Mare Age Research Articles

Epidemiology and reproductive outcomes of EHV‐1 abortion epizootics in unvaccinated Thoroughbred mares in South Africa

Equine herpesvirus 1 (EHV-1) is one of the most common causes of infectious abortion in mares. Analysing the demography of outbreaks and detailing subsequent reproductive performance of affected mares will assist in the management of future (threatened) epizootics. To examine the epidemiology and reproductive outcomes of 2 EHV-1 abortion epizootics with very different patterns of morbidity. Epidemiological and reproductive data were analysed retrospectively following abortion epizootics associated with EHV-1, but initiated via different routes, among unvaccinated mares on 2 Thoroughbred farms in South Africa. Aborting mares were assigned to either the EHV-1 abortion cohort via positive immunostaining (Farms 1 and 2) or quantitative PCR (Farm 2) on tissue samples, or to the non-EHV abortion cohort. During their respective epizootics, EHV-1 abortions affected 9/30 (30.0%) and 18/316 (5.7%) of the pregnant mares on Farms 1 and 2, respectively; there were also 25 (7.9%) non-EHV abortions on Farm 2. Epizootic differences included: durations (Farm 1 = 135 days; Farm 2 = 34 days), intervals between first and subsequent abortions (Farm 1 = 39 days; Farm 2 = 2 days) and intervals to confirmation of EHV-1 (Farm 1 = 40 days; Farm 2 = 2 days). The median (range) age of EHV-1 abortion mares (8.0; 5-18 years) in both epizootics was similar but significantly younger (P = 0.004) than the 25 non-EHV-1 abortion mares (11.0; 4-24 years) on Farm 2. Gestation stage (median; range) of EHV-1 (291.5; 277-313) and non-EHV-1 (211.9; 61-339 days) abortions were significantly different (P = 0.001). The post abortion complications and subsequent reproductive outcomes had no significant association with EHV-1 abortion. The marked difference in morbidity between the 2 epizootics may be associated with routes of introduction or intervention strategy dictated by availability of molecular diagnostic techniques. Unexpectedly, EHV-1 was not more commonly associated with post abortion complications.

Exposure to stallion accelerates the onset of mares' cyclicity

Horses (Equus caballus) belong to the group of seasonally polyestrous mammals. Estrous cycles typically start with increasing daylight length after winter, but mares can differ greatly in the timing of onset of regular estrus cycles. Here, we test whether spatial proximity to a stallion also plays a role. Twenty-two anestrous mares were either exposed to one of two stallions (without direct physical contact) or not exposed (controls) under experimental conditions during two consecutive springs (February to April). Ovarian activity was monitored via transrectal ultrasound and stallion's direct contact time with each mare was determined three times per week for one hour each. We found that mares exposed to a stallion ovulated earlier and more often during the observational period than mares that were not exposed to stallions. Neither stallion identity nor direct contact time, mare age, body condition, size of her largest follicle at the onset of the experiment, or parasite burden significantly affected the onset of cyclicity. In conclusion, the timing of estrous cycles and cycle frequency, i.e., crucial aspects of female reproductive strategy, strongly depend on how the mares perceive their social environment. Exposing mares to the proximity of a stallion can therefore be an alternative to, for example, light programs or elaborated hormonal therapies to start the breeding season earlier and increase the number of estrous cycles in horses.

Effects of exogenous ghrelin infusion on feed intake and metabolic parameters of energy homeostasis in Standardbred mares

Six Standardbred mares (age 12±2 years, body weight 502±63 kg; mean ± standard deviation) were given 1.6 µg/kg acylated human ghrelin or vehicle treatment as an intravenous bolus in a randomised, cross-over design to test the hypothesis that exogenous ghrelin infusion would increase feed intake and alter metabolic parameters of energy homeostasis, leptin, glucose, insulin and cortisol. After the horses had initial access to hay cubes for 1.5 h, doses were given and hay cubes were available once again. Leftover feed was weighed 6 times over each of the 24 h testing periods. Blood samples for measurement of active ghrelin, growth hormone, leptin, glucose, insulin and cortisol were taken at time 0 (immediately before infusion) and 20, 40, 60, 80, 100, 120, 240, 480, and 720 min post-infusion. Every 10 min, the horses’ behaviour was recorded for eating, drinking, resting, and other behaviours. Ghrelin infusion did not increase (P≯0.05) feed intake in the mares as a group, but did increase feed intake (P<0.04) in horses that had the highest growth hormone response to ghrelin infusion. Plasma concentrations of active ghrelin growth hormone, glucose, insulin and cortisol were all increased (P<0.05) by ghrelin infusion. There was no significant change in plasma leptin concentration due to treatment. Ghrelin infusion did not cause a significant change in the number of eating episodes either 2 h post-treatment or for the 24 h testing period. Regression analysis suggests that the increase in feed intake in horses with the highest growth hormone response to ghrelin infusion may be due to their lower (P<0.05) body condition score and % body fat compared with horses that did not increase feed intake and had lower growth hormone response to ghrelin infusion.

Factors Affecting the Incidence of Postpartum Fever in Heavy Draft Mares

Postpartum metritis is a common problem in many animal species. In equine medicine, sequelae of postpartum metritis vary from delay in uterine involution to development of systemic acute metritis (SAM), toxemia, and laminitis. Heavy draft mares potentially have higher risk of suffering from SAM than light breed mares. Postpartum fever (PF) mostly appears as a sign of SAM. The purpose of this study is to analyze the factors affecting the incidence of PF in 158 foalings from 62 heavy draft mares by multiple logistic regressions. The objective variable was the incidence of PF, and the explanatory variables were year foaled, month foaled, age of mare, breed of mare (crossbred heavy draft horse vs. Percheron), gestation length, foaling difficulty (easy delivery vs. dystocia), retained fetal membranes, stillbirth, and sex of offspring. Twenty-four out of 158 mares were diagnosed with PF. Stepwise regression analysis showed that breed of dams and foaling difficulty were significant risk factors for PF. Percheron mares had higher risk than crossbred mares (odds ratio: 3.4). Dystocia had higher risk than easy delivery (odds ratio: 3.3). Percheron mares had higher incidence of PF than crossbred mares even in the cases of easy delivery. Risks for damage and contamination of birth canal will be increased especially if the fetal delivery needs assistance. The results of this study suggest that it is necessary to consider the foaling difficulty and the breed of dams for earlier detection of PF in peripartum heavy draft mares.

The interrelationship between antral follicle count, anti-Müllerian hormone concentration, and age in mares

Anti-Mullerian hormone (AMH) is a glycoprotein expressed by granulosa cells of small follicles in the equine ovary, and serum AMH concentrations are related to follicular reserve in a number of species. The objectives of this study were to determine: (i) the relationship between serum AMH concentration, antral follicle count (AFC), and age in mares (ii) the association between serum AMH concentration and the number of follicles classified by size (iii) the repeatability of serum AMH concentrations and AFC across estrous cycles as well as (iv) the relationship between AFC and progesterone concentrations. Mares, classified as young (3-8 y, n1⁄410), middle aged (9-18 y, n1⁄416), or old (>18 y, n1⁄419), were examined with transrectal ultrasonography during 3 interovulatory intervals. On day 12 (day 01⁄4 ovulation) of the first, day 6 and 12 of the second, and day 6 of the third estrous cycle, all antral follicles were measured and the number of follicles were classified by size ( 35 mm). Serum AMH and progesterone concentrations were determined by ELISA. A mixed model with mare as a random effect was used in the statistical analysis, and correlations between variables were determined with Spearman’s rank correlation. Antral follicle count was positively associated (P1⁄40.0003) with serum AMH concentration, and the correlation between AFC and AMH concentrations differed by age group with a higher positive correlation in older

Establishing normal foaling characteristics in Standardbred mares in New Zealand

s / Journal of Equine Veterinary Science 34 (2014) 218 218 parity of the mare; with increasing parity, foaling date became later each season. Fig. 2. The number of mares foaling during different weeks of the year and the associated daylength. The majority of foalings (78.9%) occurred between 2100 and 0800 hours (Figure 3). There was no effect of time of day of foaling on any parameter. Fig. 3. Number of mares foaling during each hour of the day. The duration of foaling (from mare down and straining or membranes visible) was less than 20 min for 90% of mares. The longer the duration of foaling, the longer it took for both the mare (p<0.009) and foal (p<0.001) to stand and for the foal to suckle (p<0.003). Duration of foaling was longer (p<0.001) in mares that were considered to be agitated (multiple attempts to rise and lie down during parturition aggression towards stud staff). Mare age and parity had no effect on duration of foaling. Most mares (89.7%) stood within 15 min of foaling; 6.8% of these mares foaled standing. Following parturition, 71.9% of foals stood within 60 min with 86.1% by 90 min, and 62.9% of foals suckled within 120 min. RFM were observed in 42% of mares; the incidence was similarly high across all 4 seasons studied (52.6%, 44.6%, 37.7% and 38.6% retained). The incidence of RFM was higher when the duration of foaling was longer (mean SEM duration retained 17.0 0.6 min, not retained 14.7 0.5 min; p<0.003), higher when mares stood more quickly after foaling (mean time to stand retained 8.0 0.5 min, not retained 9.6 0.4 min; p<0.006), higher with increased time until foal’s first suckle (mean time retained 135 6.8 min, not retained 116 5.5 min; p<0.035), higher with increasing mare age (mean age retained 11.3 0.2 years, not retained 10.6 0.2 years; p<0.021), higher when mares foaled later in the season (on average mares with RFM foaled 8.5 days later than mares that did not retain (not retained 106.9 1.2 days, retained 115.4 1.5 days; p<0.001). Incidence of RFM in mares wintered off the stud farm was 42.9% and on the stud farm was 41.6%. Mares with 3 or 4 seasons of data showed there was an effect of individual mare on gestation length (p<0.001), foaling date (p<0.001), time of foaling (p<0.026) and RFM (p<0.001) so that these characteristics were more likely to be repeated from season to season. There was no effect of mare on any other foaling parameter or attitude.

181 CYTOSKELETAL AND CHROMOSOMAL ORGANIZATION IN DEVELOPMENTALLY ARRESTED EQUINE ZYGOTES AFTER INTRACYTOPLASMIC SPERM INJECTION

Intracytoplasmic sperm injection (ICSI) has been developed as a clinical procedure in the equine industry. Not all sperm-injected oocytes develop into embryos; however, the causes of developmental failure after equine ICSI have not been studied. Our objective was to use confocal microscopy to evaluate sperm-injected equine oocytes from young and old mares that did not cleave in a clinical ICSI program, to study the hypothesis that cleavage failure is associated with cytoskeletal and chromosomal alterations and affected by mare age. Oocytes were collected from the dominant follicles of young (Y; 5–15 years old) and old (O; 20–24 years old) oestrous mares approximately 24 h after administration of deslorelin and hCG. At approximately 44 h after deslorelin and hCG administration, oocytes were injected using frozen-thawed sperm from various stallions. Injected oocytes (n = 15) that failed to cleave by 24 to 48 h were fixed in microtubule stabilization buffer extraction fixative (MTSB-XF) and stained for DNA, α/β tubulin, acetylated α-tubulin, and f-actin. Confocal z-stacks were obtained using a Zeiss LSM 5 microscope (Carl Zeiss Microscopy LLC, Thornwood, NY), and images were assessed for cytoskeletal structures and chromosome organisation using the Zeiss LSM image browser. Potential zygotes (Y: n = 6 and O: n = 9) were categorized for (1) 2 sets of chromosomes, (2) misaligned chromosomes, (3) oversized spindles (approximately twice the size of an MII spindle), and (4) actin bubbling. The number of zygotes in each category for Y and O mares were compared by Fisher's exact test. Some samples were included in more than 1 morphological category. Two separate sets of chromosomes were observed in 1 of 6 and 4 of 9 injected oocytes from Y and O mares, respectively (P = 0.58), with development stopping before fusion of male and female pronuclei. Misaligned chromosomes were present in 2 of 6 and 7 of 9 oocytes from Y and O mares, respectively (P = 0.14). Oversized spindles were observed in more Y than O potential zygotes (5 of 6 and 2 of 9, respectively, P = 0.04), representing fusion of male and female pronuclei before developmental arrest. Multiasters were associated with the oversized spindles in potential zygotes from Y (2 of 6) and O (2 of 9) mares (P = 1), with microtubule activity potentially associated with the first mitotic division. Structures associated with actin bubbling tended (P = 0.12) to be higher in uncleaved zygotes from Y than O mares (5 of 6 and 3 of 9, respectively). Of the 15 injected oocytes, 10 arrested after fusion of male and female pronuclei. We have previously observed a high incidence of chromosomal misalignment in metaphase II oocytes from old mares. In the small number of potential zygotes that were studied, chromosomal misalignment tended (P = 0.14) to be higher for old mares. Other observations, such as oversized spindles and actin bubbling, appeared to be more prevalent in the potential zygotes of Y than O mares; these observations could be associated with normal development or post-ovulatory aging of the oocyte. Additional work will focus on the roles of actin and microtubules in remodelling the cytoplasm and organizing the chromosomes after fertilization in the horse and on the role of maternal aging in fertilization failure.

Factors affecting live foal rates ofThoroughbred mares that undergo manual twin elimination

Mares diagnosed with twin vesicles at 13-17 days after ovulation commonly have one of 2 vesicles manually reduced. It is not known whether vesicle location (adjacent vs. nonadjacent), mare age, mare reproductive status, parity, month of breeding or mare plasma progesterone concentration affects live foal rates. To determine factors associated with a positive outcome (live foal) in mares undergoing manual twin reduction between 13 and 17 days post ovulation when performed by a single operator. Retrospective case-control study. Breeding records and the Jockey Club records of registered Thoroughbreds were used to evaluate factors affecting the outcome of pregnancies in mares undergoing twin elimination and mares with singleton pregnancies. Thoroughbred mares with twin pregnancies (n = 129) were matched by age, parity, farm location and month bred with mares diagnosed with a singleton pregnancy (n = 127). The effects of location of embryonic vesicles, mare age, reproductive status, parity, month of breeding, vesicle size and plasma progesterone concentration at pregnancy diagnosis on live foal rate were examined. Position of embryonic vesicles at time of manual elimination, parity and month bred had no effect on live foal rate. Live foal rates in mares >9 years of age were lower (71.8%) than in all mares ≤9 years (87.1%; P<0.05). Mares >9 years of age that had a twin reduced lost more pregnancies (34.8%) than age-matched control mares (20.0%; P<0.005). Mean plasma progesterone concentration of twin-reduced mares was greater than in control mares when compared on the same day post ovulation. Plasma progesterone concentrations did not differ between mares that lost their pregnancy and those that delivered a live foal. Mare age of >9 years is associated with decreased pregnancy rate after twin reduction. Furthering the understanding of factors that affect live foal outcome following manual twin elimination in mares.

Factors Affecting Gestation Length in Heavy Draft Mares

The purpose of this study was to examine the factors affecting gestation length in 209 foalings from 65 heavy draft horses by multiple linear regression analysis. The objective variable was gestation length, and the explanatory variables were stud farm, year foaled, month foaled, age of mare, parity of mare, last gestation length, foal gender, and some meteorological parameters (the mean values of prepartum 10 days: maximum temperature, minimum temperature, average barometric pressure, and hours of sunshine in a day). The mean gestation length for 209 foalings was 334.9 (standard deviation = 8.3) days, with a range of 313-352 days. Stepwise regression analysis showed that last gestation length and foal gender had significant (P < .01) effects on gestation length. Multiple regression analysis showed that last gestation length (standard partial regression coefficient = 0.54) was more influential on the present gestation length than foal gender (standard partial regression coefficient = 0.22). The present gestation length and the last gestation length were moderately positively correlated (r = 0.56, P < .01). Colt foal (n = 106) pregnancies were significantly (P < .01) longer than fillies (n = 103) (mean ± SEM: colt 337.1 ± 0.7 vs. filly 332.7 ± 0.9). According to our results, last gestation length (mare itself) and foal gender were the main factors affecting gestation length in heavy draft horses. Once several gestation lengths are known, predictions with acceptable accuracy can be made about the gestation length of that mare's following foaling.

B‐mode and Doppler ultrasonography in pony mares with experimentally induced ascending placentitis

Early, accurate diagnosis of ascending placentitis in mares remains a key challenge for successful treatment of the disease. Doppler ultrasonography has shown promise as a tool to diagnose pregnancy abnormalities and is becoming more available to equine clinicians. However, to date, no studies have prospectively compared this technique to standard B-mode measurement of the combined thickness of the uterus and placenta (CTUP). The objective of the current study was to compare Doppler and B-mode ultrasonography for the detection of experimentally-induced ascending placentitis in mares. Eleven healthy pony mares in late gestation were used in this study. Placentitis was induced in 6 mares between Days 280 and 295, while 5 mares served as negative controls. All mares were intensively monitored until delivery. Fetal heart rate, CTUP, uterine artery blood flow (resistance index, pulsatility index, arterial diameter and total arterial blood flow) and physical examination findings were recorded at each examination. Mares with an increased CTUP above published values were treated in accordance with published recommendations. Foals and fetal membranes were examined at birth. Ultrasonographic parameters were compared between groups using ANOVA. Foal viability and histological presence of placentitis were compared using a Fisher's exact test. The CTUP was increased above normal in 5 of 6 inoculated mares within 3 days after inoculation (P = 0.05). The sixth inoculated mare was excluded from subsequent data analysis. Uterine artery blood flow, physical examination findings and fetal heart rate were not different between groups. Gradual increases in CTUP, arterial diameter and total arterial blood flow were detected with increasing gestational age in the control mares (P = 0.02, P = 0.00001 and P = 0.00001, respectively). The CTUP, but not uterine blood flow, was different between groups (P = 0.00001). Recorded CTUP values for control pony mares were similar to previously published values for light breed horses.

Determining the Gestational Age of Crioulo Mares Based on a Fetal Ocular Measure

The practice of covering in herds is often used in Crioulo breeding farms, thus not allowing the determination of ovulation dates and the early detection of pregnancies. This fact complicates the estimation of gestational age after 70 days of conception. This study aimed to evaluate the diameter of the fetal orbits of Crioulo mares to develop a formula to estimate a gestational date. Measurements of 164 fetal ocular orbits were performed in 124 Crioulo mares with gestational ages ranging between 119 and 341 days. The current study observed a linear growth pattern of Crioulo fetal orbits up to 341 days of gestation. Thus, obtaining a suitable linear regression model to determine the gestational age of Crioulo mares based on fetal ocular orbit diameter measure is possible. The obtained model was y = 8.3756x + 11.90, where y represents the gestational age in days, and x represents the diameter of the fetal ocular orbit in millimeters. This formula had an r2 of 0.985 (P < .001). We conclude that this model allows researchers and veterinarians to accurately estimate the gestational age of Crioulo mares between 4 and 11 months of pregnancy.

Factors influencing foaling rate following colic surgery in pregnantThoroughbred mares inCentralKentucky

Clinical experience has suggested that foaling rates following colic surgery in the pregnant mare are influenced by days of gestation. This premise has not been supported in previous studies. We also aimed to determine the effects of other potential influencing factors. To determine the influence of age of gestation on foaling rates in pregnant mares following colic surgery and evaluate the relationships between other factors and foaling rates. Medical records of Thoroughbred mares, which had colic surgery performed from 1993 to 2007 at the Rood and Riddle Equine Hospital, were reviewed. Mares identified in the record as pregnant or bred within the previous 15 days were included in this study. Age of the mare, date of surgery, gestational age, duration of colic at admission, packed cell volume at admission, surgical diagnosis, duration of general anaesthesia, intraoperative hypotension, intraoperative hypoxaemia and post operative signs of endotoxaemia were recorded. A mare was considered to have a live foal if that foal was registered with the North American Jockey Club. Of the 228 mares, where pregnancy had been confirmed, 152 (66.7%) had a live foal registered after surgery. Mares bred <40 days before surgery had a lower foaling rate compared with mares undergoing surgery ≥40 days after breeding: 48.7% vs. 69.8% (odds ratio [OR] = 0.41 [95% confidence interval (CI) 0.20-0.83], P = 0.012). Foaling rate was also influenced by mare's age (P = 0.008) and duration of colic signs before surgery (P = 0.03). The prognosis for a live foal after colic surgery in the pregnant Thoroughbred mare is significantly better if the mare is ≤15 years of age and ≥40 days of gestation. The results of this study are useful for clinicians offering a prognosis for a live foal following colic surgery in pregnant mares.

Reproductive performance of Thoroughbred mares in the Waikato region of New Zealand: 2. Multivariable analyses and sources of variation at the mare, stallion and stud farm level

AIM: The objective of this study was to utilise multivariable statistical methods appropriate for clustered data to identify mare-related explanatory variables that significantly affected the reproductive performance of Thoroughbred mares in the Waikato region of New Zealand. In addition, we aimed to determine the relative contribution of the mare, stallion and stud farm to reproductive performance. METHODS: A prospective cohort study was performed involving five stud farms in the Waikato region of New Zealand during three consecutive breeding seasons (2006–2008). A total of 1,482 individual mares contributed 2007 mare years and 3,402 oestrous cycles over the three breeding seasons. Reproductive performance was measured using three parameters; (a) first-cycle pregnancy rate (FCPR), (b) end-of-season pregnancy rate (SPR), and (c) the start-of-mating to conception interval. RESULTS: When controlled for the effects of serving stallion, stud farm and year of study the only significant mare-related variables included in the final models of FCPR, SPR and conception interval were the age of the mare and her reproductive status (classified as dry or foaling). Advancing mare age significantly reduced reproductive performance regardless of reproductive status and foaling mares had significantly poorer reproductive outcomes compared with dry mares when controlled for age. For each additional increase in year of age, the FCPR was reduced by a factor of 0.94 (95% CI=0.92–0.96) and the SPR was reduced by a factor of 0.91 (95% CI=0.88–0.93). Mares older than 14 years of age took longer to conceive after the start-of-mating compared with younger mares. The daily hazard of conception for mares 14 years and older was 0.64 (95% CI=0.47–0.83) times less than mares younger than 9 years of age. Determining the relative contribution of the mare, stallion and stud farm to the FCPR indicated that 95.9% of the variation was at the mare level, 4.1% was at the stallion level and 0% was at the stud farm level. For the SPR the variance components indicated that 92.5% of the variation was at the mare level, 6.7% was at the stallion level and 0.8% was at the stud farm level. CONCLUSIONS: The reproductive performance of Thoroughbred mares in the Waikato region of New Zealand is influenced by two main mare-related factors; the age of the mare and her reproductive status (dry or foaling). The majority of variation in reproductive performance was associated with mare-level factors and the contribution of the stallion and stud farm was relatively minor.

Uterine vascular degeneration is present throughout the uterine wall of multiparous mares. Colinearity between elastosis, endometrial grade, age and parity

Vascular degeneration is present in endometrial vessels of multiparous aged mares. The lesions associated with vascular degeneration consist of enlargement, duplication and splitting of the membrana elastica interna and perivascular deposits of elastin. However, there are no similar data available for deep myometrial vessels and the vascular layer. The objectives of the present study were to characterize the status of vasculature in full-thickness uterine necropsy samples and to correlate these findings to endometrial grade, age, and parity. Elastosis was present in myometrial vessels, as well as in large arteries and veins located between the circular and longitudinal myometrial layers. Vascular degeneration was associated with number of foals (P < 0.001) and endometrial grade (P < 0.05), but not with mare age (P > 0.05). Endometrial grade was associated with age (P < 0.001) and vascular grade (P < 0.05), but not with number of foals (P > 0.05). The presence of elastosis in the myometrial vessels was related to problems associated with chronic uterine infection (CUI) and delayed uterine clearance (DUC) of infertile mares. Uterine contractility was impaired in mares affected by CUI and/or DUC and could be related to a lack of myometrial blood flow. Additionally, degeneration of large vessels in the vascular layer may indicate a general compromise in uterine blood flow and fertility. The main conclusions were the presence of vascular elastosis in large deep myometrial vessels as well as in endometrial vessels, and that the factor with the strongest association with vascular degeneration was number of foals (P < 0.001), followed by endometrial grade (P < 0.05), but no association with mare age.

Effects of FSH and LH on ovarian and follicular blood flow, follicular growth and oocyte developmental competence in young and old mares

Objectives of the experiment were to determine the effects of mare age and gonadotropin treatments on dominant follicle vascularity, ovarian blood flow and dominant follicle growth and to associate follicular vascularity with oocyte developmental capacity. Growing follicles >30mm from young (4–9 years) and old (>20 years) mares were assessed for blood flow using color Doppler ultrasonography before maturation induction with recombinant equine LH (eLH) and immediately prior to oocyte collection at 20–24h after eLH. Pulsed Doppler was used to obtain resistance indices of ovarian arteries ipsilateral to preovulatory follicles. For eFSH-treated estrous cycles, eFSH administration was started after detection of a cohort of follicles ≥20 to <25mm and continued until a follicle >30mm. Oocytes were harvested using transvaginal, ultrasonic-guided aspirations and cultured and injected with sperm at 40±1h after eLH. Presumptive zygotes were incubated, and rates of cleavage (≥2 cells) and blastocyst formation were obtained. Embryos were transferred nonsurgically into recipients’ uteri, and pregnancy rates were assessed. Vascularity (number of color pixels per total pixels) was higher (P=0.003) in the follicles of old compared to young mares, with no significant interaction of eFSH or eLH. Effects of eFSH and time from eLH on follicle vascularity were not significant. The vascularity of follicles associated with oocytes that did compared to those that did not form blastocysts was greater (P=0.048), although follicular vascularity was less (P=0.02) for follicles associated with oocytes that did compared to those that did not develop into pregnancies. Resistance indices were not different for age, eFSH treatment, time after eLH administration and oocyte developmental potential. Growth of the dominant follicle was not associated with vascularity, although advanced age tended (P=0.09) to have a negative effect on follicle growth.

Cumulus cell and oocyte mRNA expression of hormone and growth factor receptors in mares

determined in old mares, but could represent a cause of age-associated early embryo loss. We hypothesized that alterations in the meiotic spindle and chromosomal alignment occur more frequently in the oocyte of old versus young mares. Oocytes were collected from the dominant follicles of young (4-11 yr, n 1⁄4 7) and old ( 20 yr, n 1⁄4 8) estrous mares and fixed at 44 h after administration of a GnRH analog to the donor. Oocytes were stained for DNA (Hoechst 33258) and microtubules (mouse anti a and b tubulin and goat anti-mouse-alexa488). Confocal images of the oocytes' meiotic spindles were analyzed to determine spindle integrity and alignment of chromosomes. Spindle conformation was considered normal when the following criteria were observed: bipolar organization, microtubules converging at both poles, and chromosomes evenly aligned at the equatorial plate. Atypical meiotic spindle morphology was observed in more oocytes from old versus youngmares (7/8 and 0/7, respectively; P< 0.05, Fisher's Exact Test), with oocytes from old mares having normal chromosomal alignment (n 1⁄4 1), nonaligned chromosomes (n 1⁄4 5), or a disarrangement of the spindle (n 1⁄4 2). Results of our study support that advanced mare age is associated alterations in morphology of the meiotic spindle and an increase in misalignment of chromosomes, which could affect embryo viability and developmental competence.

Factors Influencing the Frequency of Pregnancy Loss among Thoroughbred Mares in Hidaka, Japan

Pregnancy loss in mares is thought to be a main problem associated with reproductive efficiency. To clarify the situation of pregnancy loss in Thoroughbred mares in Japan, the occurrence of pregnancy loss before and after 35 days of gestation was investigated with 1,476 Thoroughbred mares in Hidaka, Japan, from 2007 to 2009. Pregnancy loss on days 17-35 was determined by ultrasound examination between 17 and 35 days after the last mating. Follow-up surveys were conducted between 35 days and foaling to determine pregnancy loss on day 35 until foaling in 843 of these mares. Using multiple logistic regression analysis, we assessed the influence of mare age, reproductive status, twin pregnancy reduction, body condition score (BCS), estrus type in foaling mares (foal heat or not), progesterone therapy, and endometrial cysts on pregnancy loss rates on days 17-35 and on day 35 until foaling in this population of mares. The pregnancy loss rates on days 17-35 and on day 35 until foaling were 5.8% and 8.7%, respectively. The overall pregnancy loss rate (day 17 until foaling, including parturient losses) was 14.7%. Risk factors for pregnancy loss included decrease in BCS between 17 and 35 days, <5 BCS at day 35, mating during foal heat, and endometrial cysts. In all, 14.7% of pregnancies were lost between day 17 and birth, contributing significantly to reduced reproductive efficiency in Thoroughbred mares in Japan. These observations indicate that mares should be maintained at high BCS and should be prevented from mating in foal heat to decrease the pregnancy loss rates.

Parturition, dystocia and foal survival: A retrospective study of 1047 births

An understanding of the normal events of foaling, causes of dystocia and clinical outcomes is important for equine practitioners. The goals of the present study were to: 1) evaluate factors that influence gestation length; 2) report duration of Stage II labour; 3) determine the frequency of dystocia and premature placental separation; and 4) determine the relationship between problems at foaling and foal survival. Foaling records of 1047 mare births were evaluated. The average gestation length was 342.7 days [corrected] +/- 0.4 days, with no effect of mare age or breed observed. Mares carrying male fetuses had a longer gestation (P < or = 0.001) than mares carrying female fetuses. A majority (52.8%) of mares foaled at night between 2000 h and 0200 h when the facility was quiet. Dystocia occurred in 10.1% of all births and the incidence rate was higher in Thoroughbred mares than in Quarter Horse mares. The most common cause of dystocia was abnormalities of fetal posture. A delay in foal delivery beyond 40 min of Stage II of labour was associated with a significant increase in foal mortality. In addition, an increase in foal morbidity and mortality was noted when the interval from birth to standing or birth to nursing was prolonged. Early detection and rapid appropriate intervention are critical to foal survival in an equine dystocia. Equine veterinarians should counsel horse owners that early recognition of a foaling problem and rapid, appropriate intervention are critical to the survival of a foal.

Gestation length and occurrence of daytime foaling of Standardbred mares on two stud farms in New Zealand

AIMS: To examine the gestation lengths and occurrence of daytime foaling of Standardbred mares foaling outdoors at stud farms in Southland, New Zealand (latitude 45˚S). METHODS: Data were collected prospectively at two commercial Standardbred stud farms (Farms A and B), during the 2008/9 and 2009/10 breeding seasons (October to February). For each foaling, the identity of the mare, date and time of foaling, gender of foal, time the mare passed the fetal membranes, time the foal stood, and foaling problems including dystocias, were recorded. The effect of farm, season, gender of foal, month of artificial insemination (AI) or foaling, age and parity of mare on gestation length, percentage of mares foaling during daylight hours, and percentage of foalings recorded as dystocia, were examined. RESULTS: A total of 614 foaling records were obtained from 507 mares. For 594 foalings with complete records, mean gestation length was 349 (SE 0.5) days. Mean gestation length was shorter for fillies (347.8 (SE 0.6) days) than colts (350.3 (SE 0.6) days) p = 0.021) and decreased with month of AI, from October to February (p = 0.001). The time of foaling was bimodally distributed with the primary peak around 0200 hours and a secondary smaller peak around 1300 hours. The percentage of mares foaling in daylight was lower on Farm A (69/285 (24%)) than Farm B (128/313 (41%)) (p = 0.001). Colt foals were less likely to be born during the day than fillies (OR = 0.63; (95% CI = 0.44–0.88); p = 0.008), but there was no effect of age or parity of mare or month of foaling (p>0.05). CONCLUSIONS AND CLINICAL RELEVANCE: Mean gestation length of mares in this study was longer than that previously reported from other countries. Longer gestation length decreases the time available for these mares to get back into foal in the same season. It is important that managers take this into account and ensure optimum conditions for conception; breeding at the first postpartum oestrus may be essential. There were more mares foaling in daylight hours on one stud than has previously been reported. Under these conditions mares should be monitored for foaling during daytime as well as at night.

Investigation of strongyle EPG values in horse mares relative to known age, number positive, and level of egg shedding in field studies on 26 farms in Central Kentucky (2010–2011)

A parasite study was done in 1,300 horse mares on 26 farms in Central Kentucky over a 5-month period in 2010 and 2011. The mares included 1,114 Thoroughbreds (TB) on 24 farms, 64 Standardbreds (SB) on 1 farm, and 122 mixed light horse types (MLH) on 1 farm. The objective of this research was to determine strongyle eggs per gram of feces (EPG) counts for evaluation by known age, number positive, and level of egg shedding by the mares. This was done to establish strongyle EPG profiles for the mares to aid in determining whether antiparasitic treatment was necessary. Eggs found were considered those of small strongyles. (A) For the Thoroughbred mares, (1) 362 (32%) were EPG-positive, and (2) the average (percentage) of EPG-positive mares by year of age was 3-5 (54%), 6-10 (36%), 11-15 (24%), 16-20 (17%), and >20 (21%); (3) EPG average counts were similar for all age categories except for the 6- to 10-year-olds, which were higher; (4) and the average (percentage) of positive mares by 100 units of EPG counts was ≤100 (50%), ≤200 (62%), ≤300 (70%), ≤400 (76%), ≤500 (80%), and >500 (20%). (B) For the Standardbred mares, 31 (48%) were EPG-positive; (2) the average (percentage) of EPG-positive mares by year of age (no >20 sampled) was lowest for the 3-5 and 16-20 categories and highest for the 6-10 and 11-15 groups; (3) EPG average counts by years of age were lowest for 3-5, 11-15, and 16-20 groups and highest for the 6-10 group; and (4) the average (percentage) of positive mares by 100 units of EPGs was 62% for the ≤100 category, 71-84% for ≤200 to ≤400 units, and the highest (97%) for the ≤500 unit. (C) For the mixed light horse type mares: (1) 94 (77%) were EPG-positive, (2) the average (percentage) of EPG-positive mares by age was lowest for the two oldest age groups, higher for the 11 to 15-year-old age group, and highest for the two youngest age groups; (3) EPG average counts by year of age were lowest for the 16-20 group, higher for the 6-10 and >20 groups, and highest for 3-5 and 11-15 groups; (4) the average (percentage) of positive mares by 100 units of EPG counts was lowest for the ≤100 category (23%), increasing about 10% progressively in ≤200 to ≤500 categories, but lower (37%) for the >500 category. (D) For all the three mare types (TB, SB, and MLH), 37% of the mares were EPG-positive, and 63% of the mares were EPG-negative; for the age (years) of positive mares, about one half belonged to the 3-5 category and a progressive decrease was seen for the 6-10, 11-15, and 16-20 groups, and 36% for the >20-year-olds; the mean strongyle EPGs highest range was seen in the 11- to 15-year-olds; the highest mean was in the 6- to 10-year-olds, and the lowest mean in the 3- to 5- and 16- to 20-year-olds. For the grouping of the strongyle EPG values by units of 100, three-fourths were in the ≤500 category, and the lowest percentage was for the >500 category. This research showed the value of strongyle EPG profiling for the mares. It was most useful for TBs where data from a large number of horses showed that over two-thirds were EPG-negative, indicating that there would be no known problem in deciding not to deworm them. While data were not as clear-cut on the SB and MLH mares, several of those which were negative and with "low" EPG values could be excluded from antiparasitic treatment.