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.     

Twinning in mares: A review of recent studies

Recent studies on twinning are reviewed. Multiple ovulations were more frequent in thoroughbreds (19%) than in quarter horses (9%) and Appaloosas (8%). The multiple ovulation rate was reduced approximately 50% in foaling mares compared to barren and maiden mares. There was a high degree of repeatability of double ovulations and twin pregnancies within mares and within family lines.Only one embryo was found in each of 23 pituitary extract-treated mares with multiple, synchronous ovulations (<2 days apart) and in each of 39 brood-farm mares with double, synchronous ovulations. Pregnancy rates (number of mares pregnant, regardless of number of embryos/mare) were significantly higher for double, synchronous ovulations than for single ovulations in artificially stimulated mares (58% vs 38%) and in brood-farm mares (83% vs 54%). The results indicated that ova produced by synchronous, double ovulations are viable and fertilizable (indicated by the higher pregnancy rates), but that one of the resulting embryos is eliminated (indicated by the absence of twins).Synchronous, double ovulations were not recorded in association with any of 107 sets of natrually occurring twins. Most (76%) of the twin sets were associated with one detected ovulation. The remaining twins were associated either with one ovulation, but a large unovulated follicle was present at the time of the last examination (10%), or with asynchronous, double estrous ovulations (14%). Twins originated more frequently (P < .05) from asynchronous, double estrous ovulations (9/57) than from synchronous, double ovulations (0/39).Approximately 50% of the mares in which twin embryos were diagnosed rectally before day 31, had 1 foal. However, mares in which twins were recorded as present at day 32–36 and day 40–42 had a single foal in only 17% and 6% of the mares, respectively. The methods used for intervention when twins were diagnosed were unsatisfactory. Complete termination of pregnancy with a prostaglandin or intrauterine flushing resulted in failure to establish a singleton pregancy during the remaining breeding season in 10/11 mares. Attempts to eliminate one embryo resulted in loss of both embryos in 6/7 mares.     

Transcervical embryo transfer in performance mares

Pregnancy was established by transcervical transfer of embryos from performance mares into recipient mares. Estrus was synchronized between donor (n = 17) and recipient (n = 43) mares. After a greater than or equal to 25-mm follicle was detected, donor mares were bred artificially daily until ovulation. Day of ovulation was recorded. Uterine flushes (n = 111) were performed on donor mares 7 days after ovulation, and recovered embryos were transferred transcervically to recipient mares within 2 hours. Embryos were recovered from 40.5% of uterine flushes. Of transferred single embryos, 65.7% resulted in pregnancy, detectable by ultrasonographic examination 23 days after transfer. Only 35.3% of twin embryos resulted in pregnancy. Results over a 4-year period were as follows: uteri were flushed on 14, 44, 31 and 22 occasions, and 8, 21, 15, and 11 embryos were recovered (1 embryo was not transferred), with 6, 11, 4, and 6 resulting in 30-day pregnancy in years 1 to 4, respectively.     

Reproductive performance of Thoroughbred mares on six commercial stud farms

The records of 1630 mare years from 6 Thoroughbred stud farms in south eastern Australia were analysed for the years 1981 to 1986. Overall pregnancy and foaling rates were 83.9% and 69.3%, respectively. When calculated per served oestrous cycle, pregnancy and foaling rates were 54.7% and 43.1%, respectively. Pregnancy and foaling rates were higher (P < 0.001) for mares 3 to 10 years of age than for older mares. There was no difference in the pregnancy rates of maiden, barren and foaling mares. The foaling rate was significantly higher (P < 0.001) in mares that became pregnant during the first served oestrous cycle (77.8%) than in mares that needed two served oestrous cycles to become pregnant (65.4%). Of all diagnosed pregnancies, 19.5% were not completed. Pregnancy loss was lower (P < 0.05) in maiden (12.4%) than in barren (19.7%) or foaling (20.9%) mares. Twins were diagnosed in 7.8% of all pregnancies. If one conceptus was lost without external interference, 84.1% of pregnancies went to term. If one conceptus was manually crushed, 55.9% of pregnancies were maintained. If prostaglandin was used to terminate twin pregnancies, 60% of mares so treated produced foals the following year.     

Novel Long-Acting Progesterone Protocols Used to Successfully Synchronize Donor and Recipient Mares With Satisfactory Pregnancy and Pregnancy Loss Rates

The present study aimed to evaluate pregnancy and pregnancy loss rates of recipients treated with alternative long-acting progesterone protocols, designed to synchronize acyclic and cyclic mares, regardless of their cycle phase. A total of 150 Campolina breed mares were used as recipients. Recipient mares were assigned to six different groups with 25 animals each. Groups 1 to 5 were treated with progesterone at some point. Group 1 (acyclic recipients); group 2 (cyclic estrous recipients with one ≥35 mm follicle); group 3 (cyclic estrous recipients with an anovulatory follicle); group 4 (early estrous cyclic recipients); group 5 (diestrous cyclic recipients), and group 6 (cyclic recipients—control). Embryos (day 8) were transferred 4 days after ovulation or 4 days after progesterone injection. Pregnant diagnosis was performed by transrectal ultrasonography 1 week after embryo transfer. Pregnant recipients were evaluated for possible losses and mares treated every 14 days with 3 g (intramuscular) of long-acting progesterone, until 120 days of pregnancy. Pregnancy at 15 days and pregnancy loss rates were recorded and statistically evaluated through multivariate regression (P < .05). Pregnancy and pregnancy loss rates were similar within groups (G1: 76%–10.5%; G2: 76%–5.9%; G3: 56%–0%; G4: 80%–10%; G5: 60.9%–0%; and G6: 60%–13.3%). In conclusion, the novel long-acting progesterone protocols proposed in this study allowed successfully the utilization of mares with asynchronous cyclic as embryo recipients, serving as an alternative specially when few recipients are available and usual synchronization is not possible.     

The influence of late pregnancy and lactation on bone metabolism in mares

Pregnancy and lactation are periods of significant influence on bone metabolism that has not been investigated in equines. To examine the influence of late pregnancy and lactation on bone metabolism in mares, the changes in the blood serum/plasma total calcium (Ca), inorganic phosphates (Pi), pyridinoline (Pyd) and 17β-estradiol (E2) concentration and the bone alkaline phosphatase (BAP) activity were investigated. The samples were taken from 11 mares on 60 ± 10 and 20 ± 10 days before foaling, and 20 ± 10 and 60 ± 10 days after foaling. The concentration/activity of Ca, Pi, Pyd and BAP increased significantly in early lactation, but the Pyd than decreased in the 4th period. A significant correlation was observed between the E2 and bone metabolism parameters. The results indicate low maintenance of normocalcaemia with reduced bone synthesis in late pregnancy and prove the role of estradiol in bone metabolism in mares during pregnancy and lactation.     

Some Factors Affecting the Rate of Pregnancy after Embryo Transfer Derived from the Brazilian Jumper Horse Breed

This study aimed to evaluate the effects of certain embryo transfer parameters on the pregnancy rate after equine embryo transfer of the Brazilian Jumper Horse breed. The size, embryonic development stage, embryo quality, and synchronization of ovulation between the donor (n = 120) and recipient (n = 420) were evaluated in 396 embryos. Embryo recovery was performed on Day 6-9 after ovulation (Day 0 = day of ovulation). The recipient mares were chosen on the day of embryo recovery, and the transfers were performed that same day. The embryo size (diameter including envelopes; n = 396) ranged from 150 to 3000 μm; 67.1% measured between 400 and 1199 μm. The embryo size (400-1199 μm vs. ≤399 μm); stage of development (n = 396; blastocyst and expanded blastocyst versus compact morula and early blastocyst); quality (n = 396; grade 1 [excellent]), 2 [good], or 3 [poor]); and synchronization of ovulation between the donor and recipient (0, 1, 2, 3, and 4 days versus −1, 5, and 6 days, respectively) all affected pregnancy rate (P < .05). The pregnancy rate did not differ significantly among transfers performed on Days 0, 1, 2, 3, and 4. In conclusion, embryos measuring 400-1199 μm produced higher pregnancy rates in recipients than embryos measuring 150-399 μm, and blastocysts and expanded blastocysts produced pregnancy more efficiently than morulae and early blastocysts. The embryo quality also affected the pregnancy rate. Synchronization of donor and recipient ovulation to Days 0-4 improved the efficiency of embryo transplant.     

Management Strategies Aiming to Improve Horse Welfare Reduce Embryonic Death Rates in Mares

The objective of this retrospective study was to evaluate the effect of management strategies aiming to improve animal well‐being on pregnancy and embryonic death (ED) rates. Breeding records of a cohort of 1206 Thoroughbred mares brought to a stallion station facility, to be bred with the stallions housed there, were evaluated during ten breeding seasons. Mares were blocked according to management strategies in two groups: Stress and Relax. Strategies used to improve animal well‐being (Relax group) were as follows: stopping the teasing routine, reducing or eliminating stall confinement, reducing the number of mares per group and maintaining herd stability during the breeding season. In barren mares, the pregnancy rate was higher in the Relax group (91.8%) when compared to the observed in Stress group (84.7%). However, no difference in pregnancy rates were observed (Stress = 85.2% vs. Relax = 86.2) in foaling mares. ED rate was higher in barren and foaling mares of the Stress group mares (25.5% and 26.8%, respectively) compared with the Relax group (16.1% and 14.7%, respectively). No significant differences were observed on foal heat pregnancy rate between groups; yet, the embryo loss on foal heat was significant reduced in Relax mares (Relax = 8.7% vs Stress = 24.5%). In conclusion, management strategies aimed to reduce social stress can reduce early pregnancy losses and the average cycles per pregnancy, improving reproductive performance in mares.     

Metabolic Profile of Broodmares During Late Pregnancy and Early Post‐Partum

Pregnancy represents a specific physiological status characterized by continuous adjustments that affect maternal metabolism of all nutrients. In the last trimester of pregnancy, mare's nutrient requirements greatly increase and most pregnancy‐associated diseases are likely to occur. Therefore, we aimed to assess the metabolic profile of broodmares focusing on the last 3 months of pregnancy and the early post‐partum. Fifteen pregnant mares (Group A) were monitored from 263 ± 3 days of pregnancy until 21 days after foaling. Seven non‐pregnant mares (Group B) were used as the control group. Blood samples were collected weekly by jugular venipuncture throughout the experimental period, and additional blood samples were collected within 24 ± 12 h of foaling. Obtained sera were analyzed for urea (Ur), creatinine (Cre), total protein (TP), total, direct and indirect bilirubin (tB, dB, iB), triglycerides (TG), total cholesterol (tChol) and β‐hydroxybutyrate (BHB). During pregnancy, Ur (p = 0.015) and dB (p = 0.028) were higher in Group A than Group B. Serum Cre, tB, iB and TG (p < 0.001) decreased after foaling; furthermore, Group A exhibited lower tChol (p < 0.001) and higher BHB (p < 0.001) than Group B during the study. There were significant interactions of time × peripartum on Ur (p = 0.007), Cre (p < 0.001), tB (p = 0.018), TG (p < 0.001) and tChol (p < 0.001). These results can be used in the interpretation of biochemical studies in late gestation mares which develop systemic disease. The improved understanding of the metabolic profile during the peripartum might assist in monitoring the health status of the broodmares to promote foetal growth and well‐being.     

Relationship between the Placental Retention Time and the Reproductive Performance at the Foal Heat in Thoroughbred and a Comparison with Heavy Draft

The aim of this study was to clarify the relationship between the placental retention time (PRT) and the reproductive performance following mating at the foal heat in Thoroughbreds. For this purpose, we interviewed 292 farmers over a period of 3 years with questionnaires evaluating foaling, expulsion of placenta and reproductive performance at the foal heat in 1,432 mares. The obtained data were later compared with a previous study of heavy draft mares. The average of the PRT of the 1,432 Thoroughbred mares was 58 ± 88 min (mean ± SD). The mean PRT of Thoroughbreds was significantly shorter than that of the148 min of heavy draft mares. The incidences of retained placenta (RP) occurring in the Thoroughbred mares were 5.2 and 4.0%, for over 3 and 4 hr after foaling, respectively. The incidence of RP over 4 hr was significantly lower than that of 25% in heavy draft mares. The pregnancy rate at foal heat of the mares in which PRT was less than 3 hr was 37%, and it significantly decreased to 11% for those with PRT of more than 3 hr. In the comparison of the reproductive performance between Thoroughbred and heavy draft mares, the pregnancy rate of Thoroughbreds dropped drastically to 10% when PRT exceeded 40, and in consequence, the pregnancy rate of Thoroughbreds was significantly lower than the 30% of heavy draft mares, which had a PRT of over 4 hr. In conclusion, the Thoroughbred mares had a low incidence of RP, however, a PRT exceeding 3 hr severely affected the reproductive performance at the foal heat.     

Effects of dietary L‐arginine supplementation to early pregnant mares on conceptus diameter—Preliminary findings

The importance of the amino acid L‐arginine (ARG) for conceptus growth and litter size has been demonstrated in various species. L‐arginine is part of embryo‐derived polyamines, a substrate for nitric oxide synthase and stimulates protein synthesis by the embryo. In the present study, we have investigated whether dietary L‐arginine supplementation stimulates early conceptus growth in mares. Warmblood mares with singleton pregnancies received either an arginine‐supplemented diet (approximately 0.0125% of body weight, n = 12) or a control diet (n = 11) from days 15 to 45 after ovulation. Diameter of the embryonic vesicle (days 14, 17, 20 of pregnancy) and size of the embryo respective foetus (length and maximal diameter, days 25–45 of pregnancy at 5‐day intervals) were determined by transrectal ultrasound. At foaling, weight and size of the foal and the placenta were determined. Blood for determination of equine chorionic gonadotrophin (eCG) and progestin concentrations was collected repeatedly. Neither eCG nor progestin concentration in plasma of mares differed between groups at any time. No effects of arginine treatment on diameter of the embryonic vesicle between days 14 and 20 of pregnancy were detected. Diameter of the embryo/foetus on days 40 to 45 of pregnancy strongly tended to be enhanced by arginine supplementation (p = 0.06). Weight and size of neither the foal nor placenta at birth differed between groups. In conclusion, L‐arginine supplementation was without negative effects on early equine embryos and may support embryonic growth at the beginning of placentation.     

A Field Study of Serum,Colostrum, Milk Iodine,and Thyroid Hormone Concentrations in Postpartum Draft Mares and Foals

Iodine, thyroxine (T4) and triiodothyronine (T3) are required for normal fetal growth, maturation, and neonatal survival. There is a lack of robust information on iodine levels found in colostrum, milk, and serum of mares and foals after a healthy pregnancy. Our objective was to characterize colostrum, milk, and serum iodine levels in healthy postpartum mares and foals (n = 10) and explore relationships with thyroid hormone concentrations. Colostrum, milk, and jugular blood samples from draft breed mares and foals with an estimated average iodine daily intake of 39 mg per mare during pregnancy were obtained at Day 0 (foaling date) and/or 10 days later. Parameters studied were (1) mare basal concentrations of serum: TT3, TT4, and iodine; (2) iodine in colostrum at Day 0 and milk iodine (Day 10); and (3) foal basal: TT3, TT4, and serum iodine (Days 0 and 10). Median ± median error colostrum iodine levels (165 ± 15.1 μg/L) were higher than milk (48 ± 5.6 μg/L; P = .007) levels. Median ± median error foal serum iodine (268.5 ± 7.6 μg/L), TT4 (1,225 ± 47.8 nmol/L), and TT3 (14.2 ± 1.1 nmol/L) at foaling date were higher than at 10 days (serum iodine: 70 ± 3.6 μg/L; TT4: 69.6. ± 20.4 nmol/L; and TT3: 5.4 ± 0.3 nmol/L). In conclusion, equine mammary tissue concentrates iodine beyond plasma levels, making colostrum and milk a significant source of iodine. Foal serum iodine levels are high in the neonatal period and are positively correlated with TT4, which is important for neonatal adaptation.     

Assessing the fertility of two mares cloned from the same founder animal

Two cloned mares, produced from the same sample of skin fibroblasts, were bred during four breeding seasons from their second year of age, as embryo donors, in exactly the same conditions, using the same stallions for both cloned mares. The aim of this study was to test the embryo donor potential of cloned mares and to compare the results obtained from two cloned mares of the same mare with other embryo donor mares (n = 31–39 per breeding season) at the same stud. For both cloned mares, 19 embryos were recovered by 43 collection attempts (44%) (7/22 for one; 12/21 for the other), 16 (84%) pregnancies (5/7 for one, 11/12 for the other) were obtained at day 14 post-ovulation (D₁₄), and 12 (3/7 for one; 9/12 for the other) foals were born. One cloned mare was a less efficient donor mare than the other (p < .05), In control donor mares, 623 embryo collections were performed, with a recovery rate (80%—496/623) significantly higher than for cloned mares. The recovery rate in the subpopulation of 2–5-year-old control donor mares (same age of cloned mares) (89%—127/143) and The recovery rate in the subpopulation of 12 control mares bred with the seven same stallions as clones (55%—17/31), were both higher than for cloned mare (p < .05). The success rate of transfer was not different between embryos produced by cloned mares (84%—16/19) and those produced by control donor mares (79%—392/496). However, the foaling rate per embryo collection was significantly lower for cloned mares (28%—12/43) than for control donor mares (52% - 325/623) (p < .05).     

Retrospective study on the incidence of postinsemination uterine fluid in mares inseminated with frozen/thawed semen

Uterine fluid accumulation has been reported after insemination or natural breeding of mares. This retrospective study examined the factors affecting the incidence of uterine fluid after insemination of frozen semen. Specifically, this study determined the association between mare age, reproductive status, fluid accumulation, and pregnancy rates in mares. Records were available from 283 warmblood mares throughout 496 cycles. Mares were divided into maiden, foaling, and barren and age groups of 3 to 9, 10 to 16, and more than 16 years. Mares were inseminated only once with frozen semen within 4 to 8 hours before or after ovulation. Ultrasound examinations were performed 12 to 18 hours after insemination. A depth of at least 20 mm of fluid was considered significant. Mares with less than 20 mm were treated with oxytocin, and those with more than 20mm of fluid were given oxytocin and uterine lavage. Pregnancy determination was performed at 14 to 16 and 30 to 50 days after ovulation. Fluid level of more than 20 mm was recorded in 25% of the cycles. Barren mares and aged mares (10-16 and > 16 years) had a higher incidence of uterine fluid accumulations. Per-cycle pregnancy rate was lower (45%) in mares with uterine fluid than in mares without uterine fluid (51%). This difference was primarily due to the reduction in fertility of mares who were older than 16 years and retained fluid after insemination. Apparently, oxytocin and lavage treatments provided acceptable fertility in the other groups of mares that had uterine fluid.

Introduction

Use of equine frozen semen is accepted by the majority of horse registries. According to several field studies,[1, 2, 3, 4 and 5] insemination of frozen semen has resulted in acceptable pregnancy rates. Postbreeding fluid accumulation is a physiologic inflammation that clears the uterus of foreign material such as excess spermatozoa, seminal plasma, bacteria, and extenders. [6, 7, 8, 9 and 10] Uterine fluid can be easily diagnosed with ultrasonography. [10, 11 and 12] Persistent postbreeding uterine fluid has been associated with a decrease in fertility after natural mating or artificial insemination (AI) of fresh semen. [11, 12 and 13] Predisposing factors to persistent fluid accumulations are reduced myometrial contractions, poor lymphatic drainage, large overstretched uterus, and cervical incompetence. [7, 14 and 15] Normal mares are able to expel uterine fluid quickly after inseminations, whereas susceptible mares accumulate fluid in their uterine lumen for more than 12 hours after breeding or insemination. [10]It is commonly stated that insemination with frozen semen leads to greater post-AI fluid accumulation than insemination with fresh or cooled semen or after natural mating. Apparently, there is only 1 controlled study on this comparison.[7] The authors reported that infusion of frozen semen resulted in a greater inflammatory response than natural breeding. In a field study, [16] 16% of mares naturally mated had persistent postbreeding fluid accumulations compared with a 30% rate reported for mares inseminated with frozen semen. [1 and 2] More recently, Watson et al. [17] reported a postbreeding fluid accumulation rate of 16%, which is identical to that reported for natural mating. [16] It is difficult to compare studies because details of mare selection and insemination or breeding frequencies are not always reported. Obviously, a higher proportion of barren and aged mares in a study would increase the incidence of postbreeding fluid accumulation. [1 and 2]The study presented herein was a retrospective study designed to determine the incidence of postbreeding fluid accumulation in a large number of mares inseminated with frozen semen. Associations were determined between mare age, reproductive status and fluid accumulation, and pregnancy rate in mares with and without uterine fluid accumulation.

Materials and methods

Mares

Records were available from 283 warmblood mares inseminated with frozen semen at the Cristella Veterinary Clinic in Italy during 1998 to 2001. Mares ranging in age from 3 to 20 years were inseminated with semen that was frozen in 10 centers and was from 34 stallions. The broodmare population was subdivided into 3 reproductive groups: 89 maiden mares (mean age, 7.2 years), 106 foaling mares (mean age, 9.4 years), and 87 barren mares (mean age, 11.9 years). Maiden mares older than 7 years were selected with biopsy scores of 1 or 2 only. Barren mares were open for no more than 2 consecutive seasons and had negative cytology and bacteriology scores. Age groups were divided as follows: 3 to 9 years (n = 132), 10 to 16 years (n = 137) and older than 16 years (n = 14). Data from 496 cycles were used. Distribution of the estrous cycles was 172, 157, and 167 in the maiden, foaling, and barren groups, respectively; and 224, 244, and 28 in the youngest, intermediate, and oldest groups, respectively.

Mare reproductive management and artificial insemination protocol

During estrus, all mares underwent a daily ultrasound examination with a 5-mHz transrectal probe (SA 600 Vet; Medison Inc., Seoul, South Korea) until 1 or more 35-mm ovarian follicles were detected. Ovulation was then induced by the intravenous administration of 2000 IU of human chorionic gonadotropin (hCG). Ultrasound examination was performed 12 hours after hCG treatment and then every 4 to 8 hours until ovulation occurred. Mares were inseminated only once within a period of 4 to 8 hours before or after ovulation. The semen used was thawed according to the distribution center's instructions and had the following minimum post-thaw quality requirements: not less than 200 × 10⁶ progressively motile spermatozoa per dose and a minimum of 30% progressive spermatozoal motility. Foaling mares were not inseminated at their first postpartum (“foal heat”) estrous period, because pregnancy rates are recognized to be lower than during the subsequent estrous periods.[18] During the first postpartum estrus, ovarian ultrasound scan examinations were performed every 2 to 3 days until an ovulation was detected. A prostaglandin F₂α injection was given 5 days later to short-cycle the mare.

Postinsemination monitoring

An ultrasound examination of the reproductive tract was performed 12 to 18 hours after insemination to detect any intrauterine fluid accumulation. The presence and depth of intrauterine fluid was recorded. Twenty millimeters or more of grade II or III intrauterine fluid[19] was recorded as a significant amount of fluid. Mares with less than 20 mm of fluid were treated with an intravenous injection of 20 IU oxytocin. For mares with more than 20 mm of fluid, oxytocin was administered, and the uterus was flushed daily with buffered saline solution: 1-L aliquots were infused and recovered until the recovered fluid was clear. In these mares, oxytocin treatment was repeated up to 3 times daily. Post insemination treatments were performed for no more than 4 days after ovulation had occurred.Pregnancy diagnosis was performed with ultrasound at 14 to 16 days after ovulation. Scans were then repeated at 30 and 50 days of gestation to confirm the presence in the uterus of an apparently healthy developing conceptus.

Statistical analysis

χ² Analysis was used to determine the effect of reproductive status and age on the incidence of fluid accumulation. In addition, the influence of persistent uterine fluid accumulation on pregnancy rates per cycle was determined for each reproductive class and age by using χ² analysis.

Results

The per-cycle pregnancy rate at 14-16 days after ovulation was 49.3% (245/496 cycles). By the end of the season, 245 of 283 mares (86.5%) were confirmed pregnant. Fluid level of at least 20 mm (grade II or III) was recorded in 126 of the 496 cycles (25.4%). Barren mares had a higher (P < .05) incidence of postbreeding fluid accumulation (64/167; 38.3%) than maiden (34/172; 19.7%) and foaling (28/157, 17.8%; Table 1) mares. The incidence of fluid accumulation was also higher in mares older than 16 years (19/28; 67.8%) than those aged 10 to 16 years (69/244; 28.2%) and 3 to 9 years (38/224; 17%). The incidence of uterine fluid was also higher (P < .05) for mares aged 10 to 16 years than those aged 3 to 9 years (Table 2). Overall, the per-cycle pregnancy rate was lower (P < .05) for mares with post-AI fluid accumulations than for those with no uterine fluid or only a small quantity of fluid (57/126, 41.9% vs 188/360, 56.2%). Pregnancy rates were similar (P > .05) for mares with or without uterine fluid when comparisons were made within maiden and barren mare groups. However, more foaling mares became pregnant when no fluid was detected after insemination. Pregnancy rate for this group (68.1%) was higher than that for maiden (44.2%) and barren (44.6%) mares (Table 3). Older mares with uterine fluid accumulations had a lower per-cycle pregnancy rate (36.8%) than mares in the same group but without fluid. Surprisingly, if no fluid was detected, the highest pregnancy rates were in mares older than 16 years ( Table 4).     

Reproductive efficiency of intensively managed Thoroughbred mares in Newmarket

The findings of a retrospective survey of 1393 Thoroughbred mares visiting 22 studfarms in the Newmarket region of the UK during the 1998 mating season were compared with those of a similar study undertaken in 1983. The effects of mare age and status, stallion, month of mating, application of uterine treatments and other parameters on the rates of singleton and twin conception and subsequent pregnancy losses were analysed. Mare age and status significantly affected the per cycle pregnancy rate and the incidence of pregnancy loss. Overall, the mean number of matings per oestrus was 1.12 and the mean number of times a mare was mated until diagnosed pregnant at 15 days after ovulation was 1.88. An overall mean per cycle pregnancy rate of 59.9% at 15 days after ovulation resulted in 94.8% of the mated mares being pregnant at least once at 15 days after ovulation. This high initial pregnancy rate fell to 89.7% by Day 35 and 87.5% by the time of the October pregnancy test; 82.7% of the mares surveyed gave birth to a live foal at term, which compares favourably with the proportion of mares foaling in 1983 (77%). However, despite improvements in the foaling rates over the last 15 years, the overall rate of pregnancy failure remains high and represents a major loss to the Thoroughbred breeding industry.     

Age-Dependent Effect of Foal Heat Breeding on Pregnancy and Embryo Mortality Rates in Thoroughbred Mares

The aim of the present study was to evaluate the correlation of age and heat cycle to determine reproductive efficiency in young and aged Thoroughbred mares bred on foal heat (FH) or on second heat (SH) after foaling. Embryo mortality (EmbM) was determined every time a mare was found open after a positive pregnancy diagnosis. Parturition to breeding interval, pregnancy rate (PregR) and EmbM rate were the dependent variables and the treatments were breeding on the FH or on SH. The cutoff age to obtain above-average probability for the EmbM was 10 years old. PregR in mares bred on FH was lower compared with SH (P < .01); however, it was neither affected by the age of mares (P > .05) nor by the age group of mares (P > .05). Regarding FH and SH, there was a difference in PregR in young mares (P < .01), unlike in aged mares (P > .05). EmbM rate was not different between mares bred on FH or SH (P > .05) although it was affected by age of mares (P < .01). EmbM was higher in oldest than young mares (P < .01). Aged mares bred on FH had a significantly higher EmbM rate compared with the young group also bred on FH (P < .01). In conclusion, the reproductive efficiency of Thoroughbred mares bred on FH is dependent of the age. Aged mares (≥10 years old) should be bred at their SH to reduce EmbM and improve reproductive performance.     

Use of a Compounded Long-Acting Progesterone Formulation for Equine Pregnancy Maintenance

The objective of this study was to test the efficacy of a compounded long-acting progesterone formulation (BioRelease P4 LA 150; BETPHARM, Lexington, KY) containing 150 mg progesterone/ml for pregnancy maintenance in mares after prostaglandin (PG) F_2α-induced luteolysis. On day 18 of gestation, mares were randomly assigned to one of four groups (n = 7/group): (1) saline-treated control (Saline); (2) PGF_2α-treated control (PGF); (3) PGF_2α- and Regu-Mate-treated (Regu-Mate); and (4) PGF_2α- and BioRelease P4 LA 150-treated (BioRelease). On day 18, Saline mares received 1 ml sterile saline IM, whereas PGF, Regu-Mate, and BioRelease mares received 250 μg cloprostenol IM. Beginning on day 18, Regu-Mate mares received 10 ml Regu-Mate orally once daily and BioRelease mares received 10 ml BioRelease P4 LA 150 containing 150 mg/ml progesterone IM once every 7 days; treatments were continued until day 45 or until pregnancy loss occurred. Pregnancy diagnosis was performed every 3 days between days 18 and 45 (or until pregnancy loss). Pregnancy loss was defined as complete absence of a discernible embryonic vesicle as determined with transrectal ultrasonography. Pregnancy loss rates between days 18 and 45 were: Saline, 1/7; PGF, 7/7; Regu-Mate, 1/7; and BioRelease, 0/7. The pregnancy loss rate was higher (P < .01) in PGF_2α-treated control mares compared with the other groups. There were no differences (P > .1) in pregnancy loss rates among the saline-treated control, Regu-Mate-treated, and BioRelease P4 LA 150-treated mares. These results indicate that intramuscular administration of BioRelease P4 LA 150 containing a total of 1.5 g progesterone every 7 days provided a sufficient level of progesterone to maintain pregnancy between days 18 and 45 of gestation in mares that lacked an endogenous source of progesterone; therefore, this long-acting formulation of progesterone appears to be an efficacious and suitable alternative to currently available progesterone formulations that require daily administration.     

Reproductive Parameters of Mangalarga Marchador Mares in a Commercial Embryo Transfer Programme

The objective of this study is to evaluate the reproductive efficiency in donors and recipient Mangalarga Marchador mares in commercial programmes of embryo transfer (ET) and the effects of some reproductive characteristics and ET methodology on conception rates in the recipient mares. A total of 1140 flushing procedures were performed and 830 embryos (72.8%) were recovered. There were no differences between the rates of embryonic recovery in the different breeding seasons (p > 0.05) and 92.8% of the recovered embryos were 8–9 days old. There was no difference in the embryonic recovery regarding the collection order from the first to the ninth embryo collection along the breeding season, as well as among mares inseminated during the foal heat or subsequent cycles (p > 0.05). Pregnancy rates observed in the total period of all reproductive seasons at 15, 30, 45 and 60 days of pregnancy were 73.4, 69.9, 66.7 and 64.5%, respectively. Differences in pregnancy rate and early embryonic loss rates were not observed between embryos transferred immediately after collection (66.8% and 13.5%) and embryos transported at room temperature for periods of <1 h (62.9% and 14.4%; p > 0.05). Pregnancy rates were higher when the interval between ovulations of donor and recipient mares remained between ?3 and ?2 days (p < 0.05), and the lowest rates were observed for intervals of ?6 days (p < 0.05) with intermediary values for intervals of ?1, 0 and +1 (p > 0.05). Embryonic loss rates, however, did not differ between intervals of ovulation’s synchronism between donor and recipient mares (p > 0.05). This flexibilization in the ovulatory synchronism between donor and recipient mares optimizes the use of recipient mares, thus reducing costs and facilitating management of horse breeding farms.     

The effect of dietary protein on reproduction in the mare. VII. Embryonic development, early embryonic death, foetal losses and their relationship with serum progestagen

Sixty-four Thoroughbred and Anglo-Arab mares aged 6-12 years were randomly allocated to 4 dietary groups and fed diets that differed in the total protein content and quality (essential amino-acids). Forty mares were non-lactating and 24 lactating. Eight mares were withdrawn from the investigation owing to injuries or gynaecological pathology. An overall conception rate of 94.6% and a foaling rate of 80% was achieved. Five of 14 (35.7%) mares (Group 1) fed a low-quality protein diet suffered from early embryonic loss before 90 days of pregnancy compared to 3 of 41 (7.3%) mares in the remaining groups that received the higher-quality protein in their diets. Serum progestagen concentrations of mares in Group 1 that suffered foetal loss were indicative of luteal function insufficiency during the 1st 40 days post-ovulation. Non-lactating mares in all 4 groups gained on average approximately 30 kg in mass during the 90 days before the breeding period. Lactating mares in Group 1 (low-quality protein) lost on average 25 kg in mass during lactation, with no weight loss observed among the lactating mares in the other 3 groups. No difference in the diameter of the embryonic vesicle was found between dietary groups until Day 35 of pregnancy.     

Retained fetal membranes in the mare: A retrospective study

A retrospective study of 3456 deliveries was conducted from the records of four Standardbred broodmare farms where mares were bred by artificial insemination and maintained under close veterinary supervision. Retained fetal membranes (RFM) were observed in 10.6% of the deliveries. Retained fetal membranes occurred more frequently (p < 0.05) after dystocia and in mares which had RFM the previous year. Retained fetal membranes after normal foaling had no significant effect on the reproductive performance (pregnancy rate, pregnancy loss rate, or foaling rate), nor on the general health of the mares, regardless of the duration of RFM (3 to 144 hours). Postfoaling laminitis was not observed. Oxytocin therapy of mares with RFM starting at two hours postpartum significantly reduced the incidence of RFM ≥ 8 hours. Mares with RFM which had received intrauterine antimicrobials between foaling and first breeding had a foaling rate similar to mares with RFM which had not received intrauterine therapy.