Influence of day of postpartum breeding on pregnancy rate, pregnancy loss rate, and foaling rate in Thoroughbred mares

Records (years 2005-2007) were analyzed from a Thoroughbred stud farm in central Kentucky. Data from all breeding cycles of foaling mares were tabulated (3184 cycles of 2003 foaling mares bred between 7 and 163 days postpartum). A multiple logistic regression model employing Bayesian statistics was used to adjust for factors that significantly affected outcome; odds ratios (ORs) for pregnancy rate, pregnancy loss rate, and foaling rate were determined to examine the influence of day of postpartum breeding on these parameters. Mares bred before Day 22 (Day 0 = day of foaling) postpartum had a decreased OR for becoming pregnant (P < 0.05); the median OR for becoming pregnant (1.00) was not reached until Day 46 postpartum. Mares bred before Day 13 postpartum had an increased OR for pregnancy loss (P < 0.05). The median OR for pregnancy loss did not decline below 1.00 until Day 78 postpartum. Mares bred before Day 20 postpartum had a decreased OR for producing a foal (P < 0.05). The median OR for producing a foal (1.00) was not reached until Day 75 postpartum. We concluded that fertility (in terms of a higher OR for becoming pregnant and a lower OR for pregnancy loss, resulting in a higher OR for producing a foal) continued to improve in Thoroughbred mares for approximately 2.5 mo postpartum. These findings are of importance to management strategies directed at early postpartum breeding, and explain some of the reported drift in subsequent foaling dates of Thoroughbred mares, despite management practices that employ early postpartum breeding.     

Body condition during pregnancy and lactation and reproductive efficiency of mares

In Experiment I, 32 mares were equally allotted to the following treatments: mares fed to A) high body condition from 90 days prepartum to foaling and maintained in high body condition to 90 days postpartum, B) high body condition from 90 days prepartum to foaling and allowed to lose body condition to 90 days postpartum, C) lose body condition from 90 days prepartum to foaling and maintained in low body condition to 90 days postpartum, and D) lose body condition from 90 days prepartum to foaling and allowed to gain weight after foaling to attain a high level of body condition by 90 days postpartum. After three cycles, pregnancy rate at 30 days postovulation was lower (P<0.05) in C mares (50%) than in those in the other three groups (100%). Maintenance of pregnancy to 90 days was also reduced (P<0.05) in C mares (25%) when compared with A, D (both 100%) and B mares (88%). Foal growth to 90 days of age was similar in all treatments. In Experiment II, 927 mares were evaluated for body condition and monitored for reproductive performance. Pregnancy rate was lower (P<0.05) and number of cycles/conception was higher (P<0.05) for barren and maiden mares entering the breeding season in thin condition and for pregnant mares foaling in thin condition (condition score less than 5.0) when compared with mares with a higher level of condition. Also, onset of estrus and ovulation appeared to be delayed in barren and maiden mares entering the breeding season in thin condition. Breeding efficiency was enhanced in mares entering the breeding season or foaling at a condition of 5.0 or above. Initial excess stores of body fat enhanced fertility. There were no detrimental effects of excess body fat stored in late gestation.     

Factors affecting the incidence of postpartum oestrus, ovarian activity and reproductive performance in Thoroughbred mares bred at foal heat under Indian subtropical conditions

Decreased reproductive performance due to summer stress is a well known phenomenon in farm livestock. Whether this occurs in the mare and specifically how this might affect postpartum reproductive activity and performance, especially at Foal Heat (FH), is unknown. This study, therefore, aims to investigate this and the factors that might affect postpartum reproductive activity. Reproductive records of 228 Thoroughbred mares (694 mare years) bred in subtropical north-western India were retrospectively analysed. Overt oestrous activity occurred within 21 d postpartum in 92.94% (645/694) of mares. Significantly (p < 0.001) more April foaling mares (97.37%, 185/190) expressed postpartum oestrous activity than those foaling in January (83.61%; 51/61) and February (88.49; 123/139). Similarly significantly (p < 0.01) fewer multiparous mares failed to demonstrate oestrous activity than primiparous mares (6.12% vs.15.07%; 38/621 vs. 11/73, respectively). 190 of these 694 mares were additionally monitored to confirm ovulation; in these mares onset of FH (oestrus plus confirmed ovulation) occurred 8.42 ± 0.17 d and first ovulation 13.64 ± 0.20 d postpartum. Month, stud farm, year, and parity did not affect interval from parturition to FH onset or to first ovulation; or FH onset to ovulation. In FH bred mares Day 16 pregnancy rate and overall foaling rate were 53.76% (100/186) and 46.24% (86/186) respectively and were similar to those of mares bred later postpartum. FH pregnancy rates were not affected by stud, season, month, year, number of matings, or day of ovulation but were significantly (p < 0.008) lowered by increasing mare age. Significantly (p < 0.01) lower Day 16 pregnancy rates were observed in uterine treated mares compared to untreated mares (31.09% vs. 57.96%; 9/29 vs. 91/157, respectively), this difference was not evident during the rest of pregnancy. In conclusion, postpartum reproductive and ovarian activity appears to be affected by environment, i.e., delayed in subtropical kept Thoroughbred mares compared to those kept in temperate climates. However, resulting reproductive performance at FH and the factors affecting postpartum reproductive activity are similar.     

Reproductive performance of Friesian mares after retained placenta and manual removal of the placenta

Because the incidence of retained placenta in Friesian mares is estimated to be high, and no reports have been published on the reproductive performance of Friesian mares after retained placenta, we studied postpartum reproductive performance in Friesian brood mares with (n = 54) and without (n = 50) retained placenta. We defined a retained placenta as the failure to expel all fetal membranes within 3 h after the delivery of a foal. We subdivided the group of mares with retained placenta into mares in which the placenta had been removed manually (n = 30) and mares in which it had not (n = 24). Within each group, we compared reproductive performance after breeding in the foal heat and breeding in a subsequent heat. We also recorded the age of the mares, number of mares treated with antibiotics after insemination, and number of mares treated with prostaglandins. The interval between delivery and conception, efficacy rate (number of served cycles divided by the number of mares that had a positive pregnancy diagnosis), seasonal pregnancy rate, pregnancy rate after first insemination, pregnancy loss rate, and foaling rate did not differ between mares with and without retained placenta or between mares with and without manual removal of the retained placenta. Within each group, the pregnancy rate after first insemination did not differ between breeding for the first time in the foal heat and breeding for the first time in a subsequent heat. We concluded that reproductive performance did not differ between (1) Friesian mares with and without retained placenta and (2) Friesian mares with and without manual removal of the placenta. With regard to reproductive performance, retained placenta and manual removal of the placenta are not valid reasons to avoid foal heat breeding in Friesian mares.     

The effects of different insemination regimes on fertility in mares

This study investigated the effects of different artificial insemination (AI) regimes on the pregnancy rate in mares inseminated with either cooled or frozen-thawed semen. In essence, the influence of three different factors on fertility was examined; namely the number of inseminations per oestrus, the time interval between inseminations within an oestrus, and the proximity of insemination to ovulation. In the first experiment, 401 warmblood mares were inseminated one to three times in an oestrus with either cooled (500 x 10(6) progressively motile spermatozoa, stored at +5 degrees C for 2-4 h) or frozen-thawed (800 x 10(6) spermatozoa, of which > or =35% were progressively motile post-thaw) semen from fertile Hanoverian stallions, beginning -24, -12, 0, 12, 24 or 36 h after human chorionic gonadotrophin (hCG) administration. Mares were injected intravenously with 1500 IU hCG when they were in oestrus and had a pre-ovulatory follicle > or =40mm in diameter. Experiment 2 was a retrospective analysis of the breeding records of 2,637 mares inseminated in a total of 5,305 oestrous cycles during the 1999 breeding season. In Experiment 1, follicle development was monitored by transrectal ultrasonographic examination of the ovaries every 12 h until ovulation, and pregnancy detection was performed sonographically 16-18 days after ovulation. In Experiment 2, insemination data were analysed with respect to the number of live foals registered the following year. In Experiment 1, ovulation occurred within 48 h of hCG administration in 97.5% (391/401) of mares and the interval between hCG treatment and ovulation was significantly shorter in the second half of the breeding season (May-July) than in the first (March-April, P< or =0.05). Mares inseminated with cooled stallion semen once during an oestrus had pregnancy rates comparable to those attained in mares inseminated on two (48/85, 56.5%) or three (20/28, 71.4%) occasions at 24 h intervals, as long as insemination was performed between 24 h before and 12 h after ovulation (78/140, 55.7%). Similarly, a single frozen-thawed semen insemination between 12 h before (31/75, 41.3%) and 12 h after (24/48, 50%) ovulation produced similar pregnancy rates to those attained when mares were inseminated either two (31/62, 50%) or three (3/9, 33.3%) times at 24 h intervals.In the retrospective study (Experiment 2), mares inseminated with cooled semen only once per cycle had significantly lower per cycle foaling rates (507/1622, 31.2%) than mares inseminated two (791/1905, 41.5%), three (464/1064, 43.6%) or > or =4 times (314/714, 43.9%) in an oestrus (P< or =0.001). In addition, there was a tendency for per cycle foaling rates to increase when mares were inseminated daily (619/1374, 45.5%) rather than every other day (836/2004, 42.1%, P = 0.054) until ovulation.It is concluded that under conditions of frequent veterinary examination, a single insemination per cycle produces pregnancy rates as good as multiple insemination, as long as it is performed between 24 h before and 12 h after AI for cooled semen, or 12 h before and 12 h after AI for frozen-thawed semen. If frequent scanning is not possible, fertility appears to be optimised by repeating AI on a daily basis.     

Reproductive efficiency of Thoroughbred mares under Indian subtropical conditions: A retrospective survey over 7 years

Service records of 253 mares (1181 mare-years) spanning over 7 consecutive years, from nine organized Thoroughbred stud farms, situated in the subtropical northwestern India were retrospectively analyzed to assess their reproductive performance. The overall per cycle pregnancy rate at Day 16 and overall foaling rates were 50.30% and 68.95%, respectively, and were significantly higher in mares aged 3–7 years than ≥18 years old mares. The late embryonic losses (9.86%) that occurred between Days 16 and 39 post-ovulation contributed more than 50% of the overall detected pregnancy losses (19.11%). The overall percent detected pregnancy losses were lower in mares at ages 3–7 years compared to those at ages ≥18 years (14.78% vs. 46.43%, respectively; P < 0.0001). Chronic barren and habitual aborter mares tended to affect reproductive efficiency of mares. Fifty percent of the mares that experienced ≥2 consecutive abortions or barren years, again stayed aborted or barren in the next seasons, respectively. No effect of numbers of matings per oestrus was observed on overall fertility. Neither the induction of oestrus nor ovulation by exogenous hormonal treatment had any effect on most of the analyzed reproductive parameters. Regarding breeding month or years, the reproductive efficiency did not differ significantly. The incidence of multiple pregnancies was 5.40% and percent late embryonic loses were higher (P = 0.0016) in twin (21.98%) than singleton (8.64%) pregnancies. In conclusion, comparatively lower fertility rates were recorded in Thoroughbred mares bred under Indian subtropical climatic conditions than those reported from temperate regions that might be due to difference in breeding management rather than prevailing environment.     

Biodegradable estradiol microspheres do not affect uterine involution or characteristics of postpartum estrus in mares

Quarterhorse mares were used to investigate effects of estradiol-17beta on uterine involution, duration of estrus, interval to ovulation, and fertility achieved by breeding on the first postpartum estrus. On the day of foaling, mares were injected with biodegradable poly (DL-lactide) microspheres containing either 100 mg estradiol-17beta (25 mares) or no drug (27 mares). The treatment period was considered to last for 12 to 15 d. Estrus was determined by teasing mares (n=16) with a stallion. Ovulation was detected by transrectal ultrasonographic examination of ovaries (n=48). On Days 6, 11 and 16 post partum, transrectal ultrasonography was used to measure cross-sectional diameters of the uterine body, uterine horns, and fluid within the uterine lumen (n=28). Uteri were swabbed for bacteriologic culture, and uterine biopsies were obtained from the previously gravid uterine horn on Days 11 and 16 post partum, for assessment of endometritis and morphometric analysis of endometrial histioarchitecture (n=19). Twenty-two mares were bred on foal-heat, and pregnancy was determined by transrectal ultrasonography on 14 to 16 and 30 to 35 d after breeding. With only one exception (diameter of previously gravid uterine horn on Day 11), mean values for all measures of uterine involution did not differ between treatment groups (P > 0.05). No differences were detected between treatment group means for length of estrus or interval to ovulation (P > 0.05). No differences were detected between treatment group liklihoods for recovery of potential bacterial pathogens, presence of endometritis, or presence of intrauterine fluid at 11 or 16 d post partum (P > 0.05). Pregnancy rate of mares treated with estradiol (5 11 ; 45%) was not different from that of control mares (9 11 ; 82%; P > 0.05). Estradiol treatment did not hasten uterine involution, increase duration of estrus, delay ovulation, or increase fertility in these postpartum mares.     

Reproductive management of mares without detection of oestrus.

The use of photoperiod, progestagen, prostaglandin and hCG treatments was investigated to obtain mating of mares at predetermined times. The objectives were: (1) synchronization of oestrus at an early time of the year, (2) simplification of treatment schedules by use of vaginal sponges, and (3) use of several controlled cycles by successive synchronization. The following conclusions were reached. First, after a 16 h photoperiod was applied beginning on 25 November, hormonal synchronization of oestrus and ovulation followed by cyclicity were obtained on 1 February; i.e. 2 months of light are essential as hormonal synchronization of ovulation was not obtained by 10 January. Second onset of oestrus was well synchronized after vaginal application of progestagens (3.75 days +/- 0.98 s.d. after withdrawal) and in spite of vaginal irritation, fertility was high (71%, N = 24) after mating every 48 h of the induced oestrus. Third, for synchronization of return to oestrus in mated non-conceiving mares, oral progestagens were given from Days 7 to 21 after mating. Predetermined mating (Days 27 and 29) and hCG injection (day 28) for non-pregnant animals were decided after a progesterone assay of Day 21 blood plasma. After 3 controlled mating periods, the cumulative fertility was 88% (N = 24) in non-lactating mares and 58% (N = 19) in lactating mares. Programmed reproductive management is possible in the horse.     

Effect of oestrus synchronization methods on oestrus behaviour, timing of ovulation and pregnancy rate during the breeding and low breeding seasons in Nili-Ravi buffaloes

The objective of this study was to determine the effect of oestrous synchronization methods on oestrous behaviour, timing of ovulation and pregnancy rate during the breeding and low breeding seasons in Nili-Ravi buffaloes. In Experiment 1, oestrous behaviour and timing of ovulation were determined from (n=34) oestruses. The mean (+/- S.E.M.) time of ovulation after the onset of standing oestrus was greater (P<0.05) in PGF(2alpha)-induced luteolysis (30.6+/-1.5h) compared to Ovsynch buffaloes (15.0+/-0.8h). In Experiment 2, pregnancy rates were compared between two methods of synchronization (detected oestrus and Ovsynch protocol) during the breeding and low breeding seasons. Pregnancy rates of buffaloes bred at detected oestrus (62.5%) or by the Ovsynch protocol (36.3%) during the breeding season did not differ significantly (P>0.05) from those which were inseminated during the low breeding season (55.5%) and (30.4%), respectively. This study demonstrates clearly that (1) timing of ovulation in Nili-Ravi buffalo is about 30h after the onset of standing oestrus and (2) buffaloes can be successfully synchronized with optimum fertility using either PGF(2alpha) alone (detected oestrus) or using (Ovsynch protocol) during low breeding season, to calve during the period when milk availability is short.     

The effects of prostalene and alfaprostol as uterine myotonics, and the effect on postpartum pregnancy rate in the mare following daily treatment with prostalene

The effects of oxytocin and two prostaglandin (PG) F(2)alpha analogues, prostalene and alfaprostol, on uterine pressure in the mare were measured using balloon-tipped catheters connected to pressure transducers. The PGF(2)alpha analogues caused increased uterine pressure beginning 7 to 15 min postinjection and persisting for the duration of each 60 min recording session. Forty postpartum mares of light-horse breed were used to evaluate the effects of prostalene on postpartum pregnancy rate. Eighteen mares were injected by aseptic technique subcutaneously with 1 mg prostalene twice daily, beginning on the day of foaling (Day 0) and continuing for 10 consecutive days (Day 10) or until the mare was first bred at foal heat. Twenty-two postpartum mares were injected with 1.0 ml sterile saline by the same technique as the controls. Of treated mares, 76.9% were diagnosed pregnant after breeding versus 44.4% of the control mares (P = 0.07). Of treated mares, 66.7% bred at their second postpartum estrus became pregnant versus 28.6% of control mares (P = 0.03). Prostalene, given at 1 mg twice daily for 10 d postpartum, produced an increased pregnancy rate after both foal heat and second postpartum estrus breedings in the mare.     

Management and fertility of mares bred with frozen semen.

Semen quality, mare status and mare management during estrus will have the greatest impact on pregnancy rates when breeding mares with frozen semen. If semen quality is not optimal, mare selection and reproductive management are crucial in determining the outcome. In addition to mare selection, client communication is a key factor in a frozen semen program. Old maiden mares and problem mares should be monitored for normal cyclicity and all, except young maidens, should have at least a uterine culture and cytology performed. Mares with positive bacterial cultures and cytologies should be treated at least three consecutive days when in estrus with the proper antibiotic. With frozen semen, timing the ovulation is highly desirable in order to reduce the interval between breeding and ovulation. The use of ovulation inducing agents such as human chorionic gonadotropin (hCG) or the GnRH analogue, deslorelin, are critical components to accurately time the insemination with frozen semen. Most hCG treated mares ovulate 48h post-treatment (12-72h) while most deslorelin (Ovuplant) treated mares ovulate 36-42h post-treatment. However, mares bred more than once during the breeding cycle appear to have a slight but consistent increase in pregnancy rate compared to mares bred only once pre- or post-ovulation. In addition, the "capacitation-like" changes inflicted on the sperm during the process of freezing and thawing appear to be responsible for the shorter longevity of cryopreserved sperm. Therefore, breeding closer to ovulation should increase the fertility for most stallions with frozen semen. Recent evidence would suggest that breeding close to the uterotubal junction increases the sperm numbers in the oviduct increasing the chances of pregnancy. Post-breeding examinations aid in determining ovulation and uterine fluid accumulations so that post-breeding therapies can be instituted if needed. Average pregnancy rates per cycle of mares bred with frozen semen are between 30 and 40% with a wide range between sires. Stallion and mare status are major factors in determining the success of frozen semen inseminations. Pregnancy rates are lower for barren and old maiden mares as well as those mares treated for uterine infections during the same cycle of the insemination. To maximize fertility with frozen semen, a careful selection of the stallions and mares, with proper client communication is critical. Dedication and commitment of mare owner and inseminator will have the most significant impact on the pregnancy rates.     

Equine antisperm antibodies (EASA): Preliminary study of the clinical response following breeding in immunized mares

Maiden mares (n=6), previously injected with stallion sperm cells (SC group, N=2), stallion seminal plasma (SP group, N=2), or phosphate-buffered saline as a control (C group, N=2) were followed through 5 consecutive estrous cycles to evaluate their clinical response when exposed to stallion sperm cells via breeding. Management was similar to that expected on typical breeding farms. The mares were teased daily and bred by artificial insemination (AI) in all 5 cycles. Differences in serum and uterine flushing equine antisperm antibody (EASA) levels, endometrial culture and cytology results, endometrial biopsy score and fertility were evaluated between treatment groups. An enzyme-linked immunosorbant assay (ELISA) was used to determine serum and uterine IgG and IgA levels specific for sperm cell or seminal plasma antigens. Serum IgG specific for sperm cell antigen was higher in the SC group than in the SP and C groups following exposure to sperm cells via breeding (P<0.05). All other EASA levels were not different between groups (P>0.05); however, uterine IgA levels in one of the SC treated mares did rise over all 5 cycles. No differences were detected in culture, cytology, biopsy or fertility results between groups (P>0.05). Changes in EASA levels were detected after breeding mares previously immunized with stallion sperm cells, however an associated clinical response was not apparent.     

The relationship between consecutive pregnancies in Thoroughbred mares. Does the location of one pregnancy affect the location of the next, is this affected by mare age and foal heat to conception interval or related to pregnancy success

Delayed uterine involution is a major cause of early reproductive failure in mares. Involution is affected by mare age, and foaling to covering interval. Involution rates vary between the previously non-gravid horn (PNGH), which recovers the quicker, and the previously gravid horn (PGH). Location of a pregnancy and its likely success may, therefore, be affected by its location relative to the previous pregnancy. This study aimed to determine: (i) the location of concepti in consecutive pregnancies; (ii) whether this varies with mare age or foaling to conception interval; (iii) whether location in relation to the previous pregnancy affects success. 1383 Thoroughbred mares were monitored by ultrasonic scanning during oestrus and early pregnancy. Significantly (p < 0.01) more pregnancies were located in the PNGH (79.2%) than the PGH (20.8%). The number of pregnancies in PGH significantly increased with mare age (p < 0.01) and foaling to conception interval (p < 0.05). Significantly (p < 0.001) more pregnancies located in the PGH (16.5%) failed, than those in the PNGH (4.6%). It can be concluded that most pregnancies locate in the PNGH where their chances of success are greatest. The larger number of pregnancies locating in the PGH in older mares and those with shorter foaling to conception intervals may in part account for the higher conceptus mortality rates in such mares. Hence breeding older mares on alternate years and maximising foaling to conception interval may improve reproductive success. Alternatively termination of pregnancies located in the PGH followed by timely recovering may be justifiable as might ET in older mares covered close to foaling.     

Perceptions of obesity in a UK leisure-based population of horse owners

Pregnancy rates with cooled equine semen can be unsatisfactory and show great variation. Information about first cycle pregnancy rates and pregnancy rates per cycle are often lacking from publicly available records. This retrospective cohort study was performed to evaluate the fertility of the Norwegian Coldblooded trotter. The aim of the study was to compare the breeding results after insemination with fresh, extended with those of cooled, shipped semen among Norwegian Coldblooded trotter mares. First cycle pregnancy rate was the main parameter used to measure fertility. Stud-books were collected from four studs from the years 2006–2010. Statistical analyses were done in Stata using Chi square test and multivariable analyses where different models were compared based on Akaike’s information criterion. First cycle pregnancy rate, seasonal pregnancy rate and foaling rate all showed significant differences (P < 0.0001) when comparing mares inseminated at stud with mares inseminated with cooled, shipped semen, favoring artificial insemination (AI) at stud. First cycle pregnancy rate was 55.1 % for mares inseminated at stud with fresh extended semen and 42.2 % for mares inseminated with cooled shipped semen. The overall pregnancy rate per cycle was 84.4 % for AI at stud and 66.9 % for cooled, shipped semen. The parameters stud, mare age, number of inseminations within an estrus cycle and individual stallion were also investigated for influence on fertility. Few retrospective studies include the parameter of first cycle pregnancy rates. Our study does not differ dramatically when comparing seasonal pregnancy rates and foaling rates with similar studies. Fertility parameters for the Norwegian Coldblooded trotter do not differ significantly from most other studies of Coldblooded mares and other mare breeds around the world. But the difference in fertility parameters between AI at stud to AI with cooled semen between our study and others, indicates that higher pregnancy rates in Norwegian Coldblooded trotter may be possible.     

Retained placenta in Friesian mares: incidence, and potential risk factors with special emphasis on gestational length

During the foaling seasons of 1999 and 2000, the incidence of retained placenta in 495 normal parturitions of 436 Friesian brood mares was studied. Retained placenta was defined as a failure to expel all fetal membranes within 3 h of the delivery of the foal. Furthermore, the sex of the foal, month of breeding, sire and dam's sire, age of the mare, and time of day of foaling, were studied as factors that might be associated with retained placenta in Friesian mares after normal foalings, and with gestational length. The analysis was carried out using marginal logistic regression, and mixed linear regression, respectively. The incidence of retained placenta was 54%. Mean length of gestation was 331.6 days. Colts were carried 1.5 days longer than fillies. Mares bred in July-September had a 4-day shorter gestation period (329 days) than mares bred earlier in the year. There was a mare, sire, and dam's sire effect on gestational length, and a mare effect on the occurrence of retained placenta. Mares foaling at 4 and >17 years of age, tended to have a lower incidence of retained placenta than mares foaling at 5-17 years of age. No association was found between the occurrence of retained placenta, and gestational length, sex of the foal, month of breeding, dam's sire, and time of day of foaling. It was concluded that the observed high incidence of retained placenta indicates that the Friesian breed of horses has a higher risk for retained placenta than other breeds of horses.     

Recovery Rate and Quality of Embryos from Mares Inseminated at the First Post-Partum Oestrus

The pregnancy rate is lower in mares inseminated at the first post-partum (p.p.) oestrus (40-50%) compared with pregnancy rates in subsequent oestrous cycles (55-65%). The causes of the lowered pregnancy rate are not fully understood. The aim of the present study was to examine if embryonic defects could be one of the reasons for lowered pregnancy rate. A total of 23 p.p. and 14 non-lactating control mares were flushed 7 days after detection of ovulation. Embryo recovery rate was 48% and 71% in p.p. and control mares, respectively (p=0.16). Embryos were photographed, measured, graded and stained with fluorescein diacetate to assess their viability. Thereafter embryos were bisected and stained with Hoechst 33342 to count the cell nuclei. Embryos in both groups were equally viable and the cell numbers were not significantly different. According to morphological evaluation all embryos were classified as excellent or good. Embryos aged 7.3 to 7.6 days (± 0.25 days) were smaller in the p.p. group than in the control group (p<0.05). Forty-seven (9/19) and 8% (1/13) of the uterine swabs, taken before the first insemination, yielded bacteria and neutrophils in p.p. and control mares, respectively. The amount of neutrophils and/or bacteria had no statistically significant effect on embryo recovery rate (p>0.10). Recovery of embryos was not related to histological findings in uterine biopsies taken after embryo recovery. Embryo recovery rate in p.p. mares (48%) was similar to previously reported foal heat pregnancy rates (40- 50%). Hence, early embryonic death in utero would not be the most likely reason for lowered pregnancy rate in mares inseminated at the first p.p. oestrus. Sperm transport and oviductal conditions by the time of the first p.p. oestrus would need to be studied to clarify the role of fertilisation failure as the cause of lower pregnancy rate in mares inseminated at foal heat.     

Dynamics of activities of matrix metalloproteinases-9 and -2, and the tissue inhibitors of MMPs in fetal fluid compartments during gestation and at parturition in the mare

During late gestation in the mare, rapid fetal growth is accompanied by considerable placental growth and further invasion of the endometrium by microvilli. This growth requires extensive remodeling of the extracellular matrix (ECM). In early pregnancy, we know that matrix metalloproteinase (MMP)-9 and -2 are involved in the endometrial invasion during endometrial cup formation. The present study investigated whether MMPs are found in fetal fluids later in gestation and during parturition, and if there was a difference in their activities between normal and preterm delivery. Amniotic fluids were collected from pony mares during the latter half of gestation, and amniotic and allantoic fluids from pony and thoroughbred mares at foaling. The fluids were analysed for the activity of MMP-9 and -2, and TIMPs using zymography techniques. There was an increase (P = 0.002) in activity of latent MMP-9 when approaching normal foaling, and a decrease (P < 0.001) during foaling. MMP-2 activity did not change through gestation, or during foaling. When comparing samples from pregnancies resulting in preterm deliveries with samples from foaling mares, the activity of MMP-9 was lower (P < 0.001) and MMP-2 activity was higher (P = 0.004) during foaling than preceding preterm delivery. The activity of MMP-9 was lower (P = 0.002) prior to preterm delivery than before delivery of a live foal at term, whereas no difference (P = 0.07) was demonstrated for latent MMP-2 activity when comparing the same groups. The activity of TIMP-2 was higher (P < 0.001) in the pre-parturient period before normal foaling than preceding preterm delivery. These results suggest that MMPs may have a role as markers for high risk pregnancy in the mare.     

Postpartum reproductive performance in the multiparous mare fed to obesity

Twenty multiparous Quarter Horse mares were assigned to one of two treatment groups at 40 to 75 d of pregnancy. Group 1 was the control group and the mares were fed to maintain a moderate degree of body fat (condition score 5.5 to 7). Group 2 was the obese group and the mares were fed to achieve (prepartum) and then maintain (post partum) an extremely high degree of body fat (condition score 9). Estrous intensity was evaluated using subjective teasing scores ranging from 0 (rejection) to 4 (maximum receptivity). Mares were artificially inseminated beginning with the second postpartum ovulatory cycle; the study was terminated after 63 d of pregnancy. Duration of estrus, maximum teasing score and the number of mares exhibiting overt estrus (teasing score > 2) did not differ between treatment groups during the first and second postpartum ovulatory cycles. The intervals from foaling to first cycle ovulation, foaling to second cycle ovulation, and first to second cycle ovulation were also similar between treatment groups. All mares in both treatment groups conceived and maintained pregnancy. The first cycle conception rate and the number of cycles per conception did not differ between treatment groups. A high degree of body fat produced by overfeeding during gestation did not adversely affect postpartum reproductive performance in the multiparous mare.     

Use of a semen extender containing antibiotic to improve the fertility of a stallion with seminal vesiculitis due to Pseudomonas aeruginosa

A breeding trial was conducted to determine if a semen extender containing polymixin-B sulfate would improve the fertility of a stallion with seminal vesiculitis due to Pseudomonas aeruginosa . Twenty-three mares were bred to the stallion by one of three methods: artificial insemination with raw semen (Group 1, n = 10), artificial insemination with semen mixed 1:1 with a nonfat dry skim milk/glucose extender containing 1000 units/ml polymixin-B sulfate (Group 2, n = 9), or natural service immediately following infusion of the uterus with 100 ml of the same extender (Group 3, n = 4). Artificial breedings contained a minimum insemination dose of 500 x 10(6) progressively motile spermatozoa. All mares were bred every other day while in estrus. Pregnancy status was determined by transrectal ultrasound examination 15 d after the last breeding. First-cycle pregnancy rate for Group 2 mares (78%) was greater (P < 0.01) than for Group 1 mares (10%). There was a tendency (P = 0.10) for the pregnancy rate of Group 3 mares (50%) to be greater than Group 1 mares. The use of a semen extender containing polymixin-B sulfate improved the fertility of this stallion.     

Plasma prolactin concentrations and cyclic activity in pony mares during parturition and early lactation

Five pony mares were blood sampled during late pregnancy, foaling and early lactation. An homologous assay for horse prolactin was used to measure plasma prolactin concentrations in these samples. Regular estimates of cyclic activity were also made. Plasma prolactin concentrations rose markedly in the last week of pregnancy and remained high although variable in early lactation, before declining to basal levels by 1-2 months post partum. All mares showed a post-partum oestrus 7.0 +/- 0.9 days after parturition. One mare whose foal died shortly after birth showed a rapid decline in plasma prolactin values after death of the foal and an early oestrous period (4 days after parturition). The pattern of prolactin changes reported for the mare are in agreement with those reported for other mammalian species.