Changes in intrauterine pressure after oxytocin administration in reproductively normal mares and in those with a delay in uterine clearance

Intrauterine pressure was measured in 4 reproductively normal mares and 4 mares with delay in uterine clearance after administration of oxytocin to determine if intrauterine pressure varied between dosage and group. Changes in intrauterine pressure were measured during estrus, when a follicle was > or =35 mm, using a Millar "Mikro-tip" catheter that had 3 discrete pressure sensors/channels. Mares received 4 different treatments of 10, 5, 2.5 or 0 IU (vehicle) of oxytocin. The protocol for each treatment consisted of a 10-min baseline recording, administration of treatment and measurement of changes in intrauterine pressure for 65 min. After administration of the first two treatments, mares were rested for 2 h and the protocol repeated for the remaining 2 treatments. Changes in intrauterine pressure were measured on a physiograph and stored in a computer. The results were analyzed by 4x4 Latin Square Design analysis of variance (ANOVA) using the GLM procedure of the Statistical Analysis System. The ANOVA detected a main effect of treatment (P<0.01) and mare (nested within group; P<0.01) but no effect of channels, group or treatment-by-group interaction. There was a dose-dependent increase in uterine activity in both normal mares and those with delayed uterine clearance. A dose of 10 IU of oxytocin induced a larger number of uterine contractions (5.67+/-0.06) for a longer time (24.09+/-1.18 min) than the 5 IU (4.16+/-0.06 contractions and 16.31+/-1.18; P<0.01 min) or 2.5 IU dose (4.08+/-0.06 contractions and 17.61+/-1.18 min). The first intrauterine wave occurred most often near the tip of the horn in 10 of 12 recordings in normal mares and in 8 of 12 recordings in mares with delayed uterine clearance. It was then propagated from the middle of the horn to the uterine body just cranial to the cervix. There was no pattern of propagation for subsequent intrauterine pressure waves. We conclude that the difference in spontaneous clearance of the uterus between the 2 groups is not reflected in their response to exogenous oxytocin as determined by changes in intrauterine pressure.     

Aberrations in uterine contractile patterns in mares with delayed uterine clearance after administration of detomidine and oxytocin

An experiment was conducted to determine whether the uterotonic effects of oxytocin, a drug used to treat mares that have a delay in uterine clearance were affected by the sedative detomidine (an alpha2-agonist), a drug used to treat fractious mares. An additional objective was to identify propagation patterns of uterine contractions and determine whether these patterns differed between normal mares and mares with delayed uterine clearance (DUC). Intrauterine pressure was measured in five reproductively normal mares and four mares with DUC during estrus using an 8-F Milar catheter with two discrete pressure sensors. Mares received one of three treatments in random order: detomidine (0.001 mg/kg; i.v.); detomidine followed in 10 min by oxytocin (10 IU; i.v.); and saline (0.9% NaCl 0.5 ml; i.v.) followed in 10 min by oxytocin. All treatments induced waves of contractions; however, only three mares with DUC exhibited contractions after administration of detomidine. Normal mares experienced more uterine contractions (P < 0.01) that tended to last longer (P < 0.06), and were of greater intensity (P < 0.04) than mares with delayed clearance. Administration of detomidine before oxytocin increased the number of contractions (P < 0.02) and increased the maximum intrauterine pressure in the uterine horn (P < 0.05) in normal mares as compared to response after administration of saline and oxytocin. Detomidine had no effect in mares with delayed clearance. All mares had more propagating than non-propagating uterine contractions (74 +/- 8 versus 25 +/- 8%, respectively). Normal mares exhibited a normal propagation pattern more frequently (P < 0.0001) than mares with DUC. Simultaneous (P < 0.05) and inverted (P < 0.03) contractions occurred more frequently in mares with DUC. Administration of detomidine increased the number (P < 0.01), and tended to increase the percentage (P < 0.07) of normal propagating uterine contractions in normal mares, but did not affect propagation patterns in mares with DUC. In conclusion, detomidine augmented the uterotonic effect of oxytocin in normal mares but not in mares with DUC. Data suggest that mares with DUC have a defect in myoelectrical signaling and a decrease in the contractile strength of the uterine muscle.     

Effects of prostaglandin F2α, cloprostenol and fenprostalene on uterine clearance of radiocolloid in the mare

Uterine clearance of radiocolloid was measured by scintigraphy in 5 reproductively normal mares and in 4 mares exhibiting a delay in uterine clearance (DUC) after administration of PGF_2α, cloprostenol or fenprostalene. Scintigraphy studies were performed on the second or third day of estrus during 3 consecutive estrous cycles. Drugs, PGF_2α (5 mg IM), cloprostenol (CLO; 2mg IM) or fenprostalene (FEN; 250 μg subcutaneously) were given in random order, with only 1 drug given each estrus. Treatment response curves were generated, and the effect of each drug on uterine clearance of radiocolloid was compared to the clearance of radiocolloid when no drug was given and between treatments. In reproductively normal mares, CLO and PGF caused a rapid clearance of radiocolloid within 60 min (P < 0.01), with <25% of the initial dose of radiocolloid (% IDR) remaining by 120 min. Mean percentage of IDR at 120 min when no drug was given was 39% ± 4. Response of reproductively normal mares to FEN varied, with 3 mares clearing > 85% and 2 mares clearing <35%. In mares exhibiting DUC, all 3 drugs (CLO, PGF and FEN) caused rapid clearance of radiocolloid from the uterus by 60 min (P < 0.0001). Mares cleared significantly more colloid after treatment with CLO at 60 and 120 min than after PGF (P < 0.001). In conclusion, CLO appears to be the best drug of the 3 tested for stimulating clearance of intrauterine fluid since variation in response was observed following treatment with PGF and FEN.     

Differences in uterine position of reproductively normal mares and those with delayed uterine clearance detected by scintigraphy

The position of the uterus within the abdomen may affect a mare's ability to rapidly clear the uterine lumen of contamination. In this study, the position of the uterus was determined from left and right lateral flank scintigrams taken 1 and 2 h after intrauterine infusion of radiocolloid. Scintigraphy was performed during estrus in 44 mares, 24 were reproductively normal and 20 exhibited a delay in uterine clearance. Reproductively normal mares were nulliparous (n = 14) or pluriparous (n = 10), 3 to 21 yr of age, had no history of persistent uterine infections and cleared > 50% of a radiocolloid within 2 h of infusion into the uterus. Mares that exhibited a delay in uterine clearance were pluriparous (n = 18) or nulliparous (n = 2), 12 to 24 yr of age, had a history of endometritis and cleared < 30% of a radiocolloid within 2 h. The angle between the caudal-ventral aspect of the uterine image and cervix relative to horizontal as visualized on the scintigram was measured with a protractor. Results were analyzed by the General Linear Model System. The uterine-cervical angle relative to horizontal was more ventral in mares with delay in uterine clearance and was more horizontal in reproductively normal mares (mean +/- SEM-111.6 +/- 3.6 for delay in uterine clearance mares; 147.6 +/- 3.9 for reproductively normal mares; P < 0.0001). The mean angle for reproductively normal, pluriparous mares was steeper than that for nulliparous mares (141.1 +/- 2.9, 152.3 +/- 2.44 respectively; P = 0.004). There were no differences in angles between left and right lateral views within individuals. We conclude that a uterus that tilts ventrally in relation to the pelvic brim may contribute to the inability of delay in uterine clearance mares to rapidly clear their uterine lumen of contamination. Parity may contribute to the more ventral orientation of the uterus.     

Spontaneous and oxytocin-induced uterine motility in cyclic and postpartum mares

Intrauterine pressure was measured in three cyclic and two postpartum mares. Pressure was recorded using a catheter tip pressure transducer. The transducer was passed transcervically into the uterus.. In cyclic mares recordings were started on Day 1 of estrus and continued daily until ovulation as well as on Days 1 and 8 of diestrus. In postpartum mares recordings were started within 48 h after foaling and continued until the mares ovulated. The intrauterine pressure changes in postpartum mares was also recorded on Days 1 and 8 of diestrus. Spontaneous uterine contractions were recorded in cyclic mares for 30 min and in postpartum mares for 10 min. Induced uterine motilities were recorded for 30 min in both groups after the administration of oxytocin (40 USP, i.v.). Total area under the contraction curve in a 10-min period was used as a uterine motility quantitating unit. All mares demonstrated uterine contractions during estrus and diestrus. All mares demonstrated significant responses to oxytocin during estrus and diestrus. It appears that estrogen priming is not necessary for a significant uterine response to oxytocin.     

Mares with delayed uterine clearance have an intrinsic defect in myometrial function

Persistent, postmating endometritis affects approximately 15% of mares and results in reduced fertility and sizable economic losses to the horse-breeding industry. Mares that are susceptible to postmating endometritis have delayed uterine clearance associated with reduced uterine contractility. Unfortunately, the mechanism for reduced uterine contractility remains an enigma. The present study examined the hypothesis that mares with delayed uterine clearance have an intrinsic contractile defect of the myometrium. Myometrial contractility was evaluated in vitro by measuring isometric tension generated by longitudinal and circular uterine muscle strips in response to KCl, oxytocin, and prostaglandin F(2alpha) (PGF(2alpha)) for young nulliparous mares, older reproductively normal mares, and older mares with delayed uterine clearance. In addition, intracellular Ca(2+) regulation was evaluated using laser cytometry to measure oxytocin-stimulated intracellular Ca(2+) transients of myometrial cells loaded with a Ca(2+)-sensitive fluorescent dye, fluo-4. For all contractile agonists, myometrium from mares with delayed uterine clearance failed to generate as much tension as myometrium from older normal mares. Oxytocin-stimulated intracellular Ca(2+) transients were similar for myometrial cells from mares with delayed uterine clearance and from older normal mares, suggesting that the contractile defect did not result from altered regulation of intracellular Ca(2+) concentration. Furthermore, no apparent age-dependent decline was observed in myometrial contractility; KCl-depolarized and oxytocin-stimulated longitudinal myometrium from young normal mares and older normal mares generated similar responses. However, circular myometrium from young normal mares failed to generate as much tension as myometrium from older normal mares when stimulated with oxytocin or PGF(2alpha), suggesting possible age-related alterations in receptor-second messenger signaling mechanisms downstream of intracellular Ca(2+) release. In summary, for mares with delayed uterine clearance, an intrinsic contractile defect of the myometrium may contribute to reduced uterine contractility following breeding.     

Effect of dose and day of treatment on uterine response to oxytocin in mares

To determine the effect of dose and day of oxytocin treatment on intrauterine pressure, 6 normal mares were treated with 10 or 25 IU oxytocin 2 days before ovulation, on the day of ovulation and 2 days after ovulation. Intrauterine pressure (IUP) was measured using micro-tip-catheters (one placed intrauterine, a second and third serving as reference sensors in the vagina and external to the mare) and transmitted by telemetry for 30 min to establish a baseline before saline was administered, iv, and for an additional 30 min after saline administration. Oxytocin was then given, iv, and IUP was recorded for 60 min. No change in IUP was observed after saline injection. The administration of both 10 (n=16) and 25 (n=10) IU oxytocin induced a response (P<0.01). The intensity of response depended on the day of administration (P<0.01) and the dose of oxytocin (P<0.001). The variation of response was significantly greater after 10 IU oxytocin (CV 15.78%) compared with 25 IU oxytocin (CV 6.42%). The uterine response was greatest on Day 2 prior to ovulation and lowest on Day 2 after ovulation. The response was negatively correlated to increasing plasma progesterone (10 IU oxytocin: r = -0.435, 25 IU oxytocin: r = -0.265). There was no correlation between the uterine response and plasma estradiol-17beta concentration (P<0.01). In conclusion the results of this study show that oxytocin administration to mares before ovulation provides a greater response than after ovulation. A decline in the intensity of response after ovulation can be compensated for with a higher dose of oxytocin. Furthermore, the use of the multiple catheter technique is an effective method for assessing changes in uterine pressure.     

Release of oxytocin and prostaglandin f(2alpha) around teasing, natural service and associated events in the mare

Mating has been shown in many species to provoke the release of oxytocin (OT). In our study, various stimuli were applied to mares to study release of OT and prostaglandin F(2alpha) (PGF(2alpha)) associated with mating. Blood samples were collected from mares around the time of teasing both in oestrus and dioestrus and at mating. For comparison, blood samples were also collected at the time of manual manipulation of the genital tract and after intrauterine infusion of 500 ml phosphate buffered saline (PBS). Additional samples were collected 16 to 18 h after mating. Mating caused a significant increase in OT in all mares and teasing caused a significant OT response in 6 of 10 oestrous and 3 of 5 dioestrous mares. However, mating and teasing had no significant effect on concentrations of 15-keto-13,14-dihydro-PGF(2alpha) (PGFM). Manual manipulation of the clitoris, vagina and cervix caused significant OT release in all mares and intrauterine infusion of 500 ml PBS caused significant OT release in three of the five mares. However, only one mare had a significant PGF(2alpha) response during manual manipulation and only one responded positively to intrauterine infusion of 500 ml PBS. We concluded that events around mating, including stimulation of the genital tract and uterine distension, often caused an increase in circulating concentrations of OT but only rarely in PGFM.     

Effect of oxytocin and flunixin meglumine on uterine response to insemination in mares

The most probable reason for persistent postbreeding endometritis in mares is weak myometrial contractility. The influence of oxytocin (OT; an ecbolic agent) and flunixin meglumine (FLU; a prostaglandin inhibitor serving as a model for mares with decreased uterine contractility) on uterine response to artificial insemination (AI) was studied in mares with no history of reproductive failure. The mares were treated intravenously with 10 mL saline (Group C, n = 10) or 0.01 IU/kg OT (Group OT, n = 10) 2, 4, 8, and 25 h after AI. Group FLU (n = 11) was treated with 1.1 mg/kg FLU 2 h after AI and with saline thereafter. The mares received the same treatments in the first and third cycles but were sampled either at 8 or 25 h. The amount of intrauterine fluid (IUF) and edema and the number of uterine contractions were recorded before AI and 10 min after the treatments using transrectal ultrasonography. At 8 h after AI, the mares were treated with human chorionic gonadotropin, and, after 8-h or 25-h scans, a 500-mL uterine lavage and a biopsy were performed. Ovulation was confirmed at 48 h and pregnancy 14 to 17 d after AI. No manipulations were done during the second estrus. At 8 h after AI, Group FLU had more polymorphonuclear leukocytes (PMNs) in the uterine lavage fluid than did Group OT (P < 0.05), but uterine contractions did not differ significantly. At 25 h, the PMN concentrations were low in all groups. Group OT rarely showed IUF. The uterine biopsy specimens of Group FLU showed less inflammation of the stroma but more PMNs in the uterine lumen 8 h after AI than that of the control group (P < 0.05). The pregnancy rates did not differ between the groups (63% C, 53% OT, and 50% FLU). Oxytocin rapidly and effectively removed IUF and PMNs after AI and thereby shortened the duration of postbreeding inflammation.     

Changes in uterine secretion of prostaglandin F2 alpha and luteal secretion of progesterone in response to oxytocin during the porcine estrous cycle.

The purpose of this experiment was to determine whether the ability of oxytocin to stimulate uterine secretion of prostaglandin F2 alpha (PGF2 alpha) and luteal secretion of progesterone changes during the porcine estrous cycle. Nineteen multiparous sows were observed for estrus. After one estrous cycle of normal length, sows were assigned randomly to receive an injection of oxytocin (30 IU, i.v.) in the EARLY (Days 4-6; n = 6), MID (Days 9-11; n = 7), or LATE (Day 15; n = 6) stage of the estrous cycle. Concentrations of 13, 14-dihydro-15-keto-PGF2 alpha (PGFM) and progesterone were determined in jugular venous serum samples collected at -60, -45, -30, -15, 0, 2, 5, 10, 15, 30, 45, 60, 90, and 120 min after injection of oxytocin. The magnitudes of the PGFM and progesterone responses and the area under the respective response curves (AUC) were calculated for each sow. Concentrations of PGFM did not change in response to oxytocin administered during the EARLY or MID portions of the estrous cycle. Concentrations increased rapidly in 4 of 6 sows that received oxytocin LATE in the estrous cycle. Both magnitude and AUC were greater LATE in the estrous cycle than at either EARLY or MID cycle (p less than 0.05). Thus, uterine secretory responsiveness to oxytocin develops between Days 11 and 15 postestrus in the sow. For progesterone, a transient increase was observed immediately following injection of oxytocin at MID cycle (p less than 0.05), but not at the other times examined. Therefore, oxytocin appears to be capable of stimulating secretion of progesterone from the functionally mature corpus luteum.     

Effect of PGE2 on uterine contractility and tone in mares

A technique for transvaginal, ultrasound-guided intrauterine injection was developed. After preliminary study using different approaches, the procedure was successful in 24 of 25 (96%) mares, based on detecting fluid in the uterine lumen during and after the injection. The technique was used to study the effect of PGE2, reportedly produced by the embryonic vesicle, on uterine contractility on Day 12 (Day 0 = ovulation). Uterine contractility was scored (1 = minimal, 4 = maximal) every 10 min for 1 h and every 30 min for the next hour by a continuous 1-min ultrasound examination of a longitudinal section of the uterine body without knowledge of group. In Experiment 1, the main effect of group (1-mL vehicle, n = 6; 0.25 microgram PGE2, n = 7) tended to be significant (P < 0.09), and the effect of time was significant (P < 0.008). The mean score was higher for the PGE2 group (2.0 +/- 0.1) than for the vehicle group (1.7 +/- 0.1). An increase in contractility occurred between 0 and 5 min in the vehicle group (P < 0.0004) and between 0 and 10 min in the PGE2 group (P < 0.04). In Experiment 2, there was a tendency (P < 0.08) for effect of group (control without injection, n = 6; 1-mL vehicle, n = 6; 0.025 microgram PGE2, n = 6). The PGE2 group (2.0 +/- 0.1) was different from the vehicle group (1.6 +/- 0.1) and the control group (1.6 +/- 0.1). An increase in contractility occurred between 0 and 20 min in the PGE2 group, and the changes were not significant in the other groups. However, scores were higher in the PGE2 group before treatment, and there were no significant effects when data were converted to percentage changes. The results for an effect of intrauterine treatment of PGE2 on uterine contractility are considered uncertain because of the transient increase in contractility from vehicle injections in Experiment 1 and the higher score in the PGE2 group before treatment, with no significant differences in percentages in Experiment 2. Indirectly, however, an effect of PGE2 was suggested by a shorter (P < 0.05) period of detectability of intrauterine fluid in the PGE2 groups (21 +/- 31 min) than in the vehicle groups (50 +/- 42 min). The shorter period was attributable to greater dispersion of the fluid as a result of increased contractility. In Experiment 3, PGE2 (10 mg, n = 5) and vehicle (4 mL, n = 5) were given intravenously. In addition to uterine contractility, uterine tone was scored (1 = minimal, 4 = maximal) by transrectal digital compression. The main effect of group was significant (P < 0.03) for uterine contractility score, which increased between 0 and 20 min after PGE2 injection. The time effect and interaction were highly significant (P < 0.0001) for uterine tone score, and tone increased in the PGE2 group between 0 and 20 min after injection. The results indicated that PGE2 should be considered as a potential stimulator of both uterine contractions and uterine tone during the time of embryo mobility in mares.     

Effect of insemination dose and site on uterine inflammatory response of mares

It is unclear whether AI of mares deep into the uterine horn causes more or less inflammation of the endometrium than conventional AI. Thus, we compared uterine inflammatory reactions of mares inseminated with two different doses of frozen-thawed semen into the tip of the uterine horn (UH) ipsilateral to the preovulatory follicle with those of mares inseminated into the uterine body (UB). Thirty-two mares were assigned to one of four groups (eight mares/group): UB20=AI into UB, 20 x 10(6)sperm/0.5 mL; UB200=AI into UB, 200 x 10(6)sperm/0.5 mL; UH20=AI into UH, 20 x 10(6)sperm/0.5 mL; UH200=AI into UH, 200 x 10(6)sperm/0.5 mL, and inseminated 24 h after hCG administration. Before and 24 h after AI, they were examined with ultrasonography for the presence of intrauterine fluid. At 24 h, uterine fluid samples were obtained first by absorbing fluid into a tampon and then by uterine lavage. Uterine fluid was examined for polymorphonuclear leukocytes (PMN) and bacteriology, and frozen for lysozyme and TIC (trypsin-inhibitor capacity) assays. Only three mares conceived, one in each of the following groups: UB200, UH20, and UH200. Mares in the UH20 group accumulated less intrauterine fluid (p<0.05) than those in the other groups, which had similar amounts. No significant differences in PMN numbers were detected in either tampon or lavage fluid. Enzyme levels between groups did not differ statistically, except for TIC, which was lowest in the UH200 group. Thus, deep uterine horn AI caused no greater inflammation or irritation than uterine body AI in normal mares 24 h after insemination.     

Effect on fertility of human chorionic gonadotrophin and uterine lavage with oxytocin performed after mating in Arabian barren mares

The objective of the present study was to evaluate the beneficial effect of hCG injected immediately after mating in Arabian barren mares treated with uterine lavage and oxytocin. Arabian barren mares (n = 36) with PMIE were subjected to detailed clinical examinations including palpation per rectum, vaginoscopy, and cytological examination. After mating the 36 mares were randomly divided into four groups. The mares in group 1 (n = 10) were immediately after breeding injected with hCG 3000 IU IM. Uterine lavage with 1 L of N-saline containing 4 million IU of crystalline penicillin and 4 g of streptomycin sulphate was performed 4 h after breeding. Then mares received two injections of oxytocin 40 IU IM 2 h apart after 6 h of mating. Mares in group 2 (n = 10) treated with uterine lavage and oxytocin as group 1. While mares in group 3 (n = 10) received uterine lavage only. A control group (n = 6) as group 4 did not received any treatment. The results of clinical examination indicated that 69.4% of PMIE mares were harboring severe endometritis and 30.6% with a moderate form of endometritis. Significant (P < 0.01) increase in lymphocytes were founded in barren mares included in this study. Higher pregnancy rate (P < 0.01) was founded in Arabian barren mares 80% injected with hCG immediately after breeding and uterine lavage and oxytocin. No significant difference was found in mares received uterine lavage and oxytocin and uterine lavage only. In a conclusion, administration of hCG immediately after mating and intrauterine lavage containing antibiotics performed 4 h and two injections of oxytocin 40 IU IM 2 h apart after 6 h of mating had improved fertility of Arabian barren mares.     

Effect of intrauterine treatment with prostaglandin E2 prior to insemination of mares in the uterine horn or body

Two trials were conducted to investigate the effects of intrauterine infusion of PGE2 and uterine horn insemination on pregnancy rates in mares achieved by breeding with a suboptimal number of normal spermatozoa. Estrus was synchronized and mares were teased daily with a stallion to detect estrus. Mares in estrus were examined by transrectal palpation and ultrasonography to monitor follicular status. On the first day a 35-mm diameter follicle was present, hCG (1500 IU, iv) was administered and the mares were bred the next day. Mares (Trial 1, n = 34; Trial 2, n = 28) were inseminated with 25 million total spermatozoa from either a stallion with good semen quality (Trial 1) or poor semen quality (Trial 2). In each trial, mares were assigned to 1 of 4 treatment groups as follows: Group PGE-HI - infusion of 0.25 mg PGE2 into the proximal end of the uterine horn ipsilateral to the dominant follicle 2 h prior to insemination in the proximal end of the same uterine horn; Group PGE-BI - infusion of 0.25 mg PGE2 into the proximal end of the uterine horn ipsilateral to the dominant follicle 2 h prior to insemination in the uterine body; Group SAL-HI - infusion of 1 mL sterile saline into the proximal end of the uterine horn ipsilateral to the dominant follicle 2 h prior to insemination in the proximal end of the same uterine horn; or Group SAL-BI - infusion of 1 mL sterile saline into the proximal end of the uterine horn ipsilateral to the dominant follicle 2 h prior to insemination in the uterine body. After breeding, mares were examined daily by transrectal ultrasonography to confirm ovulation, and were re-examined 14 to 16 d after ovulation for pregnancy status. Data were analyzed by Chi-square. Overall pregnancy rates were 59% for stallion 1 and 29% for stallion 2. Group pregnancy rates did not differ for mares bred by either stallion (P > 0.10). Pregnancy rates were not altered by horn insemination for either stallion (P > 0.10). Intrauterine infusion of PGE2 improved pregnancy rate in mares bred by the stallion with good quality semen (P < 0.05), but did not alter pregnancy rate in mares bred by the stallion with poor quality semen (P > 0.10). Further research is warranted to determine if intrauterine infusion of PGE2 will enhance spermatozoal colonization of the oviduct and pregnancy rates in mares, and if PGE-treatment will improve pregnancy rates achieved by subfertile stallions.     

Effect of estrogen formulation and its site of deposition on serum PGFM concentrations, uterine contractility, and time of ovulation in artificially inseminated weaned sows

At the time of artificial insemination, 48 mixed parity sows were assigned by parity to receive 25 microg estradiol-17beta either in oil deposited onto the vaginal mucosa (E-oil), or dissolved in extended semen (E-semen), or received no estrogen and served as controls. All sows were inseminated transcervically 24 h after detection of estrus. The time of ovulation was determined in 15 sows per treatment by transrectal ultrasonography. Concentrations of prostaglandin F2alpha metabolite (PGFM) were determined in blood samples obtained from eight sows per treatment at 1 h intervals from 1 h pre-treatment until 7 h post-treatment. The remaining eight sows per treatment were fitted with a transducer to allow determination of intrauterine pressure changes during 1 h pre-treatment until 5 h post-treatment. There were no differences among treatments for wean to estrus interval, size of ovarian follicles at the time of treatment or the estrus detection to ovulation interval. In all treatments, plasma PGFM concentrations were increased from 1 h after treatment. However, the increase was greater and of longer duration in the E-oil sows (P=0.03) supporting the suggestion that this formulation and route of administration enhanced uterine PGF2alpha release. Compared to controls, both estradiol treatments were associated with myometrial contractions of increased amplitude and duration, supporting a causal link between estradiol treatment, increased uterine PGF2alpha release, and enhanced myometrial contractility.     

Lysozyme, alkaline phosphatase and neutrophils in uterine secretions of mares with differing resistance to endometritis

A study was conducted to 1) determine differences in the inflammatory response following bacterial challenge between normal mares and mares with chronic endometritis and 2) to determine if enzyme activity in uterine fluid can be used to evaluate degree of inflammation in the equine uterus. Six normal mares (Group 1) and four mares with chronic endometritis (Group 2) received an intrauterine infusion of beta-hemolytic streptococci on the second day of estrus. Neutrophil concentration as well as lysozyme and alkaline phosphatase activity were determined in uterine secretions obtained by placing tampons in the uterus of mares. All mares had a similar inflammatory response following bacterial challenge of the uterus, as indicated by a neutrophil response of the same magnitude. Neutrophil numbers, lysozyme and alkaline phosphatase concentrations were all increased 12 h postinoculation and declined rapidly to normal preinoculation values by 48 h after inoculation. In spite of the similarity of the clinical signs, neutrophil concentrations and enzyme activity, mares in group 1 demonstrated a markedly higher ability to eliminate the infection than mares in group 2. It is concluded that factors other than neutrophil numbers, lysozyme and alkaline phosphatase activity account for the inability of the mare to eliminate uterine infections.     

Role of progesterone and estrogen in development of uterine tone in mares

In two experiments (30 mares/experiment), the uterus was recorded as having flaccid tone characteristic of estrus or seasonal anestrus (tone score 1), intermediate tone characteristic of diestrus (tone score 2), or increased or maximal tone characteristic of early pregnancy (tone score 3 or 4). In Experiment I (five mares/group), uterine tone in seasonally anovulatory mares was not altered significantly from the flaccid state by daily administration of 100 mg progesterone plus 1 mg estradiol 17beta or 1 mg estradiol 17beta alone. Uterine tone in seasonally anovulatory mares receiving 100 mg progesterone alone increased to intermediate level (score 2; P<0.05) and remained there throughout the treatment period. Tone scores in the group receiving a 14-d progesterone priming period followed by progesterone plus estradiol were higher (P<0.02) on Days 16 to 28 than scores in the group receiving progesterone alone throughout the treatment period. In Experiment II, (five mares/group), steroid treatments were begun on Day 10 postovulation. The combination of 1 mg exogenous estradiol plus progesterone produced greater uterine tone than exogenous progesterone alone. There were no significant differences between the pregnant control group and the group receiving progesterone plus 1 mg estradiol. There were no significant differences between the group receiving progesterone alone and the group receiving progesterone plus 5 mg estradiol. Results supported the hypothesis that the maximum uterine tone of early pregnancy is caused by progesterone priming followed by exposure to low levels of estradiol plus continued exposure to progesterone.     

The ovarian and uterine responses of Baixadeiro mares to prostaglandin synchronization during the dry and rainy seasons

This study aimed to evaluate the effect of synchronization with prostaglandin F2α in Baixadeiro mares during the rainy and dry seasons. Fourteen mares were synchronized by administering two doses of 1 mL prostaglandin PGF 2α and monitored by rectal palpation and ultrasound for the assessment of follicular development and uterine echotexture. Of this total, nine mares allowed the collection of blood, in which the blood was collected by venipuncture of the jugular vein to determine progesterone (P4) by ELISA. Mares showed no differences (P > 0.05) in weight, body score condition (BSC), tone, uterine edema, frequency of ovulation, synchronization interval, estrus, and the total number of follicles between periods. However, there was a difference in large increased follicle diameter (P < 0.05) during the dry season. The average concentrations of P4 in mares differed (P < 0.05) between the pre- and post-ovulatory phases for both seasons and after ovulation, with higher concentrations in the rainy season. Furthermore, statistical differences in daily light (P < 0.05) were observed between the dry and rainy periods. Thus, we conclude that mares from the genetic grouping Baixadeiro showed no reproductive seasonality, though there was a difference in luminosity between the rainy and dry seasons. The treatment with two doses of PGF 2α was effective in synchronizing the mares, promoting the return of estrus in the dry and rainy periods. The mares remaining cyclically active throughout the year provided there were appropriate forage availability and quality levels to allow for normal values of body weight and condition.     

Differential effects of progesterone treatment on the oxytocin-induced prostaglandin F2 alpha response and the levels of endometrial oxytocin receptors in ovariectomized ewes.

The oxytocin-induced uterine prostaglandin (PG) F2 alpha response and the levels of endometrial oxytocin receptors were measured in ovariectomized ewes after they had been given steroid pretreatment (SP) with progesterone and estrogen to induce estrus (day of expected estrus = Day 0) and had subsequently been treated with progesterone over Days 1-12 and/or PGF2 alpha over Days 10-12 postestrus. The uterine PGF2 alpha response was measured after an i.v. injection of 10 IU oxytocin on Days 13 and 14, using the PGF2 alpha metabolite, 13,14-dihydro-15-keto-PGF2 alpha (PGFM), as an indicator for PGF2 alpha release. The levels of oxytocin receptors in the endometrium were measured on Day 14. During the treatment with progesterone, the peripheral progesterone concentrations were elevated and remained above 1.8 ng/ml until the morning of Day 14. The PGFM responses to oxytocin in untreated controls and SP controls were low on both Days 13 and 14 whereas the levels of endometrial oxytocin receptors in the same ewes were high. Treatment with progesterone either alone or in combination with PGF2 alpha significantly (p less than 0.04) increased the PGFM response on Day 14 and reduced the levels of endometrial oxytocin receptors; treatment with PGF2 alpha alone had no effect. It is concluded that progesterone promotes the PGFM response to oxytocin while simultaneously suppressing the levels of endometrial oxytocin receptors. PGF2 alpha treatment had no effect on either the uterine secretory response to oxytocin or the levels of oxytocin receptors in the endometrium.(ABSTRACT TRUNCATED AT 250 WORDS)     

Biodegradable estradiol microspheres do not affect uterine involution or characteristics of postpartum estrus in mares

Quarterhorse mares were used to investigate effects of estradiol-17beta on uterine involution, duration of estrus, interval to ovulation, and fertility achieved by breeding on the first postpartum estrus. On the day of foaling, mares were injected with biodegradable poly (DL-lactide) microspheres containing either 100 mg estradiol-17beta (25 mares) or no drug (27 mares). The treatment period was considered to last for 12 to 15 d. Estrus was determined by teasing mares (n=16) with a stallion. Ovulation was detected by transrectal ultrasonographic examination of ovaries (n=48). On Days 6, 11 and 16 post partum, transrectal ultrasonography was used to measure cross-sectional diameters of the uterine body, uterine horns, and fluid within the uterine lumen (n=28). Uteri were swabbed for bacteriologic culture, and uterine biopsies were obtained from the previously gravid uterine horn on Days 11 and 16 post partum, for assessment of endometritis and morphometric analysis of endometrial histioarchitecture (n=19). Twenty-two mares were bred on foal-heat, and pregnancy was determined by transrectal ultrasonography on 14 to 16 and 30 to 35 d after breeding. With only one exception (diameter of previously gravid uterine horn on Day 11), mean values for all measures of uterine involution did not differ between treatment groups (P > 0.05). No differences were detected between treatment group means for length of estrus or interval to ovulation (P > 0.05). No differences were detected between treatment group liklihoods for recovery of potential bacterial pathogens, presence of endometritis, or presence of intrauterine fluid at 11 or 16 d post partum (P > 0.05). Pregnancy rate of mares treated with estradiol (5 11 ; 45%) was not different from that of control mares (9 11 ; 82%; P > 0.05). Estradiol treatment did not hasten uterine involution, increase duration of estrus, delay ovulation, or increase fertility in these postpartum mares.