Effect of ovariectomy on pregnancy in mares.

Pony mares were bilaterally ovariectomized at different stages of pregnancy between Days 25 and 210. Abortion or fetal resorption occurred within 2 to 6 days after operations in all 14 mares ovariectomized between Days 25 and 45 and after an interval of 10 to 15 days in 9 of 20 other ovariectomized between 50 and 70 days. All 12 mares ovariectomized on either 140 or 210 days carried their foals to normal term. The termination of early pregnancy was preceded by a loss of uterine tone and of a palpable uterine bulge. The mean length of gestation in all mares in which pregnancy was not interrupted by ovariectomy was not significantly different from that in a group of contemporary control mares. Plasma progestagen concentrations dropped to less than 2 ng/ml after ovariectomy, whether or not pregnancy was maintained. Mares ovariectomized on Day 25 and injected with 100 mg progesterone daily for 10 or 20 days remained pregnant during treatment but showed a loss of uterine tone and the fetal bulge disappeared within 4 to 6 days after the end of treatment. Non-pregnant ovariectomized or intact seasonally anoestrous mares injected i.m. with 50 or 100 mg progesterone daily for 8 weeks showed changes in uterine tone, length and thickness similar to those occurring in mares during early pregnancy.     

The use of radioreceptor assay for the detection of pregnancy in the mare

Jugular blood samples were collected between 42-45 days from the last breeding for measurement of pregnant mare serum gonadotropin (PMSG) and progesterone in 46 pregnant mares. A radioreceptor assay (RRA) was developed to measure human chorionic gonadotropin (hCG) and subsequently modified to measure PMSG. Highly purified hCG was iodinated using a lactoperoxidase enzymatic procedure and served as the labeled antigen for both the hCG and PMSG RRA. Standard curves were generated using purified hCG or PMSG. Bovine corpora lutea served as the receptor source. The assay was conducted at 37 degrees C for one hour with a total elapsed time from preparation of the luteal cell homogenate until final results were calculated of 2.5 hours. Twelve of the 46 mares failed to maintain their pregnancy, returned to estrus and reovulated after 45 days post-breeding (non-foaling mares). Thirty-four of the 46 mares delivered foals following a gestation of normal length. Mean concentrations of PMSG in the foaling mares was higher than in non-foaling mares. A concentration of 6.9 I.U. of PMSG/ml was used as the lowest concentration necessary for the confirmation of pregnancy. Five of the mares delivering foals had low concentrations of PMSG and were called non-pregnant. Thus, the incidence of false negatives by RRA was 14.7%. All of the non-foaling mares were correctly diagnosed non-pregnant for an error rate (false positive) of 0.0. Mare Immunological Pregnancy (MIP) tests on the 12 non-foaling mares indicated three false positives - an error rate of 25%. Of the 34 foaling mares, the MIP test indicated 8 inconclusive or false negatives, an error rate of 23.5%. At day 42-45, there was no significant difference in progesterone concentrations (determined by RIA) between foaling and non-foaling mares. RRA is a quick, accurate and quantitative method for measuring PMSG in the mare and can be used to diagnose pregnancy at 42-45 days post-ovulation. Plasma progesterone concentrations at this time were not associated with subsequent pregnancy maintenance as were plasma PMSG concentrations.     

The effect of treatment with flunixin meglumine at different times relative to hCG administration on ovulation failure and luteal function in mares

Flunixin meglumine (FM), a prostaglandin synthetase inhibitor, causes ovulatory failure in the mare. However, the effect of the FM treatment relative to the time of hCG administration on the ovulation failure has not been determined nor has its effect on the luteal function of treated mares. Estrous mares with a follicle ≥32 mm (range of 32-38 mm) were treated with 1.7 mg/kg b.w. of FM iv at zero, 12, 24 and 36 h (n=6), at 24 and 36 h (n=6), at 28 and 36 h (n=6), at 24h (n=6) or at 30 h (n=6) after treatment with 1500 IU hCG. One group received no FM (control, n=6). Progesterone concentrations were determined using RIA. Mares treated with FM 0-36 h and 24-36 h had higher (P<0.05) incidence of ovulatory failure (83 and 80%, respectively) than mares treated twice at 28 and 36 h, or once at 24 or at 30 h after hCG (16.7, 0 and 0%, respectively). The anovulatory follicles of FM treated mares luteinized and produced progesterone (>2 ng/ml). The progesterone concentration was lower in mares treated with FM at zero to 36 h and at 24-36 h after hCG than in the other groups. In conclusion, the FM administration was effective in blocking ovulation only when the treatment began ≤24 h after hCG and was continued every 12 h until ≥36 h. In addition, the FM-induced anovulatory follicles underwent luteinization of follicular cells with active production of progesterone.     

Cell proliferation patterns during development of the equine placenta

Placentation involves considerable growth and reorganization of both maternal and fetal tissues. In this investigation, immunohistochemical localization of the proliferation marker Ki-67 antigen was used to monitor cell division during placentation in mares. Endometrial biopsies were obtained from eight mares between day 14 and day 26 of pregnancy and from eight anoestrous mares that had been treated with various combinations of progesterone and oestrogen. Samples of endometrium and fetal membranes were obtained from 19 mares carrying normal horse conceptuses between day 30 and day 250 of gestation and from three failing extraspecific donkey-in-horse pregnancies. Proliferation in the superficial strata of the endometrium was increased by day 18 of gestation and this effect could be mimicked by supplementing with oestradiol benzoate during the last 6 days of a prolonged period (18-36 days) of progesterone administration. Fetal chorionic girdle cells were proliferating vigorously at days 30-32 of gestation, but stopped dividing after they invaded the endometrium, while the trophoblast cells of the allantochorion showed an increase in mitotic activity after day 38. The luminal epithelium of the endometrium started to proliferate only after the primary villi of the true epitheliochorial placenta had been formed, and during days 58-70 this effect was seen only in the pregnant horn in which placentation was further advanced. During the second half of gestation, most of the mitotic activity was confined to the periphery of the microcotyledons which were still growing. In the donkey-in-horse pregnancies, proliferation rates of the maternal and fetal epithelial at day 70 of gestation were markedly reduced in areas of heavy endometrial lymphocyte infiltration and poor placentation. These results provide a basis for further studies on factors that influence invasive and non-invasive placentation.     

Concentrations of nitric oxide in equine preovulatory follicles before and after administration of human chorionic gonadotropin

In the present study, follicular fluids of estrous mares treated with saline solution (Control) or nitric oxide synthase (NOS) inhibitors were analyzed for nitric oxide (NO), estradiol-17beta (E2) and progesterone (P4) concentrations before and 36h after administration of human chorionic gonadotropin (hCG). Follicular fluids obtained before (0h) hCG administration from control mares had lower concentrations of NO than those obtained 36h after administration of hCG (58.3+/-17.8 micromol versus 340.4+/-57.7 micromol; P<0.05). A similar pattern was also noted for intrafollicular P4 in control mares, which had lower concentrations of intrafollicular P4 before hCG than 36h post-hCG administration (P<0.05). As expected, E2 concentrations of control follicles sampled before hCG administration were higher than those sampled 36h post-hCG administration (P<0.05). However, the E2 concentrations in follicles of mares treated with the NOS inhibitors N(omega)-nitro-L-arginine methyl ester (L-NAME) or aminoguanidine (AG) did not decrease after hCG administration, unlike those in control mares (P>0.10). In addition, mares treated with NOS inhibitors had lower intrafollicular concentrations of NO and P4 than control mares, both before and after hCG administration (P<0.05). Increased intrafollicular concentrations of NO in control, hCG-stimulated mares provide evidence for the presence of an NO-generating system in the equine preovulatory follicle that is likely upregulated following administration of hCG.     

Effect of periovulatory prostaglandin F2alpha on pregnancy rates and luteal function in the mare.

The objective of this study was to determine whether periovulatory treatments with PGF2alpha affects the development of the CL, and whether the treatment was detrimental to the establishment of pregnancy. Reproductively sound mares were assigned randomly to one of the following treatment groups during consecutive estrus cycles: 1. 3,000 IU hCG within 24 hours before artificial insemination and 500 microg cloprostenol (PGF2alpha analogue) on Days 0, 1, and 2 after ovulation (n=8), 2. 2 mL sterile water injection within 24 hours before artificial insemination and 500 microg cloprostenol on Days 0, 1, and 2 after ovulation (n=8); 3. 3,000 IU hCG within 24 hours before artificial insemination and 500 microg cloprostenol on Day 2 after ovulation (n=8); or 4. 3,000 IU hCG within 24 hours before artificial insemination and 2 mL of sterile water on Days 0, 1, and 2 after ovulation (controls; n=8). Blood samples were collected from the jugular vein on Days 0, 1, 2, 5, 8, 11, and 14 after ovulation. Plasma progesterone concentrations were determined by the use of a solid phase 125I radioimmunoassay. All mares were examined for pregnancy by the use of transrectal ultrasonography at 14 days after ovulation. Mares in Group 1 and 2 had lower plasma progesterone concentrations at Day 2 and 5, compared to mares in the control group (P < 0.001). No difference was detected between group 1 and 2. Plasma progesterone concentrations in group 3 were similar to the control group until the day of treatment, but decreased after treatment and were significantly lower than the control group at Day 5 (P < 0.001). Plasma progesterone concentrations increased in all treatment groups after Day 5, and were comparable among all groups at Day 14 after ovulation. Cloprostenol treatment had a significant effect on pregnancy rates (P < 0.01). The pregnancy rate was 12.5% in Group 1, 25% in Group 2, 38% in Group 3, and 62.5% in Group 4. It was concluded that periovulatory treatment with PGF2alpha has a detrimental effect on early luteal function and pregnancy.     

Effect of diethylstilboestrol on the relationship between LH, PMSG and progesterone during pregnancy in the mare.

Two studies were conducted to determine the relationship between LH and progesterone and between PMSG and progesterone during pregnancy in mares. In the first, samples of jugular blood were collected daily from 7 mares from the first day of oestrus until Day 28 of pregnancy, and in the second, samples were collected weekly from 14 mares from Day 35 of gestation until parturition. In an attempt to prolong secretion of progesterone from accessory corpora lutea, 7 of these 14 mares were injected with increasing doses (2--10 mg) of diethylstilboestrol (DES) between Days 84 and 142 of gestation. The remaining 7 mares received injections of vehicle. Concentrations of LH, PMSG and progesterone in serum were determined by radioimmunoassay. From the onset of oestrus until Day 4 of gestation, serum concentrations of LH and progesterone were negatively correlated (r = 0.67, P less than 0.01), but from Days 5 to 28 a positive correlation (r = 0.80, P less than 0.01) was noted. Likewise, serum concentrations of PMSG and progesterone were highly correlated between Days 35 and 196 in mares injected with DES (r = 0.72, P less than 0.01) and the vehicle (r = 0.75, P less than 0.01). Injections of DES did not influence serum concentrations of LH, PMSG or progesterone, or affect the length of gestation. It was concluded that DES does not influence the maintenance of pregnancy in the mare.     

In-vitro and in-vivo responsiveness of the corpus luteum of the mare to gonadotrophin stimulation

Dispersed horse luteal cells were used to evaluate the ability of horse LH, hCG and PMSG to stimulate progesterone secretion in vitro. Morphological characterization of these cells before gonadotrophin stimulation indicated the presence of two populations of cells based on cell diameters. In luteal cells incubated as suspended cells, horse LH and hCG stimulated (P less than or equal to 0.05) progesterone production at all levels of treatment. Stimulation of progesterone secretion by hCG was greater (P less than or equal to 0.05) than by horse LH over the range of concentrations utilized. When mares (N = 7) received an intramuscular injection of 1000 i.u. hCG on Days 3, 4 and 5 after the end of oestrus, there was an increase (P less than or equal to 0.05), in peripheral progesterone concentrations beginning on Day 7 and continuing until Day 14 compared with controls (N = 7). Peripheral progesterone concentrations continued to be elevated in hCG-treated mares for Days 15-30 after oestrus in those mares that conceived. Although treatment with hCG increased progesterone concentrations, it had no influence on anterior pituitary release of LH as measured by frequency and amplitude of LH discharge. We conclude that the mare corpus luteum is responsive to gonadotrophins in vitro and that exogenous hCG can enhance serum progesterone concentrations throughout the oestrous cycle and early pregnancy.     

Ontogeny of uteroplacental progestagen production in pregnant mares during the second half of gestation

In pregnant mares during late gestation, little, if any, progesterone (P4) is found in the maternal circulation. Hence, quiescence of the equine uterus is believed to be maintained by metabolites of pregnenolone and P4 known as progestagens, which are produced by the uteroplacental tissues. However, little is known about the ontogeny, distribution, or actual rates of uteroplacental progestagen production in pregnant mares and their fetuses during the second half of pregnancy. Therefore, the present study measured the rates of uteroplacental uptake and output of eight specific progestagens in chronically catheterized, pregnant pony mares from 180 days to term. No significant uteroplacental uptake of any of the eight individual progestagens was observed from the uterine circulation. In contrast, significant uteroplacental uptake was observed for five of the eight individual progestagens from the umbilical circulation, and the uptakes increased toward term. The major uteroplacental progestagen outputs were 5 alpha-pregnane-3,20-dione (5 alphaDHP) and 20 alpha-hydroxy-5 alpha-pregnan-3-one (20 alpha 5P). These were released into both the umbilical and uterine circulations at rates that increased toward term. The majority of the total uteroplacental 20 alpha 5P output was distributed into the uterine circulation at all gestational ages studied. In contrast, distribution of the total uteroplacental 5 alphaDHP output switched from preferential delivery into the uterine circulation before 220 days of gestation to release predominantly into the umbilical circulation after 260 days. These findings demonstrate that uteroplacental progestagen production changes during the second half of gestation, which may have important implications for the maintenance of pregnancy and the onset of labor in the mare.     

Effects of bromocriptine and perphenazine on prolactin and progesterone concentrations in pregnant pony mares during late gestation

Pregnant pony mares in Group A (n = 4) received i.m. injections at 07:00 and 17:00 h of 0.8 mg bromocriptine/kg body weight 0.75 per day beginning on Day 295 of gestation and continuing until parturition. Group B (n = 4) was treated similarly, but perphenazine was administered orally at 0.375 mg/kg body weight twice a day beginning on Day 305 of gestation and continuing until parturition. Mares in Group C (n = 3) received i.m. injections of saline. Mean plasma prolactin and progesterone concentrations were greater (P less than 0.05) for mares in Group C than in Groups A and B from 295 to 309 days of gestation. From 305 days of gestation, plasma prolactin and progesterone concentrations were greater (P less than 0.05) in Group B and C than in Group A mares. Progesterone and prolactin concentrations increased over this period for Group B and Group C mares, but remained constant in Group A mares. From 10 days pre partum through foaling, mares in Group A had lower progesterone (P less than 0.05) and prolactin (P less than 0.01) concentrations than Group B and C mares. All mares in Group A were agalactic at foaling, while all mares in Groups B and C had normal milk secretion. Gestation was longer (P less than 0.05) in Group A than in Group C mares. In Group A, 2 mares retained the placenta for greater than 3 h, 3 mares had dystocia and all 4 mares had thickened, haemorrhagic placentae.(ABSTRACT TRUNCATED AT 250 WORDS)     

Serum and urinary hormones during pregnancy and the peri- and postpartum period in an Asian elephant (Elephas,maximus)

Blood and urine samples were collected weekly from an Asian elephant (Elephas maximus) for 10 months before conception, throughout pregnancy, and for 10 months after parturition. Additional daily samples were collected for 41 days before through 10 days after parturition to define endocrine events during the peripartum period. During gestation, serum progesterone concentrations increased gradually and, after ～13 weeks, were higher (P < 0.05) than those observed during the nonpregnant luteal phase. Concentrations peaked at ～12 months of gestation, gradually declined during the last month, and then decreased sharply to nondetectable levels 2 days before parturition. A 12 week lactational anestrus was observed before cyclicity resumed. The urinary profile of progestagen excretion paralleled that of circulating progesterone (r = 0.79; P < 0.05); however, radioimmunoassay of HPLC-separated fractions of urinary eluates indicated that this immunoactivity was not associated with native progesterone. After remaining basal through the first 16 weeks of gestation, serum prolactin concentrations increased to 100-fold about midterm and remained elevated until after parturition. Neither serum nor urinary cortisol concentrations were altered during pregnancy, but both increased markedly the day after parturition and remained elevated above prepartum levels for several weeks thereafter. These data indicate that analysis of serum prolactin can confirm pregnancy in the Asian elephant after ～4 months of gestation and that daily monitoring of serum or urinary progestagens is useful for predicting parturition. © 1995 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Luteolytic action of 15-keto prostaglandin F2alpha in the rhesus monkey.

The naturally-occurring metabolite of prostaglandin F2alpha, 15-keto prostaglandin F2alpha (15-keto PGF2alpha), elicited rapid and sustained declines in serum progesterone concentrations when administered to rhesus monkeys beginning on day 22 of normal menstrual cycles. Evidence for luteolysis of a more convincing nature was obtained in studies where a single dose of 15-keto PGF2alpha was given on day 20 of ovulatory menstrual cycles in which intramuscular injections of hCG were also given on days 18-20; serum progesterone concentrations fell precipitously in monkeys within 24 hours following intramuscular administration of 15-keto PGF2alpha. However, corpus luteum function was impaired in only 4 of 11 early pregnant monkeys when 15-keto PGF2alpha was administered on days 30 and 31 from the last menses, a time when the ovary is essential for the maintenance of pregnancy. Gestation failed in 2 additional monkeys 32 and 60 days after treatment with 15-keto PGF2alpha, but progressed in an apparently normal manner in the remaining 5 animals. Two pregnant monkeys treated with 15-keto PGF2alpha on day 42 from the last menstrual period, a time when the ovary is no longer required for gestation, continued their pregnancies uneventfully. Corpus luteum function was not impaired in 9 control monkeys which received injections of vehicle or hCG at appropriate times during the menstrual cycle or pregnancy.     

The effect of exogenous progestins on endogenous progesterone secretion in pregnant mares

Twenty-four pregnant, light horse mares were used in a study to determine if an exogenous progestin or progesterone would alter serum concentrations of progesterone. On day 40 of gestation, mares were randomly assigned to one of three administration groups: 1) 250 mg of progesterone in oil every other day, 2) 22 mg of Altrenogest (Regumate, American Hoechst, Somerville, NJ 08876) orally every day, or 3) 10 ml of neobee oil (control) orally every day. The treatment period was from day 40 to 105. Pregnancy status was monitored on days 40, 60, 80, 100 and 105 and a single jugular blood sample was obtained daily from days 40 to 46, 69 to 75 and 99 to 105. Serum concentrations of progesterone were determined by radioimmunoassay. Concentrations of progesterone were similar (P>0.05) among groups at each sampling period. Overall concentrations of progesterone increased (P<0.001) from days 40 to 46. Injection of 250 mg of progesterone in oil failed (P>0.05) to maintain concentrations of progesterone in serum above baseline for 24 hr. Thus higher doses and/or more frequent injections would be needed in order to increase concentrations of progesterone above those seen in untreated controls. In summary, Altrenogest was found to be a nonstressful, convenient method of administering progestins to pregnant mares without altering their endogenous secretion of progesterone.     

Factors controlling epidermal growth factor (EGF) gene expression in the endometrium of the mare

Previous studies showed a dramatic increase in EGF gene expression in the endometrial glands of pregnant mares around day 40 after ovulation. To investigate how the steroid hormones of pregnancy might regulate this expression, in situ hybridization was used to monitor the levels of EGF mRNA in endometrial biopsies obtained from seasonally anoestrous or ovariectomised mares given exogenous progesterone and oestrogen, alone or in combination, for up to 46 days. Biopsies were also taken from mares during the non‐pregnant cycle, during normal pregnancies and pregnancies compromised by endometrial pathology (endometrosis) or because of incompatible extraspecific embryo transfers (donkey‐in‐horse pregnancies). Only a few samples showed weak EGF expression during the late luteal phase of the oestrous cycle. During normal pregnancy, the previously observed dramatic increase of expression after day 40 of gestation was confirmed. Although aged mares suffering from endometrosis and mares carrying an extraspecific donkey conceptus showed the same increase of EGF mRNA in normal glands, this was virtually absent from gland cross‐sections compromised due to inflammatory or fibrotic changes. Administration of various doses and combinations of progesterone and oestrogen for <35 days yielded negative or only weakly positive hybridization results, whereas progesterone alone for ≥40 days upregulated EGF expression strongly irrespective of additional treatment with oestrogen. This is the first experimental evidence that EGF expression in the endometrium can be induced by progesterone alone. The requirement for prolonged progesterone priming is of considerable interest in the context of the unusually late stage of gestation at which placental attachment commences in equids. Mol. Reprod. Dev. 53:255–265, 1999. © 1999 Wiley‐Liss, Inc.     

Oxytocin does not contribute to the effects of cervical dilation on progesterone secretion and embryonic development in mares

The aim of the present study was, to investigate the effects of oxytocin administration on Day 7 post-ovulation on progesterone secretion, pregnancy rate and embryonic growth in mares. Endogenous stimulation of oxytocin release was compared to the administration of native oxytocin or the long-acting oxytocin analogue carbetocin. At Day 7 after ovulation, mares had to undergo four treatments in a crossover design: (a) control, (b) oxytocin (10 IU i.v.), (c) carbetocin (280 microg i.m.) and (d) cervical dilation. On Day 13, all mares (8 of 8 mares) were pregnant on groups control, oxytocin and carbetocin and only 6 of 8 mares on group dilation. In one mare uterine fluid accumulation and uterine edema from Day 6 to 13 and early embryonic death by Day 11 occurred during dilation treatment. Another mare, which did not become pregnant during dilation treatment, developed uterine fluid accumulation and uterine edema from Day 10 to 14. Mean growth rates of the conceptuses did not differ among treatment groups and individual growth rates varied in a wide range from -0.1 to 0.8 cm per day. At Day 13, mean diameters of conceptuses yielded 1.4+/-0.1 cm in control group, 1.5+/-0.1 in oxytocin and carbetocin group and 1.3+/-0.2 cm in dilation group. Secretion of progesterone was not affected by treatments. Administration of oxytocin and carbetocin caused similar maximum plasma concentrations of oxytocin, but onset and duration of peaks differed. Maximum concentrations after intramuscular application of carbetocin were obtained almost 20 min later when compared to intravenous administration of oxytocin. Duration of peaks after injection of the long-acting oxytocin analogue was more than three-fold longer than after administration of native oxytocin. In conclusion, the present study showed that single administration of oxytocin or its long-acting analogue carbetocin at Day 7 after ovulation did not affect progesterone secretion, pregnancy rate and embryonic growth. Two possible scenarios concerning the effects of cervical dilation were observed: In the majority of mares, dilation of the caudal half to two-third of the cervical lumen up to a diameter of 4.5 cm had no negative consequences on progesterone secretion and pregnancy outcome. However, cervical dilation caused uterine inflammation and subsequent luteolysis in two mares and early embryonic death in one of them. Thus, manipulation of the cervix itself seems not to have negative impact on success rates of transcervical transfer of embryos in the mare.     

Early effects of equine FSH (eFSH) treatment on hormonal and reproductive parameters in mares intended to carry their own pregnancy

Superovulatory treatment may potentially increase the embryo recovery rate and the per-cycle pregnancy rate in normal or subfertile mares that are managed properly. However, some studies suggest a possible negative effect of superovulatory treatment on ovarian follicular maturation and embryo viability. Objectives of the present study were to investigate the early effects of eFSH treatment in reproductively normal mares in terms of: folliculogenesis, pregnancy rate, early embryonic development, reproductive tract parameters (tone and edema), and serum estradiol-17β and progesterone concentrations. Reproductively sound mares (n = 26) were evaluated daily by transrectal palpation and ultrasonography. Five days after spontaneous ovulation, mares were randomly assigned to one of two treatment groups. In the eFSH group, mares (n = 16 estrous cycles) were administered eFSH twice daily; beginning when a follicle ≥20 mm was detected, and continuing until at least one follicle reached a diameter of ≥35 mm. PGF2α was administered 2 days following initiation of eFSH therapy, and hCG was administered approximately 36 h after cessation of eFSH therapy. In the control group, mares (n = 26 estrous cycles) were administered PGF2α 7 days after spontaneous ovulation, and hCG when a follicle ≥35 mm was detected. All mares were bred with fresh semen, monitored for ovulation (Day 0), and evaluated for pregnancy on Days 11–16. Serum estradiol-17β and progesterone concentrations were analyzed using radioimmunoassay on the Day of hCG administration, and Days 8, 11 and 16. Mares treated with eFSH had more follicles ≥30 mm at the time of hCG administration (2.6 ± 0.4 compared with 1.1 ± 0.1; P < 0.01), and more ovulations (2.3 ± 0.5 compared with 1.1 ± 0.3; P < 0.01). However, pregnancy rates were not significantly different between groups (50%; 8/16 compared with 62%; 16/26). Mean overall daily growth rate of embryonic vesicles from Day 11 to 16 was not statistically different between the two groups (3.3 ± 0.3 compared with 3.7 ± 0.1 mm/day) (P = 0.2); however, was more variable (P < 0.01) in the eFSH group (95%CI: 2.6–3.8 mm/day) than in the control group (95%CI: 3.5–3.9 mm/day). Administration of eFSH modified the reproductive tract variables and serum concentrations of progesterone and estradiol-17β on the days that oocyte maturation, fertilization, and early embryonic development are expected to occur. These alterations may be related to the greater incidence of non-ovulatory follicles (25% compared with 0%), fewer embryos per ovulation rate (0.3 ± 0.1 compared with 0.6 ± 0.1), and the lesser than expected pregnancy rates in the eFSH-treated mares.     

Follicle and systemic hormone interrelationships during induction of luteinized unruptured follicles with a prostaglandin inhibitor in mares

The objective was to determine differences in follicle and reproductive hormone characteristics in mares with ovulatory and flunixin meglumine (FM)-induced anovulatory cycles. Estrous mares were given 1500 IU hCG when the follicle was ≥ 32 mm (0 h). In Experiment 1, control mares (n = 7) were not treated further. The remaining mares (n = 11) were given 1.7 mg/kg FM i.v. twice daily, from 0 to 36 h after hCG treatment. Blood samples and ultrasonographic examinations were performed every 12 h. All control mares ovulated normally between 36 and 48 h. In contrast, eight of 11 FM mares did not ovulate, but developed luteinized unruptured follicles (LUFs). Three FM-treated mares did not develop conventional LUFs. Plasma progesterone concentrations were lower (P < 0.05) in LUF mares at 96, 120, and 216 h than in controls, whereas plasma LH concentrations were higher (P < 0.05) between 108 and 120 h in LUF mares than in controls. Plasma concentrations of PGFM and estradiol did not differ significantly between groups. In Experiment 2, the three mares that did not develop LUFs were treated, during the consecutive cycle, with the same dose of FM but with increased frequency at zero, 12, 24, 30, 36, and 48 h after hCG. One mare formed a LUF, whereas the other two did not. These two mares had lower LH concentrations than LUF or control mares in the two consecutive cycles. In conclusion, systemic treatment with FM blocked ovulation in 73% of treated mares. Mares with LUFs had lower progesterone and higher LH concentrations than control mares.     

Plasma progestogen levels in pregnant mares following administration of exogenous progesterone

Twelve pregnant mares were used in a switchback design with two groups of six mares each. On day 255 of gestation, group A was administered repository progesterone (250 mg, IM) and group B progesterone in sesame oil (250 mg, IM). Jugular vein plasma was taken 15 min pre-injection and post-injection at 30 min, 1, 3, 6, 9, 12, and 24 hours. Additional samples were taken on days 2, 3, 4, 6, and 8. Both groups were then assigned to the opposite treatment on day 270 of gestation. Concentrations of plasma progestogens after injection with progesterone in sesame oil were not different (P>.05) from values obtained using repository progesterone through the 8 days studied. Mean progestogen concentrations after injection of progesterone in sesame oil were, however, consistently higher through 48 hr than those given repository progesterone. Concentrations of progestogens were not different (P>.05) from pre-injection concentrations by day 6 post-injection using either vehicle.     

Reproductive management of mares without detection of oestrus.

The use of photoperiod, progestagen, prostaglandin and hCG treatments was investigated to obtain mating of mares at predetermined times. The objectives were: (1) synchronization of oestrus at an early time of the year, (2) simplification of treatment schedules by use of vaginal sponges, and (3) use of several controlled cycles by successive synchronization. The following conclusions were reached. First, after a 16 h photoperiod was applied beginning on 25 November, hormonal synchronization of oestrus and ovulation followed by cyclicity were obtained on 1 February; i.e. 2 months of light are essential as hormonal synchronization of ovulation was not obtained by 10 January. Second onset of oestrus was well synchronized after vaginal application of progestagens (3.75 days +/- 0.98 s.d. after withdrawal) and in spite of vaginal irritation, fertility was high (71%, N = 24) after mating every 48 h of the induced oestrus. Third, for synchronization of return to oestrus in mated non-conceiving mares, oral progestagens were given from Days 7 to 21 after mating. Predetermined mating (Days 27 and 29) and hCG injection (day 28) for non-pregnant animals were decided after a progesterone assay of Day 21 blood plasma. After 3 controlled mating periods, the cumulative fertility was 88% (N = 24) in non-lactating mares and 58% (N = 19) in lactating mares. Programmed reproductive management is possible in the horse.     

Effects of age and altrenogest treatment on conceptus development and secretion of LH, progesterone and eCG in early-pregnant mares

The treatment of early pregnant mares with a history of repeated early embryonic loss with the progestin altrenogest has become routine; however no controlled studies on the efficiency of altrenogest to prevent embryonic losses are available so far. In the present study, we have investigated effects of altrenogest treatment in mares on conceptus development and the secretion of LH, progesterone, and eCG until day 100 of pregnancy. In addition, differences related to age of mares were assessed. Mares were treated with altrenogest (0.044 mg/kg per os once daily) or sunflower oil (10 ml per os once daily) from day 6 to day 100 after ovulation. Blood samples for analysis of LH, progesterone, and eCG were collected. The size of the embryonic vesicle and embryo/fetus was determined by ultrasound. No difference in the per cycle pregnancy rate between altrenogest-treated (75%) and sunflower oil-treated mares (74%) was detected (n.s.). A significant effect of age but not of altrenogest treatment on mean diameter of the embryonic vesicle was found between days 12 and 22 of pregnancy (e.g. day 15: control, 4-8 years: 22.9 ± 1.0 mm, >8 years: 22.0 ± 1.7 mm, altrenogest, 4-8 years: 26.1 ± 2.0 mm, >8 years: 20.4 ± 1.0 mm, P < 0.05). A significant effect of age and treatment on size of the embryo proper between days 30 and 45 was detected (P < 0.05). In the control group but not in the altrenogest group, size of the embryo proper respective fetus was negatively correlated with age of the mares (day 30: r = −0.834, P < 0.05; day 35: r = −0.506, P < 0.05). Plasma concentrations of LH and progesterone were neither effected by age nor by treatment of mares, but significant effects of age and altrenogest treatment on eCG concentrations between days 40 and 130 were detected (P < 0.05). The present study demonstrates for the first time a positive influence of altrenogest-treatment on a retarded development of the embryo respective fetus around the beginning of placentation in mares older than 8 years.