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Pony Mares (pony + mare)

Distribution by Scientific Domains
Life Sciences50%

Selected Abstracts

24-Hour Secretion Patterns of Plasma Oestradiol 17, in Pony Mares in Late Gestation

REPRODUCTION IN DOMESTIC ANIMALS, Issue 3 2003
LJ O'Donnell
Contents The mare exhibits nocturnal uterine contractions in the last 6 days of gestation. It is hypothesized that estradiol 17, (O17,) may be associated with the nightly increase in uterine contractions. The 24-h secretion pattern of plasma O17, was measured in 3 pony mares in late gestation to identify changes in release as the mare neared parturition. Blood was collected weekly at 08:00 hours beginning on day 240 and every third day from day 330 until delivery. Serial blood samples were collected from each mare every 30-min for 24-h beginning on gestation day 310 and every sixth day thereafter until parturition. Concentrations of O17, were elevated at night with lowest concentrations occurring directly before sunset (p < 0.01). The natural log of the variance was increased at sunset (p < 0.01) and was decreased during the 6-h period immediately after sunrise. This pattern was especially evident in the 6 days that preceded parturition. The contrast between nocturnal and daytime concentrations of O17, in the last 6 days of gestation may contribute to night-time delivery in the mare. [source]

Development of cardiovascular function in the horse fetus

THE JOURNAL OF PHYSIOLOGY, Issue 3 2005
Dino A. Giussani
In mammals, the mechanisms regulating an increase in fetal arterial blood pressure with advancing gestational age remain unidentified. In all species studied to date, the prepartum increase in fetal plasma cortisol has an important role in the maturation of physiological systems essential for neonatal survival. In the horse, the prepartum elevation in fetal cortisol and arterial blood pressure are delayed relative to other species. Hence, the mechanisms governing the ontogenic increase in arterial blood pressure in the horse fetus may mature much closer to term than in other fetal animals. In the chronically instrumented pony mare and fetus, this study investigated how changes in fetal peripheral vascular resistance, in plasma concentrations of noradrenaline, adrenaline and vasopressin, and in the maternal-to-fetal plasma concentration gradient of oxygen and glucose relate to the ontogenic changes in fetal arterial blood pressure and fetal plasma cortisol concentration as term approaches. The data show that, towards term in the horse fetus, the increase in arterial blood pressure occurs together with reductions in metatarsal vascular resistance, elevations in plasma concentrations of cortisol, vasopressin, adrenaline and noradrenaline, and falls in the fetal : maternal ratio of blood P and glucose concentration. Correlation analysis revealed that arterial blood pressure was positively related with plasma concentrations of vasopressin and noradrenaline, but not adrenaline in the fetus, and inversely related to the fetal : maternal ratio of blood P, but not glucose, concentration. This suggests that increasing vasopressinergic and noradrenergic influences as well as changes in oxygen availability to the fetus and uteroplacental tissues may contribute to the ontogenic increase in fetal arterial blood pressure towards term in the horse. [source]

24-Hour Secretion Patterns of Plasma Oestradiol 17, in Pony Mares in Late Gestation

REPRODUCTION IN DOMESTIC ANIMALS, Issue 3 2003
LJ O'Donnell
Contents The mare exhibits nocturnal uterine contractions in the last 6 days of gestation. It is hypothesized that estradiol 17, (O17,) may be associated with the nightly increase in uterine contractions. The 24-h secretion pattern of plasma O17, was measured in 3 pony mares in late gestation to identify changes in release as the mare neared parturition. Blood was collected weekly at 08:00 hours beginning on day 240 and every third day from day 330 until delivery. Serial blood samples were collected from each mare every 30-min for 24-h beginning on gestation day 310 and every sixth day thereafter until parturition. Concentrations of O17, were elevated at night with lowest concentrations occurring directly before sunset (p < 0.01). The natural log of the variance was increased at sunset (p < 0.01) and was decreased during the 6-h period immediately after sunrise. This pattern was especially evident in the 6 days that preceded parturition. The contrast between nocturnal and daytime concentrations of O17, in the last 6 days of gestation may contribute to night-time delivery in the mare. [source]

Functional Morphology of Equine Pre-ovulatory Cumulus-oocyte Complexes

ANATOMIA, HISTOLOGIA, EMBRYOLOGIA, Issue 2005
S. Kölle
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. [source]