A survey of early pregnancy losses in West German thoroughbred mares

Embryonic resorption is reported as the main reason for early pregnancy losses in the West German Thoroughbred mare. An analysis of breeding records for the last 11 years showed a resorption rat of 8.4 per cent. Evidence was obtained that these early embryonic losses were associated with too early conception after foaling and with the state of lactation.     

Insulin-like growth factor-I as a follicular growth promoter during early pregnancy in thoroughbred mares

To elucidate the physiological role of insulin-like growth factor-I (IGF-I) during early pregnancy in mares, number of ovarian follicles was monitored ultrasonically during different stages of the first trimester of pregnancy in 36 thoroughbred mares. From 9 of 36 mares, blood samples were collected weekly from the mating day till the end of the first trimester of pregnancy and plasma IGF-I profiles were examined with other hormones, like follicle stimulating hormone (FSH), luteinizing hormone (LH), ir-inhibin, progesterone and estradiol-17beta. Plasma IGF-I level fluctuated throughout the studied period with four peaks on the 7th, 28th, 49th and 84th days of pregnancy. Plasma IGF-I showed a positive correlation with plasma FSH (P<0.05), whereas no correlation was found with other hormones during the studied period. Plasma IGF-I had no correlation with the foetal size, but positive correlation with the number of large (> 30 mm) and medium (10-30 mm) follicles. These results suggested that IGF-I might produce from the medium and large follicles during early pregnancy and promote to develop their growth via pituitary FSH mediated effects in the mares.     

A field study of patterns of unobserved foetal loss as determined by rectal palpation in foaling, barren and maiden thoroughbred mares.

Records of 1,009 pregnancies in 574 foaling, barren and maiden Thoroughbred mares on a single stud farm, over a period of 12 years were examined. The farm is situated in the eastern Cape Province of South Africa, at an elevation of 1,800 m, and in an area of climatic extremes. Records of 604 pregnancies in 249 foaling Thoroughbred mares were examined. For these purposes, those pregnancies in which a mare conceived in the same breeding season during which she had foaled were considered as pregnancies in foaling mares. Pregnancy was confirmed by rectal palpation by a single experienced practitioner. Of the 604 pregnancies examined, conceptus attachment occurred in the horn opposite the previously gravid horn in 345 cases (57%), and in the previously gravid horn in 259 cases (43%; P less than 0.005). Unobserved foetal loss after pregnancy diagnosis amounted to 30 (9%) in the former group, while in the latter group (pregnancy established in the postgravid horn) 46 pregnancies were lost (18%; P less than 0.005). This study confirmed that conceptus attachment tends to occur in the uterine horn opposite the previously gravid horn in foaling Thoroughbred mares conceiving during the same season. A significantly higher incidence of foetal loss accompanied conceptus attachment in the postgravid horn. Of 242 pregnancies in 162 previously barren mares, 95 (39%) occurred in the left uterine horn and 147 (61%) in the right horn (P less than 0.005). The incidence of pregnancy failure in this group was 7%. The side of attachment did not affect the rate of loss. Evaluation of the records of 163 maiden mares revealed that conceptus attachment occurred in the left uterine horn in 58 (36%) pregnancies and in the right horn in 105 (64%) pregnancies (P less than 0.005), which is consistent with previously reported observations. Pregnancy failure was recorded in 4% of maiden mares. Side of attachment did not influence rate of loss in this group.     

Factors concerning early embryonic death in thoroughbred mares in South Korea

A total of 384 Thoroughbred mares were investigated to determine and evaluate the features of early embryonic death at nine equine farms on Jeju Island, South Korea, from 2001 to 2003. Overall, 771 matings for 384 mares resulted in 376 pregnancies 15 days after ovulation. Subsequently, 12.2% (46/376) of these early conceptuses were lost within 45 days after ovulation. Furthermore, about three quarters of the 46 embryonic deaths occurred between 16 and 25 days after ovulation. The incidence of embryonic death was highest in the barren (17.2%), more than 15 years old (15.4%), and more than 10 parities (18.2%) groups compared with the other groups (9.1-16.9%). Mares mated in March, April, and during the first estrus postpartum had higher embryonic death rates, (19.6%, 17.2%, and 24.6%, respectively). Mares with abnormal fluid and cysts in the uterus (18.0%) or multiple embryonic vesicles (23.1%) had higher embryonic death rates than those with normal uterine conditions (9.8%) or single embryonic vesicles (10.5%). The condition of mares, such as breeding condition and the environment of the embryo or fetus, are the major factors in relation to occurrence of early embryonic death.     

Prevalence of carpal fractures in thoroughbred and standardbred racehorses

The prevalence of carpal fractures was determined for 211 thoroughbred and 75 standardbred racehorses. Statistically significant differences were found in the location of fractures between the 2 breeds. In the thoroughbred and standardbred groups, total fractures (460) were distributed nearly equally between the left (224) and right (236) carpi. The most common site of fracture in the thoroughbred group was the distal aspect of the radiocarpal bone (112), whereas the most common site of fracture in standardbred horses was the proximal surface of the third carpal bone (61). Slab fractures were more common in the right carpus of thoroughbred horses (29 right/11 left), but were distributed equally between the left (11) and right (11) carpi of the standardbred group. Fractures of the distal border of the radius and intermediate carpal bone were more common in the left carpi of the thoroughbred group and were relatively uncommon among standardbred horses. Fractures within the intercarpal joints (313) were more common than those within the radiocarpal joints (147) in thoroughbred and standardbred horses.     

Epidemiological studies on abortions in Indian thoroughbred mares

Young mares up to 8 years of age accounted for 41.55 percent of abortions. Forty and one quarter (40.25) percent of abortions were recorded in the 8th month of gestation. Twin abortions were 25.98 per cent and correlated directly to overall abortions.     

Retrospective study on vulvar conformation in relation to endometrial cytology and fertility in thoroughbred mares

Changes in the conformation of the vulva predispose the mare to uterine infection. Vulvoplasty for closure of the upper vulvar lips improves fertility. Not all mares are resutured after parturition, but are resutured after mating. No clinical data have hitherto been published on the reproductive outcome in mares that are resutured or not after parturition. The objectives of the present study were to investigate relationships between vulvar status (not Caslick-operated, group A; previously Caslick-operated and/or not resutured after the last parturition, groups B and C respectively) and endometrial cytology, conception rate and live foal rate for different age groups and categories of Thoroughbred mares. A careful examination of the vulvar area, and endometrial sampling for bacteriology and cytology was performed. The mares were naturally mated once during oestrus (never foal heat) by one of two stallions. Mares belonging to vulvar status group A had the highest conception rate and live foal rate, whereas the lowest conception rate and live foal rate occurred in mares with vulvar status group C. A multifactorial analysis revealed that the vulvar status at arrival had a significant effect on pregnancy rate and live foal rate, but not on fetal loss. Stallion, year and age group had no significant effect on any of the three variables analysed. In conclusion, optimizing managerial factors such as resuturing Caslick-operated mares immediately after parturition to minimize growth of micro-organisms with a subsequent endometritis will contribute to their conception and that they carry a pregnancy to term.     

Uterine and fetal dynamics during early pregnancy in mares

Fetal activity and mobility and changes in diameter of the allantoic fluid compartment in the uterine horns were studied in mares between days 69 and 81 of pregnancy by use of transrectal ultrasonography (n = 12) and transcervical videoendoscopy (n = 8). The insertion tube of the videoendoscope was positioned within the allantoic sac to permit viewing of the fetus and entrance to each uterine horn. Each uterine horn was divided ultrasonographically into 3 segments of equal length, and the horns were designated on the basis of side of umbilical attachment (cord vs noncord horns). The diameter of the allantoic fluid compartment in the cornual segments increased (P less than 0.05) over the cranial (18.6 +/- 1.9 mm), middle (35.6 +/- 2.9 mm), and caudal (51.7 +/- 4.4 mm) segments, but differences between cord and noncord horns were not evident. Dynamic changes in diameter of the allantoic fluid compartment in cornual segments (ultrasonography) and at the entrance to each uterine horn (videoendoscopy) were detected (no significant difference between methods). During continuous videoendoscopic viewing (17 to 60 min/mare), extreme changes in allantoic fluid compartment diameter (76 to 100% of maximum to 0 to 25% of maximum or vice-versa) occurred an equivalent of 2.6 times/h/horn entrance; changes had an average duration of 3.4 minutes. A change from 100% (maximal diameter) to 0% (no visible lumen) or vice-versa occurred an equivalent of 1.3 times/h/horn entrance. Sometimes the uterine wall was so closely constricted++ around the fetal-amniotic unit that no intervening allantoic fluid was ultrasonographically detectable whereas at other times the uterus in the same location was widely dilated.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of a new early pregnancy test in mares

The goal of this study was to evaluate the accuracy of the early conception factor (ECF) assay test to answer the following questions: (1) Can the test be used reliably to make a decision to flush an embryo donor mare? (2) Can the test be used to detect early embryo loss before day 17 in the mare? (3) Can the test accurately diagnose non-pregnancy?The performance of the test (sensitivity, specificity, positive predictive value [PPV], and negative predictive value [NPV]) was measured against the results of embryo flushing (n = 28) in 1 group and against ultrasound pregnancy diagnosis in another group (n = 17). Serum samples were taken from embryo donor mares on day 8 post-ovulation (day of embryo flushing) and from the embryo transfer recipient mares on days 6 to 8 after embryo transfer (day of pregnancy diagnosis by ultrasound). The tests were set up and read on the same day by 3 blinded observers. The kappa (κ) value, for agreement among the 3 blinded readers of the test, was 0.64.The sensitivity, specificity, PPV, NPV, and accuracy were, respectively, 42.6%, 51.9%, 63.8%, 31.1%, and 46.8%.Under the conditions of the current study, the test proved to be unreliable for detection of the presence of an embryo.     

Pharmacokinetics of gentamicin in mares in late pregnancy and early lactation

The disposition of drugs may differ between pregnant and nonpregnant animals, necessitating a change in dosage. We hypothesized that volume of distribution or clearance may be different for aminoglycoside antibiotics in pregnant mares vs. nonpregnant lactating mares. To examine this hypothesis, we administered gentamicin sulfate to seven Thoroughbred and Quarterhorse mares on two occasions, followed by plasma drug gentamicin assay and pharmacokinetic analysis. The first dose was administered 1-4 weeks before parturition (mean weight 578 kg) and the second dose was administered in the period 1-4 weeks after parturition (mean weight 518 kg). The dose administered at each time was approximately 6.6 mg/kg, intravenously (i.v.). Plasma gentamicin concentrations were determined using fluorescence polarization immunoassay and pharmacokinetic analysis was performed using a two-compartment open model. The plasma concentration vs. time profiles and total area-under-the-curve were almost identical for mares at late gestation vs. early lactation. Mean volume of distribution at steady-state was 0.15 (+/-0.02) and 0.16 (+/-0.03) L/kg, systemic clearance was 1.06 (+/-0.17) and 1.11 (+/-0.17) mL/kg/min, and mean (harmonic) elimination half-life was 2.2 and 2.1 h, for pregnant and nonpregnant mares, respectively. We concluded that there were no differences in drug distribution and clearance between pregnant and nonpregnant lactating mares. Gentamicin was also assayed in plasma of newborn foals after an injection of 6.6 mg/kg to three of the mares within 60 min of parturition. Gentamicin was undetectable in plasma samples from these foals and, therefore, apparently does not cross the placenta of mares at term.     

Chronic clenbuterol administration alters myosin heavy chain composition in standardbred mares

The purpose of this study was to examine changes in myosin heavy chain (MHC) composition due to chronic clenbuterol administration with or without exercise in mares. Unfit Standardbred mares (aged 10+/-3 years) were divided into four groups: clenbuterol (2.4 micro/kg BW twice daily) plus exercise (3 days/week for 20 min at 50% VO(2max); CLENEX; n=6), clenbuterol only (CLEN; n=6), exercise only (EX; n=5), and control (CON; n=6). Muscle biopsies were obtained from gluteus medius muscle before and after the eight-week training/administration period. MHC composition was determined via SDS gel electrophoresis and quantified using a scanning and densometric system.CLENEX and CLEN exhibited significant (P<0.05) MHC changes while EX and CON did not. MHC type IIA decreased (29.8+/-6.1 to 19.3+/-4.0%, CLENEX; and 36.8+/-12.4 to 26.4+/-7.9%, CLEN) and MHC type IIX increased (59.4+/-7.2 to 71.8+/-5.8%, CLENEX; and 50.5+/-12.5 to 62.0+/-9.3%, CLEN). Chronic clenbuterol administration with and without exercise resulted in a significant shift in MHC profile in Standardbred mares.     

Urinary excretion of pentoxifylline and its metabolites by standardbred mares.

The urinary excretion of a sustained-release formulation of pentoxifylline was studied in the horse after the oral administration of 4.0 grams of Trental tablets. Urine samples were collected for 24 hours after dosing and analyzed for pentoxifylline and its metabolites using high-performance liquid chromatography coupled with an ultraviolet detector. Six metabolites of pentoxifylline were identified in horse urine in addition to less than 0.2% of unchanged drug. Concomitant use of gas chromatography/mass spectrometry allowed for the elucidation of the chemical structures of the metabolites. Metabolism of pentoxifylline yields one demethylated derivative, four hydroxylated metabolites and a conjugate of one of the hydroxymetabolites as urine products. The demethylated derivative, 3-methyl-1-(5-oxohexyl)-xanthine, was found to be the predominant metabolite in the urine.     

Lyme disease antibodies in thoroughbred broodmares. correlation to early pregnancy failure

A serological enzyme linked immunosorbent assay (ELISA) for equine antibodies to Borrelia burgdorferi, the causative agent of Lyme disease, was utilized on three groups of Thoroughbred mares 14 days after breeding. Group A mares were located in Kentucky, Groups B and C mares were in Florida.Group A were broodmares from a breeding farm, where early embryonic losses were reported by the farm to be substantially higher than previous years. Of 78 mares a total of 19 (24%) had experienced early embryonic resorption. The early embryonic loss rate was 47% (8/17) in the seropositive group and 18% (11/61) in the seronegative group. The excessive loss rate in the Lyme positive group was statistically significant, with the Chi-square test yielding a p value of .014.Group B had 51 mares that did not conceive on the first breeding; Group C consisted of 51 mares that became pregnant on the first breeding, and maintained pregnancy for at least 60 days. Group C was age and farm matched to serve as controls to Group B. Group B showed a higher incidence (22%) of elevated concentrations of antibodies against B burgdorferi, than did Group C mares (16%).     

Metabolic response to racing and fiber properties of skeletal muscle in standardbred and thoroughbred horses

Muscle biopsies were obtained from 17 Standardbred trotters (S) and 22 Thoroughbred racehorses (T) after races which varied in length from 1200 to 2840 m. Biopsies were taken between 2 and 14 minutes from the conclusion of the race. Histochemical and biochemical analyses were performed on all muscle samples. Standardbred horses possessed fewer Type II fibers, especially Type IIB fibers, and demonstrated a higher oxidative and lower glycolytic capacity in muscle than Thoroughbred horses. Intramuscular glycogen and lac-tate concentrations were lower in Standardbred horses after racing (mean 420 and 82 mmol/kg d.w. respectively) com-pared to Thoroughbred horses (mean 545 and 148 mmol/kg d.w. respectively). Low levels of intramuscular adenosine triphosphate (ATP) (mean S 17, T 15 mmol/kg d.w.) and creatine phosphate (mean S 28, T 42 mmol/kg d.w.) were recorded in both breeds after racing. Differences in muscle enzyme activities and metabolic response to exercise between breeds were related to the different muscle fiber compositions of Standardbred and Thoroughbred horses. Within both breeds, a high percentage of Type IIB fibers was associated with a low oxidative and high glycolytic capacity in muscle and a greater lactate accumulation after racing. In Standardbred horses low intramuscular ATP concentrations post-race were associated with a high percentage of Type IIB fibers and high lactate levels. No relationship was found between placing or speed of racing and intramuscular lactate and ATP concentrations post-race. This may have been due to many other factors which affected the outcome of a race and also due to the fact that it was not known when during a race lactate accumulation and ATP depletion occurred. Since the properties of fiber types appeared to be very different, the metabolic response within individual fiber types may be more closely related to fatigue than the metabolic response measured in whole muscle.     

A field study on reproductive efficiency of mares maintained predominately on native pasture

A field study utilizing 145 mares of various age and breeding status was conducted to determine reproductive performance under native range conditions with only limited supplemental feeding. All mares had an average initial body condition score of 4.5 and a final score of 5.1 by the time breeding was completed and mares returned to pasture. Average foaling rate was 80%, and mares that had not conceived during the previous breeding season had a foaling rate of 94%, which was higher (P<.05) than 74% for lactating mares. Mares 16 years and older had a significantly lower foaling rate (P<.05) than younger mares. Old mares that were lactating at time of breeding had only a 37% foaling rate, which was less (P<.05) than for young lactating mares. The 94 mares bred by natural cover or artificial insemination that actually foaled required 1.43 cycles per conception. Lactating mares in the oldest age group required more cycles per conception (P<.05) than open mares, and these older, lactating mares also required more cycles per conception than younger mares with foals at side. Those mares diagnosed as pregnant or open at 45 days post breeding had a pregnancy rate of 97%. Average pregnancy loss for all mares was 7.7%. These data indicate that lactating mares in moderate body condition tended to skip a breeding season and that a body condition score of 5 was only marginally acceptable, especially in the case of lactating mares. Authors' address: Equine Science Program, Department of Animal Science, Texas Agricultural Extension Service, Texas A&M University, College Station, TX 77843. Technical Article Number 30023, Texas Agr. Exp. Sta.     

Concentrations of macro- and micro-elements in the milk of pasture-fed thoroughbred mares

OBJECTIVE: To determine the changes in Ca, P, Mg, Na, K, S, Cu, Fe and Zn concentrations of milk during the lactation in pasture-fed Thoroughbred mares and then calculate the dietary mineral requirements of the sucking foal and the lactating mare. PROCEDURE: Milk was sampled on days 1, 3, 7, 14, 21, 28 and at various times between 55 to 65, 85 to 95 and 135 to 150 days after parturition from 21 pasture-fed mares. The concentrations of macro- and micro-elements in the milk were determined by inductively coupled plasma emission spectrometry. RESULTS: Concentrations (mg/L) of these elements were highest in colostrum (Mg 302, Na 561, K 955, S 1035, Cu 0.76, Fe 0.79 and Zn 5.5) except for Ca (1245) and P (895), which where highest on day 7. The mean milk mineral element concentrations (mg/L) over days 55 to 150 were Ca 843, P 543, Mg 47, Na 120, K 590, S 219, Cu 0.19, Fe 0.34 and Zn 2.1. The mean plasma element concentrations (mg/L) over the same period were Ca 120, P 77.1, Mg 17.0, Na 3110, K 168, S 983, Cu 1.1, Fe 1.5 and Zn 0.49. Concentration gradients between plasma and milk were observed and, in the case of Ca, P, Mg, K and Zn, their concentrations in milk were greater than those in plasma, while a reverse situation was observed for Na, S, Cu and Fe. CONCLUSION: With the exception of Ca and P, the highest concentrations of mineral elements were observed in the colostrum. The nursing foal should have access to good pasture or creep feed, because the intakes of Ca, P and Cu from milk may be less than optimum to meet the daily mineral element requirements.     

Genotyping of isolates ofTaylorella equigenitalis from thoroughbred brood mares in Japan

Profiles of the genomic DNA of 104 strains ofT. equigenitalis isolated from brood mares with contagious equine metritis in Hokkaido during the breeding seasons from 1980 to 1993, as well as those of five strains (SS28, EQ56, EQ59, EQ70 and HH139) previously isolated in Japan were examined after restriction digestion and crossed-field gel electrophoresis. These profiles were essentially identical to each other and the various isolates and strains appeared to have a common genotype, designated genotype J, with respect to two restriction enzymes,ApaI andNotI. These results suggest a common source for all these isolates obtained over the course of more than 10 years in Japan.Abbreviations CEM contagious equine metritis - CFGE crossed-field gel electrophoresis - PFGE pulsed-field gel electrophoresis