Reproduction In Mares Research Articles

Effects of Nitrate and Pathogenic Nanoparticles on Reproductive Losses, Congenital Hypothyroidism and Musculoskeletal Abnormalities in Mares and Other Livestock: New Hypotheses

Spontaneous abortions, congenital hypothyroidism and musculoskeletal abnormalities were attributed to high nitrate in the diet of pregnant mares on Thoroughbred farms in central Kentucky. These fetal losses, with an unknown etiology, and associated with the Mare Reproductive Loss Syndrome (MRLS) have plagued horse farms in central Kentucky for decades. Fetal losses occur in mares grazing spring pastures affected by climatic and environmental factors including droughts, cold-stress, nitrogenous fertilizers, and herbicides. These factors may cause nitrate to accumulate in pasture forages. On a Thoroughbred horse farm, mares affected with the MRLS, pregnant Boer goats grazing high nitrate pastures also were affected with fetal losses. When spring pastures were not fertilized with nitrogen, herbicides not applied, protein reduced in the ration and the diet increased in sodium, fetal losses did not occur and foals were normal at birth. Excessive nitrate, ammonia and sulfate in the diet were associated with the formation of toxic and pathogenic abiotic nanoparticles in the amnionic fluid and pathognomonic placental lesions consistent with the MRLS. Pathogenic nanoparticles were found in aborted fetuses of other livestock. The discovery of these toxic pathogenic abiotic micro and nanoparticles in developing fetuses is unique. This novel mechanism of action for the pathogenesis of fetal losses may be a predisposing factor for a host of opportunistic diseases in livestock. The pathogenic nanoparticles collect in the vessels of the placenta and other organs to form niduses that predispose fetuses to a host of opportunistic microorganisms.

Coumestrol and its metabolite in mares' plasma after ingestion of phytoestrogen-rich plants: Potent endocrine disruptors inducing infertility

Phytoestrogens exist in plants that are present in forages fed to horses. They may compete with 17-β estradiol and influence the estrous cycle. Therefore, the objective was to determine whether coumestrol from clover-mixed pastures is present in mare's plasma after their ingestion (experiment I), and when this phytoestrogen was present in mare's plasma after ingestion (experiment II). The effect of a long-term ingestion of phytoestrogens on estrous cycle disruption was assessed (experiment III; clinical case). Experiment I was carried out in nonpregnant anestrous and cyclic Lusitano mares (n = 14) kept on clover and grass-mixed pastures, and supplemented with concentrate and hay or cereal straw. Blood and feedstuff were obtained from November to March. In experiment II, stabled cyclic Lusitano mares (n = 6) were fed for 14 days with increasing amounts of alfalfa pellets (250 g to 1 kg/day). Sequential blood samples were obtained for 8 hours after feed intake on Day 0 (control) and on Days 13 and 14 (1 kg/day alfalfa pellets). Experiment III mares were fed with a mixture of alfalfa and clover haylage for 5 months (group 1; n = 4) or for 9 months (group 2; n = 12). Estrous cycle was determined on the basis of plasma estradiol (E2), progesterone (P4), and ultrasound (experiment III). Concentrations of phytoestrogen coumestrol and its metabolite methoxycoumestrol were determined by high-performance liquid chromatography coupled with mass spectrometry. Phytoestrogens decreased in pasture from November until March (P < 0.01) (experiment I), but were always detected in mares' plasma. In experiment II, plasma-conjugated forms of coumestrol and methoxycoumestrol were higher on Days 13 and 14 than in control (P < 0.05). The highest concentrations of conjugated form of coumestrol were at 1.5 and 4 hours (P < 0.001), whereas its free forms peaked at 1 and at 3.5 hours after ingestion (P < 0.05). Methoxycoumestrol-conjugated form concentration was the highest at 1.5 and 5 hours (P < 0.001), whereas its free form peaked at 1 hour (P < 0.05) and at 1.5 hours (P < 0.001). Long-term intake of coumestrol caused lack of ovulation, uterine edema, and uterine fluid accumulation (experiment III). Coumestrol and methoxycoumestrol in both forms were higher in group 2 (while still ingesting haylage) than in group 1, after haylage withdrawal (P < 0.001). These data show that in the mare, coumestrol and its metabolite increase in blood after ingestion of estrogenic plants and can influence reproduction in mares as potent endocrine disruptors.

Prevalence of Yeasts in English Full Blood Mares

The aim of the study was a quantitative and qualitative analysis of microflora, presentation of current data about prevalence of the microflora on the skin and mucous membranes, and determination of its possible effect on reproduction of English full blood horses bred in Poland. The material for analyses was sampled from the skin and mucous membranes (385 samples) of 55 English full blood mares. Taking into account reproduction traits, the mares were classified into three groups. Six yeast-like species, including five species from the genus Candida (C. albicans, C. guiliermondii, C. lusitaniae, C. sp., and C. tropicalis) and Trichomonascus ciferrii, were detected on the skin and mucous membranes in the English full blood mares. Growth of yeasts was observed in more than half of the samples taken from mares that had foaled and approximately 46 % of non-conceiving and barren mares. The high prevalence of various yeast strains in the mouth, nostrils, and collateral groove may suggest widespread occurrence of the microflora in the breeding environment. The results obtained indicate that the yeasts isolated in this study may be components of the normal microflora of the skin and mucous membranes in horses. The analysis results do not indicate unambiguously that the isolated microflora affects reproduction in mares, although this cannot be excluded.

Retrospective and statistical analysis of breeding management on the Italian Heavy Draught Horse breed

This study investigated some aspects of breeding management in the Italian Heavy Draught Horse breed, aiming at improving its efficiency at stud farm level. A first aim was to evaluate the risk of unsuccessful reproduction in mares after an early (3 years) or normal (4 years) age at first foaling, in interaction with different stud rearing systems. A second objective was the examination of the mean time length in which young 2-year-old stallions maintain a genetic superiority on older proven stallions, identifying a ‘genetic lifespan’ in which young stallions can be safely used for reducing the cost of services. Reproductive performance at first and second foaling of 1513 mares were used. Mares had a normal first foal at 3 (n = 745) or 4 years of age (n = 768) in stud farms on the basis of stable (n = 488), feral (n = 345) or semi-feral (n = 680) rearing systems. Logistic regression analysis was performed by modeling the risk of unsuccessful reproduction in the subsequent season (i.e., results at second foaling), as affected by the interaction of age at first foaling × rearing system (six classes). Genetic lifespan of young stallions was estimated by regressing the least square means from a mixed model analysis for repeated measures of individual differences in ‘total merit’ estimated breeding values (EBVs) between young stallions (mean no. of 45/year) and the mean EBV of all proven stallions in a given year of genetic evaluation (mean no. of 483/year). Young stallions born between 1999 and 2005 were used, following each generation (i.e., birth year) from 2 to 7 subsequent yearly genetic evaluations. In comparison with the best reproductive success of second foaling at 4 years in stable systems, the greatest risk of unsuccessful reproduction was at 3 years in feral (+167%) and 3 years in semi-feral conditions (+91%). Young stallions showed a 0.50 s.d. greater EBV at the first evaluation than proven stallions, with a mean annual decrease in EBV of 0.07 s.d./year on proven stallions. Optimal breeding management could be obtained in stud farms by limiting foaling at 3 years, particularly in feral and semi-feral rearing systems, and using young stallions for 3 to 4 years to maintain a perceptible selection differential with older proven stallions and to reduce cost of services. Later, the selection differential with proven stallions become less consistent and genetic improvement could be slowed down.

Nocardioform placentitis in Australia with implications for Equine Amnionitis and Foetal Loss (EAFL) and Mare Reproductive Loss Syndrome (MRLS)

Nocardioform placentitis in Australia with implications for Equine Amnionitis and Foetal Loss (EAFL) and Mare Reproductive Loss Syndrome (MRLS)

Age of the Jeju pony (Equus caballus) at first reproduction: potential costs for foals and mothers that first reproduce early in life

In a related paper, we showed that mares that reproduced early in life tended to have higher fecundity because of a decrease in the duration of inter-birth intervals relative to mares that reproduced later in life. However, we know that young mares are subordinate to older mares. Hence, costs associated with low dominance rank might offset the benefits of earlier reproduction. We compared harassment of foals of female Jeju ponies that first reproduced at three years of age with that of foals of females that first reproduced at five years of age. As a consequence of their positions in the linear dominance hierarchy, foals born to and guarded by young mares were harassed more frequently than foals whose mothers were older when they first reproduced. A mare that reproduced early in life guarded her offspring more closely and intervened between her foal and neighboring mares more frequently than those mares which first reproduced when older. This need to guard their foals and the harm that might ensue from frequent harassment might counter-balance selection towards earlier reproduction in mares.

Hormone Profiles of Mares Affected by the Mare Reproductive Loss Syndrome

While searching for the cause of the Mare Reproductive Loss syndrome (MRLS), we postulated that 1 of 3 tissues in 40-120 D pregnant mares was the likely primary target of the noxious factor that caused early abortions: The corpora lutea (CL), the endometrium or the fetus and/or its membranes. At this stage of gestation, progesterone (P4) is solely produced by luteal tissue, eCG by endometrial cups in the endometrium and oestrogens by the feto-placental unit. We determined whether concentrations of P4, eCG and/or total conjugated oestrogens (CE) would indicate which tissue was targeted during the MRLS. P4, eCG and CE were measured in single serum samples collected from 216 mares, 60-110 D after ovulation during the 2001 MRLS outbreak. All mares had previously been confirmed pregnant by ultrasonography. The following data was obtained from each mare: Interval from ovulation, pregnancy status and normalcy of fetal fluids at the time of sampling, and pregnancy status 3 weeks after sampling and at term. There were no meaningful differences in hormone concentrations between pregnant mares that had normal and excessively echogenic fetal fluids at the time of sampling. CE were lower (p < 0.05) in mares that aborted after sample collection than in mares the carried to term. In 8 mares from which multiple samples were obtained, CE consistently decreased prior to any decreases in P4 or eCG. Arguments are presented that lead to the hypothesis that the fetal trophoblast was the primary target of the MRLS agent.

Epidemiological study with the mare and Neotyphodium coenophialum toxins

The objective of this study was to relate chemical components of pastures containing tall fescue suspected to be causative to reduced conception and early embryonic death in the mare. Pasture sampling was conducted on 143 pastures and over 500 sites during mare breeding. Tall fescue was 16- 42% of the forage in most pastures and about 65% of the plants were infected with Neotyphodium coenophialum. Ergovaline content ranged from 0 to 2220 ng/g. Lysergic acid was present in equal or lesser amounts than ergovaline. Approximately 10% of the mares did not conceive or had early foetal loss. Because of other components in the diet, a direct cause/effect relationship cannot be made between mare response and N. coenophialum related toxins. These results suggest that a large number of animals will be required when designing an experiment to show how tall fescue might affect reproduction in mares. Keywords: horse pastures, alkaloids, minerals

A Murine model of Mare Reproductive Loss Syndrome

Background Mare reproductive loss syndrome (MRLS), first reported in 2001 from Kentucky, has caused thousands of equine abortions and estimated $1/2 billion in economic loss. MRLS affects mare after ingesting caterpillars. This may result in irritation, lesions and increased gut permeability. The á hemolytics Strep. sp and Actinobacillus sp, present in normal digestive tract, have been isolated in field and experimental aborted cases. Bacterial replication in the fetal fluids is likely to compromise the fetus and causes abortion. A murine model would facilitate the study of MRLS. Methods Seventy programmed pregnant ICR mice were injected via tail vein or IP with 1X104–8 CFU Strep. cricetus and/or Actinobacillus sp isolated from aborted fetus. Control animals received saline. Results Injected dams did not develop any clinical symptoms. There were sporadic cases of aborted fetuses that correlated with the amount of bacteria. No significant difference was noted between the number of delivered pups and their weight between groups. Day old pups when injected with bacteria developed focal abscess, lost weight but recovered after one week. However, SRA/CD36 deficient pregnant mice developed 100% fetal death and abortion 24–74h after bacterial injection. We conclude that deficient mice may serve as a pivotal model to study MRLS.

The Toxicokinetics of Cyanide and Mandelonitrile in the Horse and Their Relevance to the Mare Reproductive Loss Syndrome

The epidemiological association between black cherry trees and mare reproductive loss syndrome has focused attention on cyanide and environmental cyanogens. This article describes the toxicokinetics of cyanide in horses and the relationships between blood cyanide concentrations and potentially adverse responses to cyanide. To identify safe and humane blood concentration limits for cyanide experiments, mares were infused with increasing doses (1-12 mg/min) of sodium cyanide for 1 h. Infusion at 12 mg/min produced clinical signs of cyanide toxicity at 38 min; these signs included increased heart rate, weakness, lack of coordination, loss of muscle tone, and respiratory and behavioral distress. Peak blood cyanide concentrations were about 2500 ng/mL; the clinical and biochemical signs of distress reversed when infusion stopped. Four horses were infused with 1 mg/min of sodium cyanide for 1 h to evaluate the distribution and elimination kinetics of cyanide. Blood cyanide concentrations peaked at 1160 ng/mL and then declined rapidly, suggesting a two-compartment, open model. The distribution (alpha) phase half-life was 0.74 h, the terminal (beta phase) half-life was 16.16 h. The mean residence time was 12.4 h, the steady-state volume of distribution was 2.21 L/kg, and the mean systemic clearance was 0.182 L/h/kg. Partitioning studies showed that blood cyanide was about 98.5% associated with the red cell fraction. No clinical signs of cyanide intoxication or distress were observed during these infusion experiments. Mandelonitrile was next administered orally at 3 mg/kg to four horses. Cyanide was rapidly available from the orally administered mandelonitrile and the C max blood concentration of 1857 ng/mL was observed at 3 min after dosing; thereafter, blood cyanide again declined rapidly, reaching 100 ng/mL by 4 h postadministration. The mean oral bioavailability of cyanide from mandelonitrile was 57% ± 6.5 (SEM), and its apparent terminal half-life was 13 h ± 3 (SEM). No clinical signs of cyanide intoxication or distress were observed during these experiments. These data show that during acute exposure to higher doses of cyanide (~600 mg/horse; 2500 ng/mL of cyanide in blood), redistribution of cyanide rapidly terminated the acute toxic responses. Similarly, mandelonitrile rapidly delivered its cyanide content, and acute cyanide intoxications following mandelonitrile administration can also be terminated by redistribution. Rapid termination of cyanide intoxication by redistribution is consistent with and explains many of the clinical and biochemical characteristics of acute, high-dose cyanide toxicity. On the other hand, at lower concentrations (<100 ng/mL in blood), metabolic transformation of cyanide is likely the dominant mechanism of termination of action. This process is slow, with terminal half-lives ranging from 12-16 hours. The large volume of distribution and the long terminal-phase-elimination half-life of cyanide suggest different mechanisms for toxicities and termination of toxicities associated with low-level exposure to cyanide. If environmental exposure to cyanide is a factor in the cause of MRLS, then it is likely in the more subtle effects of low concentrations of cyanide on specific metabolic processes that the associations will be found.

Age at puberty, cyclicity, clinical response to PGF2α, hCG and GnRH and embryo recovery rate in yearling mares

This study investigated some aspects of breeding management in the Italian Heavy Draught Horse breed, aiming at improving its efficiency at stud farm level. A first aim was to evaluate the risk of unsuccessful reproduction in mares after an early (3 years) or normal (4 years) age at first foaling, in interaction with different stud rearing systems. A second objective was the examination of the mean time length in which young 2-year-old stallions maintain a genetic superiority on older proven stallions, identifying a ‘genetic lifespan’ in which young stallions can be safely used for reducing the cost of services. Reproductive performance at first and second foaling of 1513 mares were used. Mares had a normal first foal at 3 (n = 745) or 4 years of age (n = 768) in stud farms on the basis of stable (n = 488), feral (n = 345) or semi-feral (n = 680) rearing systems. Logistic regression analysis was performed by modeling the risk of unsuccessful reproduction in the subsequent season (i.e., results at second foaling), as affected by the interaction of age at first foaling × rearing system (six classes). Genetic lifespan of young stallions was estimated by regressing the least square means from a mixed model analysis for repeated measures of individual differences in ‘total merit’ estimated breeding values (EBVs) between young stallions (mean no. of 45/year) and the mean EBV of all proven stallions in a given year of genetic evaluation (mean no. of 483/year). Young stallions born between 1999 and 2005 were used, following each generation (i.e., birth year) from 2 to 7 subsequent yearly genetic evaluations. In comparison with the best reproductive success of second foaling at 4 years in stable systems, the greatest risk of unsuccessful reproduction was at 3 years in feral (+167%) and 3 years in semi-feral conditions (+91%). Young stallions showed a 0.50 s.d. greater EBV at the first evaluation than proven stallions, with a mean annual decrease in EBV of 0.07 s.d./year on proven stallions. Optimal breeding management could be obtained in stud farms by limiting foaling at 3 years, particularly in feral and semi-feral rearing systems, and using young stallions for 3 to 4 years to maintain a perceptible selection differential with older proven stallions and to reduce cost of services. Later, the selection differential with proven stallions become less consistent and genetic improvement could be slowed down.

Induction of ovulation and superovulation in mares using equine LH and FSH separated by hydrophobic interaction chromatography

Pharmacological control of reproduction in mares requires the use of equine gonadotrophins to avoid induced immunological resistance. Crude equine gonadotrophins (CEG) have been used but the presence of equine luteinizing hormone (eLH) and follicle-stimulating hormone (eFSH) in CEG has led to disappointing results in superovulation studies. Separation of eLH and eFSH activities from CEG is necessary to overcome this problem. The hydrophobic properties of the two hormones were sufficiently different to permit their separation by hydrophobic interaction chromatography (HIC) on a phenyl Sepharose matrix. Good yields of separate FSH and LH fractions were readily obtained by stepwise elution and the method was adapted for large scale preparations of enriched fractions of eLH and eFSH. Two experiments were performed in vivo to evaluate the biological activity of the HIC fractions. Experiment 1 showed that biological activity of the LH fraction in inducing ovulation of preovulatory follicles was similar to that obtained with CEG, indicating that LH bioactivity was not altered by HIC. Experiment 2 demonstrated that biological activity of the FSH fraction was identical (as far as rate of ovulation was concerned) to that of CEG in superovulating mares, indicating that FSH activity was also not altered by HIC. Although we have not obtained better results with the separate equine gonadotrophins than with CEG, it is potentially advantageous to use preparations with single activity to obtain a controlled balance of FSH and LH activity. The HIC technique was chosen because it could easily be scaled up to provide the large amounts of the separate hormones needed for the treatment of a large number of mares.

Effect of selenium and endophyte-contaminated fescue on performance and reproduction in mares

Sixteen gravid mares were used in a 2 × 2 factorial arrangement of treatments. The four main effects groups were: selenium (S), no selenium (NS), endophyte fescue (E) and endophyte-free fescue (NE). Mares grazed either E or NE pastures from late fall until parturition in early spring. Each mare was injected with selenium (2.5 mg/45 kg body weight) in the form of sodium selenite or the vehicle at 28 day intervals. The mares were weighed, body condition scored, and blood samples and temperatures were taken initially, every 28 days on test and at parturition. Additional measurements taken at parturition were foal weight and placental weight. Colostrum samples were taken at parturition and placental samples were taken from the nonfunctional horn portion of the placenta for determinations of thickness, stress and strain. Gestation length was 360 and 333 days (P<.01) for E and NE mares, respectively. A greater number of mares (71%) grazing E pasture had retained placentas (P<.01) and agalactia (88%, P<01). There was no effect of endophyte on the placental stress value (P>.05), but there was an effect of endophyte on strain (P<.05). Serum prolactin levels were lower (P<.01) for E mares at parturition (16.1 and 51.6 ng/ml for E and NE, respectively) and throughout gestation. Progesterone and estrogen levels were also lower (P<.05) for E mares at foaling. Selenium had no effect on any of the parameters measured (P>.05), and there were no selenium x endophyte interactions (P>.05). These data suggest that endophyte fescue is highly toxic to gravid mares.

Mycotic endometritis in mares review and clinical observations

Abstract Extract Mycotic infections of the nonpregnant equine uterus have become more frequent with the widespread use of antibiotics and the increasingly intensive management and manipulation of reproduction in mares. Although fungi and yeasts have often been blamed for uterine infection, their precise relations to clinical uterine disease are often unclear. These organisms are common in the environment and their recovery in routine culture swabs from mares' uteri may be considerably more frequent than their involvement in the aetiology of uterine disease.

Hormone Therapy for Control of Reproduction in Mares and Stallions

Because the reproductive performance of mares is lower than that of any other domesticated species, hormone therapy is important in ensuring fertility and proper management of pregnancy. Current techniques of hormone therapy are discussed.

Characteristics of Postpartum Reproduction in Mares

Characteristics of Postpartum Reproduction in Mares

Researches on Reproduction in Mares

Researches on Reproduction in Mares