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Topic:Mares
Mares and horses are integral components of equine studies, focusing on the reproductive and behavioral aspects of equine biology. Mares, or adult female horses, play a significant role in breeding programs and are often studied for their reproductive physiology, gestation, and maternal behaviors. Horses, as a broader category, encompass both sexes and all age groups, providing a comprehensive view of equine anatomy, physiology, and behavior. Research in this area often investigates the differences and similarities between mares and other horses in terms of hormonal cycles, reproductive health, and social interactions. This page compiles peer-reviewed studies and scholarly articles that explore the biological and behavioral characteristics of mares and horses, offering insights into their roles in equine science and management.
Xylazine causes transient dose-related hyperglycemia and increased urine volumes in mares. Xylazine given IV at doses of 0.5, 1.0, and 1.5 mg/kg to mares caused a significant (P less than 0.05) dose-related increase in serum glucose concentration and urine volume. Serum glucose concentrations as much as 150 mg/dl were recorded in mares after they were given the largest xylazine dose. The greatest urine volume, similar to changes in peak glucose concentration, always occurred during the first hour after dosing with xylazine and averaged 1.82, 3.93, and 5.68 ml/kg/hour after the 0.5-, 1.0-, and 1.5-mg/kg doses, respectively, were given. Urine osmolality and specific gravity were signi...
Androstenedione and testosterone biosynthesis by the adrenal cortex of the horse. An homogenate from cortical tissue of mare adrenals was incubated in the presence of tritiated pregnenolone. The (3H) androstenedione and the (3H) testosterone synthesized during the incubation were extracted, purified, and co-crystallized to constant specific activity in the presence of unlabeled carriers. The rate of conversion of pregnenolone to androstenedione and testosterone was of the order of 5 and 0.15 per cent respectively. The high ratio of (3H) androstenedione to (3H) testosterone observed in this study suggests that androstenedione is the main androgen produced by mare adrenals. I...
Effect of exogenous gonadal steroids and pregnancy on uterine luminal prostaglandin F in mares. Two experiments were conducted to assess the effect of exogenous hormone treatment on uterine luminal prostaglandin F (PGF). In the first experiment ovariectomized pony mares received either corn oil (21 days, n = 3), estradiol valerate (21 days, n = 3), progesterone (21 days, n = 3) or estradiol valerate (7 days) followed by progesterone (14 days, n = 4). Progesterone treated mares had higher (P less than .01) uterine luminal PGF compared with all other groups, and no differences were detected between other treatment comparisons. In Experiment II, uterine fluid was collected from 4 ovariectom...
Ultrasonography as an adjunct to pregnancy assessments in the mare. Ultrasonographic detection of pregnancy was performed in 952 Thoroughbred mares. Characteristic images were obtained between 12 and 55 days after breeding. Twins in the same uterine horn as well as twins in opposite horns were imaged, and for the first few months of gestation appeared similar to single pregnancies. Growth curves as a function of time were developed, utilizing horizontal diameters of the blastocysts versus breeding dates. Comparisons between horizontal and vertical diameters demonstrated no appreciable differences when observed as a group. Growth curves derived from twins did n...
Effect of stage of cycle, sampling frequency and recovery of micro-organisms on total protein content of mare uterine flushings. Mares with sound reproductive tracts were divided into two groups. In Group I (N = 12), uteri were flushed once per oestrous cycle during alternate cycles while in Group II (N = 8) mares were flushed twice in a cycle for 2 contiguous cycles. Total protein concentrations and total recoverable protein of uterine flushings taken on Day 3 of oestrus and Day 8 after ovulation in each of the 2 groups and between the 2 groups did not differ significantly. The length of oestrus and dioestrus was not affected by the flushing procedures. Total recoverable protein and total protein concentrations of flus...
Times of appearance and disappearance of colostral IgG in the mare. Pre- and postpartum colostral samples collected from 14 Arabian and 22 Thoroughbred mares were examined for color, consistency, and immunoglobulin (Ig)G concentration. Initial samples, obtained 3 to 28 days before mares had foaled, contained greater than 1,000 mg of IgG/dl. Mean concentration of IgG in colostrum of the Arabian mares at the time of parturition (T0) was 9,691 mg/dl and was significantly (P less than 0.05) higher than the average, 4,608 mg/dl, for the Thoroughbreds. Average times lapsed from T0 until the colostral IgG decreased to 1,000 mg/dl (T1,000) was 19.1 hours for the Arabi...
Genetic linkage in the horse. II. Distribution of male recombination estimates and the influence of age, breed and sex on recombination frequency. In the present study an extensive amount of data, comprising more than 30,000 offspring in total, was analyzed to evaluate the influence of age and sex on the recombination frequency in the K-PGD segment of the equine linkage group (LG) I and the influence of age, breed and sex on recombination in the Al-Es segment of LG II. A highly significant sex difference is reported for both segments. Male and female recombination values in the K-PGD segment were estimated at 25.8 +/- 0.8 and 33.3 +/- 2.5%, respectively. Similarly, recombination was less frequent in the male (36.6 +/- 0.7%) than in the f...
Effects of placement of intravaginal sponges on LH, FSH, estrus and ovarian activity in mares during the nonbreeding season. Eight seasonally anestrous mares were administered intravaginal polyurethane sponges on December 15 and then weekly thereafter until February 1. Control mares received no sponges or genital contact. Sponge insertion caused an immediate surge in follicle-stimulating hormone (FSH) concentrations in jugular plasma in 50% of treated mares whereas no control mares had surges in FSH (P less than .05). The effect of treatment on luteinizing hormone (LH) concentrations was much less dramatic and only three treated mares appeared to have positive responses. Sponge-treated mares exhibited positive respo...
Serological and bacteriological survey of three horse studs for contagious equine metritis. A bacteriological and serological survey for evidence of contagious equine metritis (CEM) was made during the 1980 breeding season on 3 horse studs in South Australia with a history of previous infection. Swabs from the clitoral sinus and the cervix were cultured for Haemophilus equigenitalis and serum was screened for antibody using the complement fixation test (CFT) and the enzyme-linked immunosorbent assay (ELISA). The specificity of both tests was greater than 0.99 but the ELISA was more sensitive in detecting antibody in infected mares. On the evidence presented it was concluded that H. e...
Assessment of the sexual behavior of pregnant mares. Pregnant mares (N = 12) were observed with a stallion from early gestation until parturition for sexual behavior. Observations were conducted for 20 min per day for 5 days each month from September until July. No mares exhibited full estrus and no intromissions or ejaculations occurred at any time during the study. Social interactions such as male approach and female/female mutual grooming occurred with greater mean frequency or duration in some months of spring and fall than in winter months. (P less than 0.05). None of the recorded behaviors differed by month of gestation. In a comparison of...
Continuous caudal epidural and subarachnoid anesthesia in mares: a comparative study. A new technique for producing continuous caudal epidural analgesia (CEA) and caudal subarachnoid analgesia (CSA) in adult horses (mares) without causing loss of pelvic limb function is described. A modified 17-gauge Huber-point directional needle was used to place a catheter with stylet into either the epidural or subarachnoid space at the lumbosacral intervertebral junction. The catheter was positioned at either the midsacral (S2-3) subarachnoid space or caudal portion of the sacral (S-3 to S-5) epidural space in 7 mares. The position of the catheter was confirmed radiographically. A 2% solut...
[Antiluteolytic activity of embryos in various animal species]. In mare, sheep and bitch the action of PGF2 alpha have been studied in the early pregnancy. Prostin F2 alpha (Upjohn) and Gabbrostim (Vetem ) are commercial names of PGF2 alpha used at doses which are luteolytic in the non pregnant female. Seric progesterone showed a temporaneous decrease but after four or five days the initial values were restored and none of the experimental females aborted. In the opinion of authors, embryo per se and/or with its adnexa might have interacted blocking the mechanism of luteolysis induced by the administration of PGF2 alpha.
Changes in plasma cortisol concentrations during the ovulatory cycle of the mare. Daily blood samples from four mares were assayed for cortisol through a total of eight ovulatory cycles. Mean cortisol concentrations on days -14, -13, -10, -9 and -8 before ovulation (dioestrus) were greater than on days -5 to -1 (oestrus). The highest mean (+/- S.E.M) value of cortisol occurred on day -10 (260 +/-28 nmol/l) and the lowest on day -2 (142 +/- 14 nmol/l). A single episode on a day in late dioestrus characterized the maximum cortisol value per cycle for five of eight cycles. Extraction of plasma samples with petroleum ether or chromatography before assay, to eliminate interferen...
Evidence that changes in LH pulse frequency may regulate the seasonal modulation of LH secretion in ovariectomized mares. To determine whether tonic LH secretion in ovariectomized mares is characterized by pulsatile release, frequent blood samples (every 15 min) were collected from 5 ovariectomized horse mares in nine 8-h periods between February and May. Mean serum LH concentrations increased 9-fold and were associated with a 4-fold increase in mean LH pulse frequency. These results provide the first evidence of pulsatile LH release in ovariectomized mares and suggest that the increasing daylengths of the spring months may increase serum LH by increasing LH pulse frequency.
Effects of testosterone, dihydrotestosterone and estradiol on gonadotropin release after gonadotropin releasing hormone administration in cyclic mares. Sixteen intact cyclic mares were treated on the fourth day of estrus and then every other day for a total of six injections with 1) testosterone propionate, 2) dihydrotestosterone (DHT) benzoate, 3) estradiol (E2) benzoate or 4) safflower oil. Mares were given gonadotropin releasing hormone (GnRH) on Day 3 of estrus (pretreatment) and again 24 h after the last steroid or oil injection. Treatment with testosterone propionate resulted in a greater (P less than 0.05) follicle-stimulating hormone (FSH) response to the second injection of GnRH compared with all other treatments. Treatment with DHT ...
Glutathione peroxidase activity in the blood of healthy horses given different selenium supplementation. Glutathione peroxidase (GSH-px) activity in the blood is correlated to the amount of selenium which was given to the horse. Currently recommended doses of selenium seem to be sufficient in order to prevent selenium deficiency. The blood GSH-px in foals reflects the amount of selenium given to the mare during pregnancy.
Transmission of equine cyathostomes (Strongylidae) in central Texas. After foaling, 6 mares and their foals were placed on equine parasite-free pastures. Observations of fecal nematode eggs and pasture larvae indicated peak cyathostome egg production occurred in late August and early September, with greatest numbers of larvae on the forage appearing during October. Two foals were necropsied for parasitologic evaluations at approximately 155 days of age. Both had approximately 100,000 adult cyathostomes, mostly Cylicostephanus longibursatus, Cylicocyclus nassatus and Cyathostomum catinatum. However, there were nearly 7 times more cyathostome larvae (189,004) in ...
Leptospiral infection in aborted equine foetuses. During an investigation of equine abortion, leptospiral infection was demonstrated in nine out of 22 foetuses examined by immunofluorescence and culture. Strains belonging to four serogroups (Australis, Pomona, Hebdomadis and Icterohaemorrhagiae) were isolated. The age of leptospira infected foetuses ranged from six months to term.
Follicle stimulating hormone, luteinising hormone and progesterone concentrations in the blood of thoroughbred mares exhibiting single and twin ovulations. The concentrations of follicle stimulating hormone, luteinising hormone and progesterone were measured in serial blood samples taken throughout one or more oestrous cycles from 12 Thoroughbred mares, some of which exhibited single and others twin ovulations. The resulting profiles clearly demonstrated that no simple relationship exists between circulating gonadotrophin levels and subsequent ovulation rate in the mare. However, plasma progesterone concentrations during dioestrus are, as expected, higher following twin than single ovulations. The findings suggest that the underlying cause of twi...
Experimental production of neonatal isoerythrolysis in the foal. Serological evidence with or without clinical signs of neonatal isoerythrolysis was experimentally produced in 6 of 8 foals born to mares allo-immunized with washed erythrocytes from the stallion. Blood group antigens were determined in all mares, stallions and foals, and the incompatible antigenic factor(s) responsible for the disease were defined. In 5 of 8 foals born to alloimmunized mares, a single antigenic factor difference accounted for the erythrocyte incompatibility between mare and foal. The erythrocyte antigen suspected as the most responsible for isoerythrolysis observed was A1. Ag...
Evaluation of a series of testing procedures to predict neonatal isoerythrolysis in the foal. A series of modified (field) tests were compared to a crossmatch between mare and foal for their reliability in predicting neonatal isoerythrolysis (NI) in eight foals born to experimentally alloimmunized mares. In the field tests, mare's serum, plasma and colostrum were combined with foal erythrocytes washed by a modified procedure to determine which combination was the best predictor of impending NI. A consistent grading system for agglutination and hemolysis was employed. The field tests using mare's plasma demonstrated less agglutination and hemolysis than tests where serum was employed. I...
Release of 3H2O from 1 beta,2 beta[3H]androstenedione by equine granulosa cells. Granulosa cells were harvested from mares at various stages of the oestrous cycle and incubated in Krebs-Ringer bicarbonate buffer with 1 beta,2 beta[3H]androstenedione as substrate. The release of 3H2O expressed as CPM/h/mg protein varied from 44000 to 768000 in follicles from 7 mares. The release of 3H2O was not significantly altered by luteinizing hormone, follicle stimulating hormone or pregnant mare's serum gonadotrophin. There was a significant negative correlation between the release of 3H2O and the concentration of progesterone in the follicular fluid. Based on the assumption that the ...
