blood flow after induction of pregnancy loss. Non-lactating beef cows (n = 40) will have their stage of the estrous cycle synchronized to allow for fixed time artificial insemination (FTAI) using a 5-day CO-Synch protocol. Cows will be randomized to undergo induced pregnancy loss (IPL; n = 10) at 35 days of gestation or remain as controls (n = 10). Induction of pregnancy loss consists of an intrauterine infusion of 120 ml of hypertonic saline placed in proximity of the embryo/fetus. All cows will be evaluated by B-mode, Color Doppler and Spectral Doppler ultrasonography twice daily starting at day 35 and until luteolysis is identified or the end of the experimental period at 70 days to asses CL size and vascularization, uterine artery perfusion, and conceptus viability. All cows will have jugular veins catheterized for determination of plasma PGFM (ELISA) at hourly intervals. Plasma P4 (RIA) and pregnancy specific protein B (PSPB; ELISA) will be assessed in plasma samples collected twice daily. Outcomes will be analyzed using a mixed model ANOVA with time included as a repeated measure. Experiment 2: Uterine PGF2α is responsible for CL regression after pregnancy loss. Non-lactating beef cows (n = 64) will have their stage of the estrous cycle synchronized to allow for FTAI. On day 35 pregnant (expected n = 32) cows will be treated to induce pregnancy loss (IPL). Cows will then be assigned to one of four treatments: Control (n = 8); Flunixin meglumine (FM; n = 8); Flunixin meglumine + early intrauterine PGF2α pulses (FM + PGF2α; n = 8); and Flunixin meglumine + late intrauterine PGF2α pulses (FM + PGF2α; n = 8). Cows in the FM group will receive 2.5 mg/kg of flunixin meglumine thrice daily starting on day 36 and until day 45 post FTAI. Intrauterine pulses of PGF2α will consist of four administrations of 0.25 mg of dinoprost tromethamine each at 6 h intervals administered on day 37 (early PGF2α group) or 45 (late PGF2α group). All cows will be evaluated using transrectal ultrasonography and plasma samples for P4 quantitation by RIA collected twice daily starting at day 35 and until luteolysis is identified. In addition, all cows will have jugular veins catheterized, to allow for collection of plasma samples at hourly intervals for determination of PGFM. Differences in the interval from IPL treatment to luteolysis will be assessed using ANOVA. Outcomes (progesterone, CL volume, uterine artery diameter, resistance index, etc.) will be analyzed using a mixed model ANOVA with time included as a repeated measure. Experiment 3: Induction of endometritis after pregnancy loss and its effect on the fate of the CL. Non-lactating beef cows (n = 60) will have their stage of the estrous cycle synchronized to allow for FTAI as described in Experiment 1. On day 35 pregnant (expected n = 30) cows will be assigned in a complete randomized design to one of three treatments as follows: Control (Pregnant control; n = 10); induced pregnancy loss (IPL, n = 10); or induced pregnancy loss + endometritis (IPL + EM; n = 10). Cows in the IPL + EM will be treated to induce pregnancy loss at day 35 and 48 h later endometritis will be induced by infusion of live pathogenic Escherichia coli and Trueperella pyogenes. All cows will be evaluated using transrectal ultrasonography twice daily starting at day 35 and until luteolysis is identified to assess CL size and vascularization, uterine artery perfusion, conceptus viability. Plasma samples, for P4 and PGEM quantitation, will be collected twice daily until luteolysis is identified or the end of the experimental period at day 90. Differences in the interval from IPL to luteolysis will be assessed using ANOVA.Experiment 4: Effect of reduced uterine blood on CL maintenance and pregnancy loss. Non-lactating beef cows (n = 40) will have their stage of the estrous cycle synchronized to allow for FTAI. On day 35 pregnant (expected n = 20) cows will be assigned in a complete randomized design to one of two treatments: Pregnant (control no further treatment) or Pregnant + vasoconstrictor (P+VD). Vasoconstriction to reduce blood flow in the utero-ovarian plexus will be achieved by intravenous administration of ergotamine tartrate until day 47 of gestation. Preliminary experiments will be performed to determine the appropriate dose of ergotamine tartrate to reduce blood flow in the utero-ovarian plexus. All cows will be evaluated using B-mode, Color Doppler and Spectral Doppler ultrasonography twice daily starting at day 35 to assess CL size and vascularization, uterine artery perfusion and conceptus viability. Plasma samples, for P4 and PSPB quantitation, will be collected twice daily from day 35 until pregnancy loss and luteolysis are identified. Differences in uterine artery perfusion characteristics, circulating P4 and PSPB will be analyzed using a mixed model ANOVA with time included as a repeated measure.Experiment 5: Effect of increased utero-ovarian blood flow after induced pregnancy on CL maintenance. Non-lactating beef cows (n = 32) will have their stage of the estrous cycle synchronized to allow for FTAI. On day pregnant (expected n = 16) cows will be assigned in a complete randomized design to one of two treatments (n = 8 per group) as follows: induced pregnancy loss (IPL) or induced pregnancy loss + vasodilator (IPL+VD). Vasodilation of the utero-ovarian plexus will be achieved by subcutaneous administration of sildenafil citrate thrice daily (100 mg/each) starting at day 37 of gestation and continuing until day 47. All cows will be evaluated by B-mode, Color Doppler and Spectral Doppler ultrasonography twice daily starting at day 35 and until luteolysis is identified to assess CL size and vascularization, uterine artery perfusion, and conceptus viability. Plasma samples, for P4 quantitation by RIA, will be collected twice daily starting at day 35 and until luteolysis is identified or the end of the experimental period. Timing of luteolysis will be compared between groups utilizing a two-sample t-test. Differences in uterine artery perfusion characteristics, circulating P4 will be analyzed using a mixed model ANOVA with time included as a repeated measure.Experiment 6: Effect of PGE administration after induced pregnancy loss on maintenance of the corpus luteum. Non-lactating beef cows (n = 32) will have their stage of the estrous cycle synchronized to allow for FTAI. On day 35 pregnant (expected n = 16) cows will be assigned in a complete randomized design to one of two treatments (n = 8 per group) as follows: induced pregnancy loss + vehicle (IPL control) or induced pregnancy loss + PGE1. Cows in the PGE1 group will receive intrauterine infusions of 2 mg of PGE1 diluted in 0.1 ml of DMSO every 6 h from day 37 until day. All cows will be evaluated using B-mode, Color Doppler and Spectral Doppler ultrasonography twice daily starting at day 35 and until luteolysis is identified to assess CL size and vascularization, uterine artery perfusion, conceptus viability. Plasma samples will be collected by coccygeal venipuncture twice daily starting at day 35 for P4 quantitation by RIA. Furthermore, plasma samples will be collected at 0 and 10 minutes after administration of treatments on day 40 for determination of PGEM by ELISA, to verify absorption of PGE1. Timing of luteolysis will be compared between groups utilizing a two-sample t-test. Differences in uterine artery perfusion characteristics, circulating P4 will be analyzed using a mixed model ANOVA with time included as a repeated measure.

Progress 07/01/23 to 06/30/24

Outputs
Target Audience:Scientists working in reproductive physiology,and graduate students in animal science. In addition, international stakeholders (veterinarians, and relevant industry enterprises) working with both beef and dairy cattle. Changes/Problems:When conducting experiment 2 of Objective 1 we encountered some unexpected obstacles related to the dose of flunixin meglumine as reported in the previous period. As a result, we utilized a lower dose and a different route of aministration (i.e., intrauterine). This approach was succesful in the inhibition ofprostaglandin F2 alpha secretion and resulted in corpus luteum maintenance.However, replacement of prostaglandin F2 alphaat a 0.25 mg dosage was not efficacious to induce luteolysis which negated our ablation and replacement approach.As a result we will evaluate the effect of different prostaglandin F2 alpha dosages after induced pregnancy loss and their ability to induce luteal regression. The additional experiments conducted under Objective 1 have resulted in a significant delay. Objective 3 of the proposed research hinges primarily on our ability to modulate (increase or decrease) uterine blood flow in order to determine the role of utero-ovarian perfusion in maintenance of the CL. During the previous reporting period we identified ana dequate dosage of sildenafil citrate that induces a detectable increase in utrine artery perfusion, however, thsi effect is short lived (2-3h)which negates our original experimental approach of repeated administrations. In the next reproting period we will evaluate the sue of intravaginal pressaries and/or osmotic pumps to allow prolonged delivery which is necesary for our objectives. Lastly, the pharmacological approach originally selected to reduce uterine blood flow was the useof ergotamine tartrate, surprisingly we have been unsuccesful in our attempts to source this compound. Multiple vendors have this product listed, however, they have been unable to deliver it to us, as a result we have decided to utilize an alternative product (L-NAME) as a vasoconstrictor and dose determination experiments will be conducted in the upcoming reproting period. What opportunities for training and professional development has the project provided?One graduate student completed their PhD degree, and their dissertation was based on the experiments proposed under Objetive1 of this project. In completion of the dissertation the student developed critical research skills, data analysis proficiencyas well as oral/written presentation skills.Another graduate student continues progressing towards her PhD degree which is primarily focused on this project. This student conducted the redesigned experiments required for Objective 2, and those reported for Objective 3. The studentdeveloped critical research skills as well as oral/written presentation skills.Durign this period the student was trainned in blood flow determination through ultrasonography and enzyme-linked immunoassays development and troubleshooting.In addition, 1 other graduate studentand 1 undergraduate student contributed towards the development of the work reported during this period and thus acquired valuable investigative skills. How have the results been disseminated to communities of interest?Results have been disseminated to different audiences through presentations at scientific meetings (NIFA/AFRI Project Director Meeting and NE-2227 USDA multistate project meetings), veterinary conferences(XXVI International Congress of the National Association of Spanish Specialists in Bovine Medicine)and through teaching to both undergraduate and graduate students. What do you plan to do during the next reporting period to accomplish the goals?The plans for the next reporting period are tocomplete data analysis of experiment 2 (Objective 1) and conduct an additional experiment to evaluate the effect of different dosages of PGF2α on CL maintenance after induced pregnancy loss. Objetive 4 hinges on the ability to modulate uterine artery blood flow, prelimianry findings durign the current reporting period indicate that use of sildenafil citrate to increase uterine artery blood flow is effective albeit shortlibed. Therefore, in the next reporting period we will evaluate alternative administration strategies (intravaginal pressaries and/or osmotic pumps)that couldallow for a sustained increase in uterinartery blood flow. Based on this results we will be able to address Experiment 4 (Objective 3) to determine whether increasing uterine perfusion after induced pregnancy losscan resultin CL maintenance. In addition, we will determine the dosage and route of administration of L-NAME that results in a sustain reduction of uterine blood flow. This dtermination will provide the opportunity to complete experiment 5 (Objective 3).

Impacts
What was accomplished under these goals? Experiment 2 (Objective 1) was designed to test the hypothesis that inhibition of PGF2α secretion will delay luteolysis after induced pregnancy loss while replacement of intrauterine PGF2α will result in luteolysis. Resultsrevealed thatsystemic administration of flunixin meglumine at a 1.65mg/kg dose was not sufficient to completelyinhibit uterinePGF2αsecretion, however, use of greater dosages was accompanied by severe toxicity. As a result, we evaluated the use of intrauterine administrationof flunixin meglumine as an alternative approach. We conducted a preliminary trial in cyclic cows to test the most appropriate dosage and observed that intrauterine administrationof 240 mgof flunixin meglumine was effective in inhibiting PGF secretion and preventing CL regression without adverse effects. Next, we proceededto conduct experiment 2 again using the intrauterine dosage of240 mgof flunixin meglumine. Pregnant beef cows had pregnancy loss induced at day 35 of gestation and were assigned to receive flunixin meglumine (240 mg intrauterine/8h), flunixin meglumine + PGF2α (0.25 mg/8 h four intrauterine administrations) or remain untreated (Control). Sample collection has been completed and data analysis is currently underway. Preliminary dataindicates that inhibition of PGF2α effectively prevents CL regression, albeit PGF replacement at a 0.25mg dosage appears insufficient to induce luteolysis after induced pregnancy loss. Experiments designed to address objective 3, were initiated. Preliminary experiments were conducted in cyclic cows to determine the most appropriate dosage and route of administration (subcutaneous or intrauterine) for sildenafil citrate. We observed that 100 mg of sildenafil citrate produced an increase of nearly 50% in uterine artery perfusion, however, the effect was short-lived (2-3 h). This finding represents a challenge for the completion of Experiment 4 (see Problems).

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2024 Citation: A. Garcia Guerra, B. Duran, J. C. L. Motta, R. V. Sala, M. C. Wiltbank. Perdidas gestacionales: bases fisiologicas y estrategias para reducirlas. (Translation: Pregnancy loss: physiological bases and mitigating strategies). Proceedings of the XXVI Congreso Internacional Anembe de Medicina Bovina (XXVI International Congress of Bovine Medicine Anembe) 2024, April 24 - 26, C�rdoba, Spain, Pages 184-199.
• Type: Theses/Dissertations Status: Accepted Year Published: 2024 Citation: Duran B. D. Development of an Induced Pregnancy Loss Model to Assess the Mechanism of Corpus Luteum Maintenance After Maternal Recognition of Pregnancy in Cattle. 2024. Ohio State University, Doctoral Dissertation. OhioLINK Electronic Theses and Dissertations Center

Progress 07/01/22 to 06/30/23

Outputs
Target Audience:Scientists working inreproductive physiology, undergraduate and graduate students in animal science and veterinary medicine. In addition, local, regional and international stakeholders (veterinarians, producers, and relevant industry enterprises) working withboth beef and dairy cattle. Changes/Problems:When conducting experiment 2 of Objective 1 we encountered some unexpected obstacles related to the dose of flunixin meglumineas reported in the previous period. As a result, we utilized a lower dose, however, this was not sufficient to inhibit prostaglandin secretion and thus prevent corpus luteum regression. Through collaborative efforts with a colleague at anotehr institution, we have determined that intrauterine administration will allow us to achieve the desired inhibitory effect, and as a result, we are planning to repeat experiment 2 (Objective 1) in the upcoming reporting period.In addition, we encountered some difficulties with the in-house assay to determine prostaglandin F2 alpha metabolite related to the primary antibody provided by a collaborating institution. We have now identified the issue and proceed to correct it which has allowed us to resume sample analysis of samples collected for objective 1 and 2. What opportunities for training and professional development has the project provided?One graduate student developed critical research skills as well as oral/written presentation skills as a result of this project. He is currently preparing the outcomes of Objective 1 for publication and completing the dissertation for completion of the PhD degree. Anothergraduate studentcontinues progressing towards her PhD degree which is primarily focused on this project. This student conducted the experiments required for Objective 2. In addition, 3 other graduate students and 1 post-doc contributed towards the development of the work reported during this period and thus acquired valuable investigative skills. How have the results been disseminated to communities of interest?Results have been disseminated to different audiences through presentations at scientific meetings (Society for the Study of Reproduction, NIFA/AFRI Director Meeting), USDA multistate project meetings (NE-2227) and through teaching to both undergraduate and graduate students. What do you plan to do during the next reporting period to accomplish the goals?The plans for the next reporting period are to: 1) complete the sample analysis for Experiment 1 (Objective 1) and write a manuscript for publication, 2) repeat Experiment 2 (Objective 1) based on the challenges encountered (see Problems); 3) complete sample analysis for Objective 2, and 3) initiate experiments required to completeObjective 3.

Impacts
What was accomplished under these goals? Sample analysis for experiment 2 of Objective 1 was completed, and final statistical analysis is currently underway. Experiment 2 was designed to test the hypothesis that inhibition of PGF2α secretion will delay luteolysis after induced pregnancy loss while replacement of intrauterine PGF2α will result in luteolysis. Preliminary sample analysis revealed that systemic administration of flunixin meglumine at a 1.65mg/kg dose was not sufficient to inhibit uterine prostaglandin f2alpha secretion. Data collection for the experimentdesigned to address Objective 2 wascompleted, sample and statistical analyses are underway. The experiment conducted was designed to test the hypothesisthat induction of endometritis would prevent luteolysis and extend the CL lifespan in cows undergoing induced pregnancy loss. Preliminary results indicate thatthe occurrence of endometritis after induced pregnancy loss did not affect the lifespan of the CL after pregnancy loss during the second month of pregnancy in cattle.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2023 Citation: N. P. Folchini, B. J. Duran, C. Rykaczewski, A. E. Crist, M. Saad, A. C. Carranza-Martin, J. C. L. Motta, D. F. Mollenkopf, M. L. Mussard, A. Garcia-Guerra. Induction of endometritis after pregnancy loss during the second month of gestation in cattle and its effect on the fate of the corpus luteum Proceedings of the 56th Annual Meeting of the Society for the Study of Reproduction 2023, July 11th  14th, Ottawa, Canada, Page 386.

Progress 07/01/21 to 06/30/22

Outputs
Target Audience:Scientists working in similar areas of reproductive physiology, undergraduate and graduate students in animal science and veterinary medicine. In addition,local, regional and international stakeholders (veterinarians, producers, and relevant industry enterprises) working in both beef and dairy cattle. Changes/Problems:When conducting experiment 2 of Objective 1 we encountered some unexpected obstacles. This experiment hinges on the use of flunixin meglumine to inhibitPGF2αsecretion. We initially utilized a dose that was reported as effective in several peer-reviewed publications. However, we encountered that the use of this dose for a prolonged period of time as needed for this experiment resulted in toxicity. As a result, the experiment was suspended. We then utilized a reduced dose of flunixin meglumine (75% of that reported in the literature), this allowed us to complete the experiment and avoid toxicity. However, we have yet to verify whetherPGF2αsecretion inhibition was in fact accomplished. This will be accomplished in the next reporting period and based on the results we will assess the direction for the remaining experiments or the need to repeat this critical experiment using a different inhibition strategy. What opportunities for training and professional development has the project provided?One graduate student (Ben Duran) has developed critical research skills (sample collection, hormonal determination)as well as oral/written presentation skills as a result of this project. He completed his candidacy examination during this last reporting period and is currently completing sample analysis of the project completed and writing the corresponding manuscripts. One other graduate student (Natalia Picoli) began working towards her PhD degree which will be primarily focused on this project. In addition, 3 other graduate students and 1 post-doc contributed towards the development of the work reported during this period and thus acquired valuable investigative skills. How have the results been disseminated to communities of interest?Results have been disseminated to differentaudiences through presentation at scientific meetings (Society for the Study of Reproduction, NIFA/AFRI Director Meeting), USDA multistate project meetings (NE-1727) and through teaching to both undergraduate and graduate students. What do you plan to do during the next reporting period to accomplish the goals?The plans for the next reporting period are to: 1) complete experiments included in Objective 2; and 2) address some challenged encountered during Experiment 2 of Objective 1 to better define the role ofPGF2αsecretion (see Problems).

Impacts
What was accomplished under these goals? Experiments designed to address Objective 1 were completed. In experiment 1, wetested the hypothesis that luteolysis after pregnancy lossis temporally associated with a decrease in ipsilateral uterine artery vascular perfusion. Pregnant beef cows wereassigned to undergo induced pregnancy loss (PIL) at day 35 of gestationor remain untreated.Subsequently,blood samples were collected for quantification of plasma progesterone (P4)until luteolysis was identified and ipsilateral uterine artery resistance index (RI) was evaluated daily using spectral-doppler ultrasonography and vascular perfusion index was calculated. In addition, cows were fitted with indwelling jugular catheters and samples were collected bihourly to determinecirculating concentrations of PGFM. Field work and samples collection has been completedand vascular perfusion data and P4 data has been analyzed. Preliminary analysis indicate that vascular perfusion index is reduced by24% in cows undergoing pregnancy loss and this reduction is temporally associated with luteolysis. In experiment 2 we tested thehypothesis that inhibition of PGF2αsecretion will delay luteolysis after induced pregnancy loss while replacement of intrauterine PGF2α will result in luteolysis. Pregnant beef cows had pregnancy loss induced at day 35 of gestation and wereassigned to receive flunixin meglumine (FM, to inhibit PGF2αsecretion), flunixin meglumine + PGF2α or remain untreated(Control).Blood samples were collected twice daily for P4quantification and determination of the onset of luteolysis, and bihourly samples for PGFM determination were collected during a 24 h period.Field work and samplecollection has been completedand P4 data has been analyzed. This experiment was conducted twice using different conditions due to some difficulties encountered (see Problems).Preliminary analysis indicates that inhibition ofPGF2αsecretion did not preventluteolysis, however, luteolysis was delayed after administration of flunixin meglumine.

Publications

• Type: Conference Papers and Presentations Status: Published Year Published: 2021 Citation: B. J. Duran, F. L. V. Pinaffi, J. C. L. Motta, C. Hayden, A. E. Crist, C. Rykaczewski, S. Wellert, E. Rojas-Canadas, M. L. Mussard, A. Garc�a-Guerra. 2021. Corpus luteum regression after induced pregnancy loss in cattle is preceded by a reduction in uterine artery vascular perfusion. Abstract P136. Proceedings of the 54th Annual Meeting of the Society for the Study of Reproduction 2021
• Type: Conference Papers and Presentations Status: Published Year Published: 2022 Citation: B. J. Duran, A. E. Crist, J. C. L. Motta, C. Rykaczewski, C. Hayden, M. Saad, A. Carranza-Martin, M. L. Mussard, A. Garc�a-Guerra. 2021. Role of prostaglandin F2? in corpus luteum regression after conceptus demise in cattle. Abstract P121. Proceedings of the 55th Annual Meeting of the Society for the Study of Reproduction 2022, July 26-29, Spokane, WA.