Pony Mares Research Articles

The effect of intra-uterine devices on the reproductive physiology and behaviour of pony mares

Spherical (35 mm diameter) glass intra-uterine devices (IUDs) are commonly understood to modify sexual behaviour in performance mares. The effect of IUDs on the endocrinology (luteinising hormone, oestradiol, progesterone, testosterone), ovarian and uterine function, sexual and social behaviours associated with the ovarian cycle were evaluated during the natural breeding season in nine, nuliparous pony mares (4.6±0.5 years old, 230±12 kg bodyweight). Age and weight-matched groups were allocated to sham-treatment (n=5) or IUD-implantation (n=4) groups. Fifty complete ovarian cycles were evaluated, with 26 ovarian cycles monitored for the nine mares prior to treatment and a further 12 cycles were evaluated for mares in each of the groups post-treatment. Detailed characterisation of cyclic reproductive changes in the pony may be of value for controlled breeding programmes. The presence of an IUD was well-tolerated, but failed to modify any recorded aspect of reproductive physiology or behaviour.

Prostaglandin H synthase Type 2 is differentially expressed in endometrium based on pregnancy status in pony mares and responds to oxytocin and conceptus secretions in explant culture

The equine embryo must signal its presence to the uterus for pregnancy to continue to term. Mobility of the conceptus throughout the uterus is crucial for its survival, and this action presumably permits the conceptus to transmit its antiluteolytic signal to the endometrium. Studies were completed to establish whether this unidentified antiluteolytic signal targets prostaglandin G/H synthase 2 (PGHS2), a rate limiting enzyme in converting arachidonic acid to prostaglandins (PGs). In the first study, quantitative RT-PCR was used to determine the relative abundance of PGHS2 mRNA in endometrium derived from estrous cyclic and pregnant mares on day 14 post-ovulation. PGHS2 mRNA abundance was substantially greater in endometrium from estrous cyclic mares. Additional studies were completed to better understand PGHS2 in equine endometrium. An estrogen and progesterone treatment regimen in ovariectomized mares was developed as a test model for detecting endometrial PGHS2 mRNA. Also, exposing endometrial explants to conceptus secretions (conditioned culture medium) decreased PGHS2 mRNA abundance whereas exposing explants to oxytocin increased PGHS2 mRNA abundance. Exposure to conceptus secretions also decreased PGF2α concentrations in explant-conditioned medium whereas oxytocin supplementation increased PGF2α concentrations in medium. These data support the hypothesis that PGHS2 is a target for the antiluteolytic signal produced by equine conceptuses during early pregnancy. Also, the endometrial explant culture system used for these studies can serve as a model for identifying and characterizing the maternal recognition of pregnancy factor in equids.

Vascular perfusion of reproductive organs in pony mares and heifers during sedation with detomidine or xylazine

To assess the vascular effects of detomidine and xylazine in pony mares and heifers, respectively, as determined in a major artery and by extent of vascular perfusion of reproductive organs. 10 pony mares and 10 Holstein heifers. Pony mares were assigned to receive physiologic saline (0.9% NaCl) solution (n = 5) or detomidine (3.0 mg/mare, IV; 5). Heifers were assigned to receive saline solution (5) or xylazine (14 mg/heifer, IM; 5). Color Doppler ultrasonographic examinations were performed immediately before and 10 minutes after administration of saline solution or sedative. In spectral Doppler mode, a spectral graph of blood flow velocities during a cardiac cycle was obtained at the internal iliac artery and at the ovarian pedicle. In color-flow mode, color signals of blood flow in vessels of the corpus luteum and endometrium were assessed. Systemic effects of sedation in the 2 species were evident as a decrease in heart rate; increase in duration of systole, diastole, or both; decrease in volume of blood flow; and decrease in velocity of blood flow within the internal iliac artery. However, an effect of sedatives on local vascular perfusion in the ovaries and endometrium was not detected. Sedation with detomidine in pony mares and xylazine in heifers did not affect vascular perfusion in reproductive organs. These sedatives can be used in experimental and clinical color Doppler evaluations of vascular perfusion of the corpus luteum and endometrium.

Uterine involution and endometrial function in postpartum pony mares

To determine endometrial regeneration in postpartum mares by analysis of histologic features, apoptosis and cell proliferation markers, lectin binding, cytokines, and progesterone and estrogen receptors in endometrial biopsy specimens. 9 postpartum mares. Mares were examined on postpartum days 1, 9, and 16, and uterine biopsy specimens were obtained for histologic examination. Lectin binding was analyzed histochemically, and expressions of Ki-67 antigen (proliferation marker), lysozyme, and caspase 3 (apoptosis marker) were studied immunohistochemically. Gene expressions for cytokines (interleukin-1beta, -6 and -8 and tumor necrosis factor-alpha), cyclooxygenase 2, prostaglandin-E-synthase, and estrogen and progesterone receptors were determined by use of quantitative real-time PCR assay. On day 1, neutrophils predominated but by day 9 had largely been replaced by lymphocytes and macrophages. High numbers of cells with staining for caspase 3 were found on day 1, but numbers decreased by day 9. In contrast, the number of cells with staining for Kiel 67 antigen increased between days 1 and 9. Lectin binding to the endometrium changed over time. Relative mRNA expressions for cytokines and prostaglandin-E-synthase did not differ among days. Expressions of progesterone and estrogen receptors were minimal on day 1 and increased by day 9. Early postpartum endometrial cells underwent apoptosis, but during the second week, postpartum proliferation of cells predominated. Lectin binding reflected changes in endometrial glycocalyx patterns. Increased expression of estrogen receptors allowed the endometrium to respond to estrogen during foal heat, and in subsequent diestrus, the endometrium was able to respond to progesterone.

Kisspeptin immunoreactive neurons in the equine hypothalamus: Interactions with GnRH neuronal system

To determine if kisspeptin could be implicated in the control of reproduction in equine species, we studied the distribution of kisspeptin neurons and their anatomical interactions with GnRH neurons in the hypothalamus of pony mares. Brains were collected in three pony mares between 2 and 4 h after ovulation. One major population of kisspeptin immunoreactive cell bodies was found in the arcuate nucleus (ARC), where they extended from the middle of the nucleus to the premammillary recess. Kisspeptin immunoreactive varicose fibers extended from the preoptic area to the mammillary nuclei, with important densities especially in the anterior periventricular area and the median eminence (ME). Rare close appositions of kisspeptin fibres on GnRH cell bodies were observed in the ARC. Close appositions between kisspeptin and GnRH fibres were also confirmed at a low incidence in the anterior basal periventricular area and at a high incidence in the ME. This work provides neuroanatomical bases for further investigations into the role of kisspeptin in equine reproduction.

The use of electrochemically activated saline as a uterine instillation in pony mares : article

Twelve pony mares were randomly assigned to either a control or a treatment group and inseminated with fresh, raw semen from a single stallion of known fertility in a cross-over trial design. Pregnancy was diagnosed by transrectal ultrasound 12-14 days post-ovulation and then terminated by administration of a luteolytic dose of cloprostenol. Treatment mares received a uterine instillation of 100 ml of electrochemically activated (ECA) saline 4-12 hours post-insemination. Control mares received no treatment post-insemination. Per cycle pregnancy rate was 58.3 % in the control group and 50 % in the treatment group. There was no statistical difference (P = 1.000) in pregnancy rate between the 2 groups. The principles of ECA and applications of ECA saline are discussed.

Apparent adiposity assessed by standardised scoring systems and morphometric measurements in horses and ponies

This study described a scoring system for the assessment of apparent neck adiposity and evaluated morphometric measurements for assessment of neck and overall adiposity. Twenty-one barren Thoroughbred mares, 13 Arabian geldings and 75 Welsh, Dartmoor, or crossbred pony mares, were clinically examined and blood samples analysed for insulin, glucose, leptin, and triglycerides. Bodyweight (BW), height, length, girth and abdominal circumferences, neck length, neck crest height and neck circumference were measured, and body condition scores (BCS) and cresty neck scores (CNS) were rated. Girth:height ratio had the strongest associations with BCS ( r s = 0.64, P < 0.001 in horses; r s = 0.83, P < 0.001 in ponies) and blood variables, such as leptin ( r s = 0.39, P = 0.024 in horses; r s = 0.68, P < 0.001 in ponies). Crest height and neck circumference:height ratio had the strongest association with CNS ( r s > 0.50, P < 0.01) and blood variables, such as insulin ( r s ⩾ 0.40, P < 0.05). Cresty neck score was useful in the assessment of neck crest adiposity and had physiological relevance, as demonstrated by associations with blood variables. Girth:height was the most suitable morphometric for assessment of overall adiposity, and either crest height or neck circumference:height was a suitable morphometric for assessment of apparent neck adiposity.

Four-year contraception rates of mares treated with single-injection porcine zona pellucida and GnRH vaccines and intrauterine devices

We evaluated the multiyear contraceptive efficacy of the gonadotrophin-releasing hormone (GnRH) vaccine GonaCon, the porcine zona pellucida (PZP) vaccine SpayVac and the human intrauterine device (IUD) 380 Copper ‘T’ in mustang mares provided by the State of Nevada. Eight untreated control mares were compared with 12 mares treated with SpayVac, 16 mares treated with GonaCon and 15 mares treated with the copper-containing IUD. Rates of contraception for Years 1, 2, 3 and 4 respectively for SpayVac were 100% (12 of 12), 83% (10 of 12), 83% (10 of 12) and 83% (10 of 12), rates for GonaCon were 94% (15 of 16), 60% (9 of 15), 60% (9 of 15) and 40% (6 of 15) and rates for IUD-treated mares were 80% (12 of 15), 29% (4 of 14),14% (2 of 14) and 0% (0 of 14). Antibody titres against PZP and GnRH declined over the four-year study. For mares given SpayVac, uterine oedema was commonly observed. IUDs were visible by ultrasonography in non-pregnant mustang mares, suggesting that pregnant mares did not retain their IUD. IUD retention may be a function of uterine size: pony mares with IUDs had high retention and contraception rates for 4–5 years. We conclude that long-term contraception of mustang mares with a single shot of either the SpayVac or GonaCon vaccine is possible.

Effect of a fatty acid supplement on the estrus cycle and pregnancy rates of Brazilian Pony mares

Effect of a fatty acid supplement on the estrus cycle and pregnancy rates of Brazilian Pony mares

Passive transfer of Theileria equi antibodies to neonate foals of immune tolerant mares

Equine babesiosis, a tick transmitted haemoprotozoan disease caused by Theileria equi is globally distributed and responsible for heavy economic losses to the equine husbandry. Equids reared in endemic areas usually pick up infection at an early age and become immune tolerant throughout their life span. We studied the level of passively transferred antibodies in neonate foals born from pre-immuned mares. Latently T. equi infected pre-immuned pony and donkey mares (three each) were selected and T. equi antibody titres in neonates was monitored till 90 days post foaling (DPF) by applying Dot-ELISA on sequentially collected serum samples from foals and their dams. A very high antibody titre was observed in pre-immuned pony and donkey mares. The maximum antibody of 1:60 to 1:80 was observed in pony's and donkey's foal on 2–16 and 2–10 DPF, respectively and thereafter it declined to less than 1:20 on 63–77 and 56–63 DPF. Simultaneously parasite carrying status in neonate foals and their dam was also monitored by applying PCR on blood samples. We could demonstrate PCR amplification in dam's blood samples while no amplification was recorded in neonate's blood samples. This study indicated that new-born foals were born naïve and passively transferred immunity was transitory which wanes after 63–77 DPF.

Temporal relationships among LH, estradiol, and follicle vascularization preceding the first compared with later ovulations during the year in mares

Diameter of the preovulatory follicle, plasma concentrations of LH and estradiol, and vascularization of the follicle wall, based on color-Doppler signals, were characterized in 40 pony mares for 6 days preceding ovulation (Days −6 to −1; preovulatory period). Comparisons between the preovulatory periods preceding the first compared with a later ovulation during the year were used to study the relationships between LH and estradiol and between vascularization and estradiol. Diameter of the preovulatory follicle was greater ( P < 0.02) and concentration of LH was less ( P < 0.02) during the first preovulatory period, whereas concentration of estradiol was not different between the first and second preovulatory periods. Vascularized area (cm 2) of the follicle wall increased at a reduced rate during the first preovulatory period, as indicated by an interaction ( P < 0.03) between day and group. Vascularized area was similar between the preovulatory groups on Day −6, and a reduced rate of increase resulted in a lesser ( P < 0.001) area on Day −1 before the first ovulation (1.4 ± 0.1 cm 2) than before a later ovulation (2.2 ± 0.2 cm 2). Results demonstrated that follicle vascularization and the LH surge were attenuated preceding the first ovulation of the year with no indication that estradiol was involved in the differences between the first and later ovulations.

Continuous monitoring of penicillin G and gentamicin in allantoic fluid of pregnant pony mares by in vivo microdialysis

Most current treatments for placentitis in mares are empirical with few control studies to evaluate their effectiveness. To monitor drug concentrations in allantoic fluid of pregnant pony mares using in vivo microdialysis and establish if this method would be useful for determining allantoic concentrations of drugs in normal mares and those with placentitis. Five late gestational pony mares had microdialysis probes inserted into the allantoic fluid using transabdominal ultrasound-guided allantocentesis. Single injections of penicillin G (22,000 u/kg), gentamicin (6.6 mg/kg bwt) and flunixin meglumine (1 mg/kg bwt) were administered i.v. and dialysate samples collected continuously for 24 h. In a separate study, drug concentrations were monitored in allantoic fluid of 2 mares with experimental placentitis induced by intracervical inoculation with Streptococcus equi ssp. zooepidemicus. Drug concentrations were measured by high performance liquid chromatography (penicillin G, flunixin meglumine) or enzyme-linked immunosorbent assay (gentamicin). Penicillin G and gentamicin achieved average peak concentrations of 9.8+/-2.2 and 8.5+/-3.1 microg/ml, respectively, in allantoic fluid of noninfected mares. Pharmacokinetic comparisons indicate that penicillin G persists much longer in allantoic fluid than blood, whereas gentamicin exhibited similar profiles in the 2 compartments. Flunixin meglumine was not detected in allantoic fluid. In infected mares, penicillin G achieved a similar peak concentration in allantoic fluid (11.2 microg/ml) whereas peak gentamicin concentration (3.9 microg/ml) appeared to be reduced relative to drug concentrations in noninfected mares. Microdialysis is a useful technique for continuous in vivo monitoring of drugs in equine allantoic fluid. Our results indicate that penicillin G and gentamicin undergo effective placental transfer in pregnant mares and in 2 mares that transplacental drug transfer may be altered selectively if active placental infection is present. Further studies are needed to evaluate the feasibility of using increased dose intervals for penicillin G and an increased dose rate of gentamicin to effectively combat placental infections in mares.

Variability of plasma melatonin level in pony mares (Equus caballus), comparison with the hybrid: mules and with jennies (Equus asinus)

In long-day breeders like horses, the length of nocturnal melatonin secretion is the main messenger of photoperiod. Previous studies have shown that the nocturnal jugular melatonin concentration is lower in horses, than in mules but is unknown in donkeys. The aim of this study was to estimate the inter-animal variability of plasma melatonin concentration in domestic mares and to compare this concentration with those observed in domestic jennies and in their hybrid mules. In the autumn, blood samples were collected at 22 h, 23 h, 0 h and 1 h during 2 nights at 3 weeks intervals, in 110 pony mares, 10 jennies and 6 mules maintained under natural photoperiod. Melatonin was assayed by a validated RIA method. The statistical analysis of the measures was done with a specific unbalanced analysis of variance model. The effect of species and individuals (nested under species) was highly significant. The mean melatonin concentration was 24 pg.mL(-1) in mares and was significantly lower than in jennies and in mules which were 90 pg.mL(-1) and 169 pg.mL(-1) respectively. The melatonin plasma concentration was higher in jennies than in mares. These results suggest that the melatonin concentration is genetically determined.

Endocrine responses in mares undergoing abrupt changes in nutritional management

Leptin, a protein hormone secreted by adipocytes, plays an important role in energy homeostasis and regulation of body composition. We previously observed that acute feed restriction resulted in a rapid decline in concentrations of leptin in obese pony mares. This acute response prompted us to characterize the temporal changes in concentrations of leptin, GH, and insulin in obese pony mares during the transition between fed and feed-restricted conditions. Nine obese pony mares of mixed breed, previously maintained on fescue pasture, were randomly allotted to 2 groups. Treatments consisted of a 48-h feed restriction, a 48-h refeeding, and a 24-h feed restriction (RFR; n = 4), or 48 h of alfalfa hay ad libitum, a 48-h feed restriction, and a 24-h refeeding (FRF; n = 5). Blood samples were taken every 15 min during restriction and feeding transitions (0600 to 1400 on d 2 and 4), and every 30 min thereafter until 0830 of the following days (d 3 and 5). In the FRF treatment, plasma concentrations of leptin declined precipitously 6 h after the removal of feed (sample by treatment interaction; P < 0.01), and remained low and unresponsive to refeeding. Similarly, in the RFR group, plasma concentrations of leptin were initially low, and did not respond to feeding during the second (refeeding) sampling period. After feed restriction in each of the 2 treatment sequences, plasma insulin decreased and GH mean concentration, pulse frequency, pulse amplitude, and area under the curve increased (P < 0.05). Refeeding reversed these effects on insulin and GH. These data provide evidence that peripheral concentrations of insulin and GH are dynamically responsive to feed removal (decrease in insulin; increase in GH) and replacement (increase in insulin; decrease in GH), whereas leptin decreases in response to feed restriction but is slow to recover from a transient nutritional insult.

Acute effects of prostaglandin F 2α on systemic oxytocin and progesterone concentrations during the mid- or late-luteal phase in mares

The acute effects of prostaglandin F 2α (PGF) on circulating oxytocin and progesterone concentrations were characterized in mares during the mid- or late-luteal phase. Pony mares were randomly assigned to the following experimental groups based on treatment with PGF (2.5 mg) or saline on Day 8 or Day 13 (Day 0 = ovulation): PGF-8, PGF-13, saline-8, or saline-13 ( n = 7/group). Mares were fitted with indwelling, jugular vein catheters and two blood samples (−5 and 0 min) were collected prior to treatment. Treatments were administered into the jugular vein (0 min) and blood collection continued thereafter at 1 min intervals until 5 min and then at 5 min intervals until 60 min. Based on the combined data of −5 and 0 min samples, mares on Day 8 had greater ( P < 0.05) oxytocin concentrations than mares on Day 13. On Day 8, PGF treatment resulted in a biphasic pattern of oxytocin release. Oxytocin concentrations increased ( P < 0.05) 1 min after PGF treatment, decreased ( P < 0.05) from 1 to 10 min, and increased ( P < 0.05) from 10 to 30 min. Oxytocin concentrations were greater ( P < 0.05) from 1 to 3 min in PGF-treated than saline-treated mares and at most sample times from 15 to 60 min. On Day 13, oxytocin concentrations were greater ( P < 0.05) in PGF-treated than in saline-treated mares for most sample times. Mares treated with PGF on Day 8 had greater ( P < 0.05) oxytocin concentrations at 25, 30, and 40 min than mares on Day 13. Progesterone concentrations on Day 8 also increased by 1 min after PGF, decreased toward basal concentrations by 2–3 min, and then increased to a maximum 10 min after treatment. Subsequently, circulating progesterone decreased ( P < 0.05) below pretreatment concentrations by 40–50 min after PGF. In conclusion, treatment with PGF resulted in an immediate and biphasic increase in progesterone concentrations prior to the expected decrease. Treatment of mares with PGF on Day 8 resulted in an overall greater increase in systemic oxytocin concentrations compared to treatment on Day 13, and the increase on Day 8 was biphasic.

Real-time ultrasound measure of the fetal eye (vitreous body) for prediction of parturition date in small ponies

Ultrasonographic fetal eye measures have been used to estimate gestational age of the fetus in light horse mares. However, fetal eye measures have not been published for smaller pony breeds. This study was conducted to develop reference ranges for ultrasonographic measures of fetal eyes in small ponies for the purpose of predicting days before parturition (DBP) when breeding or ovulation dates are unknown. Twenty-three Shetland-type pony mares were studied across one ( n = 10) or two ( n = 13) gestations in 2004 (18 pregnancies) and 2005 (18 pregnancies). Measurements of fetal eyes were obtained during transrectal ultrasound examination. Examinations were conducted once monthly in a field situation beginning in December (2003) or August (2004) until mares foaled (March through July). The length (from sclera to sclera) and width (from retina to cornea) of the vitreous body were measured. For the 273 examinations in which gestation age was greater than 2 months, eye measures were obtainable in 248 (91%). Mixed-effects linear regression modeling was used to account for serial growth measures within pregnancy, repeated measurements across mares, and unbalanced study design. Independent variables evaluated included vitreous body length, vitreous body width, the ratio of length to width, parity, and mare height at the withers at parturition. Eye length was the best single predictor of days before parturition, with almost no additional predictive value of the other variables considered. Our resulting regression equation is: days before parturition = 265.16 − 0.21*(vitreous body length in mm) 2 . This study suggests that measure of the fetal eye is a practical on-farm procedure for estimating days before parturition in small ponies.

91 PRELIMINARY RESULTS OF SURGICAL EQUINE EMBRYO TRANSFER AFTER OPEN PULLED STRAW VITRIFICATION

In equine species, embryo cryopreservation is not as widely developed as in some other species. Slow freezing has been applied to equine embryos but with relatively low success rates. This higher sensitivity to conventional freezing procedures may be explained by the presence of a capsule surrounding the equine embryo that may impair cryoprotectant penetration. Recently, good in vitro embryo survival rate was obtained after open pulled straw (OPS) vitrification (Moussa et al. 2005 Theriogenology 64, 1619–1632). The aim of the present study was to evaluate in vivo survival of vitrified embryos five days after surgical transfer into Welsh pony mares. Morulae (M), early blastocysts (EB), and blastocysts (B) ranging from 140 to 320 μm in diameter were collected (n = 20) in a Ringer lactate solution on Day 6.75 after ovulation. Before vitrification, embryos were assessed morphologically and their size was measured (McKinnon and Squires 1988 J. Am. Vet. Med. Assoc. 192, 401–406). Then, embryos were vitrified using the OPS method described by Berthelot et al. (2001 Reprod. Nutr. Dev. 41, 267–272). Briefly, embryos were washed twice in HEMES-TCM-199 + 20% newborn calf serum (NBCS) for 1 min, equilibrated in HEPES-TCM-199 + 20% NBCS with 7.5% dimethyl sulfoxide (DMSO) + 7.5% ethylene glycol (EG) for 3 min, and then with 18% DMSO + 18% EG + 0.4 M sucrose for 45 s. One embryo was then loaded per straw. For transfer, four straws were quickly thawed (5 s in air) and the narrow end of the straw containing the embryo was immersed in HEPES-TCM-199 + 20% NBCS + PBS + 0.2 M sucrose. Five to 8 min after thawing, four embryos were surgically transferred into the cranial portion of the uterine horn in each of five pony mare recipients. Five days after transfer, embryos recovered by transcervical flushing of the uterus were classified as viable if morphology was normal, no dark inner cells were present, the capsule was intact, and the diameter was at least 1000 μm. The results are shown in the table. One recipient of vitrified embryos had an endometritis and no embryo was recovered. From the four other recipients, nine embryos were recovered out of 16 (56%) transferred, seven of which were viable (44%). The results of the present preliminary study demonstrating survival of equine embryos transferred after OPS vitrification is very encouraging. However, the results should be confirmed by birth of foals after transfer of OPS-vitrified embryos to recipients. Table

Functional Morphology of Equine Pre‐ovulatory Cumulus‐oocyte Complexes

Knowledge of the functional morphology of equine cumulus‐oocyte‐complexes (COCs) shortly before ovulation is scarce. Therefore the aim of our studies was to characterize COCs matured in vivo by light microscopy, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and immunohistochemistry (ICC). Pre‐ovulatory COCs were obtained by ultrasound‐guided transvaginal aspiration of pre‐ovulatory follicles of 26 pony mares. The morphology of pre‐ovulatory COCs was compared to that of immature COCs obtained by slicing of ovaries from the slaughterhouse. As shown by light microscopy and SEM, immature COCs possess numerous round, densely packed cumulus cells, which contact each other and possess merely single short processes. Contrary, in pre‐ovulatory oocytes the cumulus cells are widely separated but send long cytoplasmic processes to the zona pellucida (ZP). All the cumulus cells are embedded in a huge amount of homogenous extracellular matrix. As shown by alcian blue staining and Periodic Acid Schiff Reaction (PAS) with and without amylase digestion, this matrix contains glycoproteins and acidic and sulphated glycosaminoglycans. In pre‐ovulatory COCs both the oocyte and the cumulus cells produce glycosaminoglycans, whereas immature COCs are negative for alcian blue. Similarly, glycoproteins are synthesized in pre‐ovulatory, but not in immature COCs. As shown by ICC, hyaluronic acid is one of the most abundant mucopolysaccharide in the pre‐ovulatory COC. The high synthetic activity of the cumulus cells in the pre‐ovulatory COC is confirmed by TEM showing densely packed endoplasmic reticulum (ER) and accumulation of glycogen in the cumulus cells. Our results imply that in the equine in vitro maturation of the oocyte is characterized by the cumulus cells synthesizing an extracellular matrix of glycoproteins and acidic and sulphated glycosaminoglycans. The extensive production of extracellular, water‐binding matrix in the pre‐ovulatory COC ensures mechanical protection and nutrition of the oocyte.

Variation in Plasma Adrenocorticotropic Hormone Concentration and Dexamethasone Suppression Test Results with Season, Age, and Sex in Healthy Ponies and Horses

The purpose of this study was to evaluate the variation in plasma adrenocorticotropic hormone (ACTH) concentration and dexamethasone suppression test (DST) results with season, age, and sex in healthy, pony mares (n = 15)and pony stallions (n = 14) living under semiferal conditions and horse mares (n = 10) living at pasture. Plasma ACTH concentrations were measured in September 2002, and in January, May, and September 2003. DSTs were performed in January and September 2003. Plasma ACTH concentrations in September 2002 and September 2003 were similar and were significantly greater than in January and May (P .05). Seasonal changes in plasma ACTH concentration and DST results should be considered when interpreting endocrine test results.

Variation in Plasma Adrenocorticotropic Hormone Concentration and Dexamethasone Suppression Test Results with Season, Age, and Sex in Healthy Ponies and Horses

The purpose of this study was to evaluate the variation in plasma adrenocorticotropic hormone (ACTH) concentration and dexamethasone suppression test (DST) results with season, age, and sex in healthy, pony mares (n=15) and pony stallions (n=14) living under semiferal conditions and horse mares (n=10) living at pasture. Plasma ACTH concentrations were measured in September 2002, and in January, May, and September 2003. DSTs were performed in January and September 2003. Plasma ACTH concentrations in September 2002 and September 2003 were similar and were significantly greater than in January and May (P < .001). Plasma ACTH concentration was within the reference range for 38 (97%) of 39 subjects in January, for 39 (100%) of 39 subjects in May, for 2 (5%) of 39 subjects in September 2002, and for 3 (8%) of 39 subjects in September 2003. DST results were within the reference range in all subjects in January and were within the reference range for 29 (74%) of 39 subjects in September 2003. Plasma cortisol concentration at the end of the DST was significantly greater in September than in January (P = .002). Age was positively correlated with plasma ACTH and plasma cortisol concentration at the beginning and end of the DST Within the same season, plasma ACTH concentration in pony mares, pony stallions, and horse mares was not significantly different (P > .05). Seasonal changes in plasma ACTH concentration and DST results should be considered when interpreting endocrine test results.