Subfertile Mares Research Articles

Progesterone and the pregnant mare: unanswered chestnuts

Equine Veterinary JournalVolume 25, Issue 2 p. 90-91 Free Access Progesterone and the pregnant mare: unanswered chestnuts W. R. ALLEN, W. R. ALLEN TBA Equine Fertility Unit Mertoun Paddocks Woodditton Road Newmarket Suffolk CB8 9BH, UKSearch for more papers by this author W. R. ALLEN, W. R. ALLEN TBA Equine Fertility Unit Mertoun Paddocks Woodditton Road Newmarket Suffolk CB8 9BH, UKSearch for more papers by this author First published: March 1993 https://doi.org/10.1111/j.2042-3306.1993.tb02914.xCitations: 10AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL No abstract is available for this article. References Allen, W.R. (1982) Immunological aspects of the endometrial cup reaction and the effects of xenogeneic pregnancy in horses and donkeys. J. Reprod. Fert., Suppl. 31, 57– 94. Allen, W.R., Kydd, J.H., Boyle, M.S. and Antczak, D.F. (1987) Extraspecific donkey-in-horse pregnancy as a model of early fetal death. J. Reprod. Fert., Suppl. 35, 197– 209. Amoroso, E.C., Hancock, J.L. and Rowlands, I.W. (1948) Ovarian activity in the pregnant mare. Nature. Lond. 161, 355– 356. Bracher, V., Mathias, S. and Allen, W.R. (1992) Videoendoscopic evaluation of the mare's uterus. II. Findings in sub-fertile mares. Equine vet. J. 24, 279– 294. Evans, M.J. and Irvine, C.H.G. (1975) Serum concentrations of FSH, LH and progesterone during the oestrous cycle and early pregnancy. J. Reprod. Fert., Suppl. 23, 193– 200. Irvine, C.H.G., Sutton, P., Turner, J.E. and Mennick, P.E. (1990) Changes in plasma progesterone concentrations from Days 17 to 42 of gestation in mares maintaining or losing their pregnancy. Equine vet. J. 22, 104– 106. Shideler, R.K., Squires, E.L., Voss, J.L., Eikenberry, D.J. and Pickett, B.W. (1982) Progestagen therapy of ovariectomised pregnant mares. J. Reprod. Fert., Suppl. 32, 459– 464. Stewart, F. and Allen, W.R. (1979) The binding of FSH, LH and PMSG to equine gonadal tissues. J. Reprod. Fert., Suppl. 27, 431– 440. Citing Literature Volume25, Issue2March 1993Pages 90-91 This article also appears in:Bibliography: W.R. 'Twink' Allen ReferencesRelatedInformation

Assessment of the breeding prognosis of mares using paired endometrial biopsy techniques

Paired endometrial biopsy samples were taken from 530 subfertile mares, before and after treatment (where indicated) and a period of sexual rest. Prognoses were made after each biopsy (Categories 1A-4A before treatment and Categories 1B-4B after treatment), using histopathological criteria similar to those described by Kenney and Doig (1986). Eighty-seven per cent of the mares were assigned to first biopsy prognosis Category 3A. The second biopsy prognosis produced a more even population distribution (10, 47, 40 and 3 per cent respectively for Category 1B, 2B, 3B and 4B mares). First biopsy Category 3A and 4A mares produced mean foaling rates of 51 and 40 per cent respectively. None of the 14 second biopsy Category 4B mares delivered a live foal (12 were barren, one aborted and one suffered early foetal death). This study supports the hypothesis that a breeding prognosis assigned on the basis of two endometrial biopsy samples, taken before and after specific uterine treatment, where indicated, which takes into consideration the mare's ability to respond to treatment, is likely to be more accurate than one assigned after a single biopsy sample.

Embryo Transfer in Subfertile Mares

Four subfertile mares (at least 2 barren years) were used as donors in an embryo transfer program. The embryo recovery rate was 50%, varying between 0-100. The transfer of 9 embryos resulted in the pregnancy rate of 44%. The efficiency of embryo transfer using subfertile mares is low. In this material 20% of flushings resulted in a pregnancy.

Influence of donor parity and age on the success of commercial equine embryo transfer

SummaryData were compiled regarding the success of commercial embryo recovery rate, transfer pregnancy rate, and embryonic loss in recipients, with respect to influence of donor parity and age, between 1985 and 1988. There were significant differences between maiden and subfertile mares for embryo recovery rate (40/66 versus 81/282), transfer pregnancy rate (34/49 versus 38/78), and embryonic loss in recipients (4/34 versus 13/38). There were also significant differences between recently foaling and subfertile mares (146/276 versus 81/282) and for younger mares (two to eight and nine to 17‐year‐old) compared with older mares (18 to 28‐year‐old) for embryo recovery rates (80/132, 94/183 and 93/309, respectively). Transfer pregnancy rates differed signifiantly between mares aged two to eight‐years‐old compared with those aged nine to 17 and 18 to 28‐years‐old (59/84, 50/97 and 50/90 respectively). No differences were observed among any of the age groups regarding embryonic loss in recipients. There was an effect of year on embryo transfer pregnancy rate in 1985 compared with subsequent years that could have been attributed to any of a wide variety of external factors.

Survival of day-4 embryos from young, normal mares and aged, subfertile mares after transfer to normal recipient mares.

The estimated embryonic loss rate between Days 4 and 14 after ovulation for young, normal mares (9%) was significantly lower (P less than 0.01) than the estimated embryonic loss rate for aged subfertile mares (62%). Fertilization rates, which were based on the recovery of embryos at Day 4 after ovulation, were 96% and 81% (P less than 0.1) for normal and subfertile mares, respectively. Day-4 embryos were collected from the oviducts of normal and subfertile donors mares. These embryos were transferred to the uteri of synchronized, normal recipient mares to test the hypothesis that the high incidence of embryonic loss in subfertile mares was related to embryonic defects. The hypothesis was supported because embryo survival rates were significantly higher (P less than 0.05) for Day-4 embryos from normal compared to subfertile mares. These defects may have been intrinsic to the embryo or might have arisen due to the influence of the oviducal environment before Day 4 after ovulation.

Embryonic Loss in Mares: Incidence, Possible Causes, and Diagnostic Considerations

Fertilization rates were similar for normal and subfertile mares, and much of the difference in fertility between normal and subfertile mares was due to embryonic loss. Fertilization rate estimates for mares ranged from 71 to 96 per cent. The incidence of embryonic loss detected by ultrasonography between Days 11 and 50 was approximately 9 per cent for normal mares, and the estimated incidence of embryonic loss before Day 14 was also 9 per cent. Therefore, the estimated incidence of embryonic loss in normal mares between fertilization and Day 50 is approximately 18 per cent (Fig. 1). In subfertile mares, the corresponding estimate for embryonic loss between fertilization and Day 50 is 80 per cent, with most embryonic losses occurring before Day 14 in subfertile mares (Fig. 1). The high rate of early embryonic loss in subfertile mares could be related to embryonic defects, oviductal environment, or uterine environment. Oviductal embryos from subfertile mares were less viable than embryos from normal mares; therefore, embryonic defects were important in early embryonic losses in subfertile mares. These defects might be inherent within the embryo or might arise from the early oviductal environment. The uterine environment of subfertile mares was adequate to support normal embryos in early gestation; however, the relationship between the uterine environment and the increased metabolic demands of the conceptus in the late embryonic or early fetal periods requires further study. The uterine environment is also altered in mares with endometritis; therefore, endometritis may also be an important factor in embryonic loss in some mares. Uterine-induced luteolysis, as well as the effect of the pathogen or the resulting inflammation, may lead to embryonic loss. An increased susceptibility of some subfertile mares to endometritis could result in embryonic loss secondary to a postcoital endometritis that persists until the embryo reaches the uterus at Days 5 or 6 postovulation. Although progesterone is critical to embryonic survival, the cause-and-effect relationship between progesterone and spontaneous embryonic loss remains unclear. Reduced progesterone concentrations could be related to endometritis, failure of maternal pregnancy recognition, or luteal insufficiency. Progesterone supplementation may be indicated for some mares, but the value of exogenous progesterone for prevention of spontaneous embryonic loss has not been critically tested. A number of other factors have been associated with embryonic loss in mares.(ABSTRACT TRUNCATED AT 400 WORDS)

Use of a low-volume uterine flush for microbiologic and cytologic examination of the mare's endometrium

A guarded uterine swab and a low-volume uterine flush were compared for microbiologic and cytologic examination of the endometrium of young, normal mares (n = 24) and aged, subfertile mares (n = 27). Mares from each group had clitoral sinus swabs, guarded endometrial swabs (X2), uterine flushes and endometrial biopsy samples taken for microbiologic, cytologic and histologic examination. The guarded swab technique yielded significantly fewer (P < 0.05) microbiologic cultures with pathogenic microorganisms than the flush technique for both normal mares ( 0 24 vs 6 24 ) and subfertile mares ( 4 27 vs 14 27 ). The swab technique also yielded significantly fewer (P < 0.05) endometrial smears with cytologic evidence of inflammation than the flush technique for subfertile mares ( 12 27 vs 20 27 ); however, there was no significant difference (P > 0.1) for the two techniques for cytologic results in normal mares ( 3 24 vs 7 24 ). Ureaplasma spp. were isolated from the uterine flushes ( 3 27 ) and clitoral sinus swabs ( 6 27 ) from subfertile mares. Mycoplasma spp. were isolated from the uterine flush from one subfertile mare and clitoral sinus swab from another subfertile mare. Significantly fewer (P < 0.01) normal than subfertile mares had histologic evidence of inflammation in endometrial tissue sections ( 5 24 vs 25 27 ). Based on microbiologic and cytologic results, the low-volume uterine flush appeared superior to the guarded endometrial swab for the diagnosis of endometritis in mares.

Survival of equine embryos transferred to normal and subfertile mares

To test the hypothesis that an abnormal uterine environment was a cause of early embryonic loss in subfertile mares, morphologically normal embryos were transferred to normal mares (n = 20) and subfertile mares (n = 20), and embryo survival rates were compared. Embryos were recovered nonsurgically at Days 7 to 8 postovulation and transferred surgically to normal and subfertile mares that had ovulated on the same day or within 2 d after a donor. Survival of transferred embryos was monitored by ultrasonography of the recipient mare's uterus from Day 9 through Day 28 postovulation. There were no significant differences (P > 0.5) in the embryo survival rates at Day 12 ( 11 20 vs 9 20 ) or Day 28 ( 10 20 vs 8 20 ) for normal or subfertile mares, respectively. The uterine environment of subfertile mares was apparently adequate to support the development of transferred embryos from Days 7 or 8 through Day 28 postovulation.

Survival of day 4 embryos transferred from the oviduct of normal and subfertile donor mares to the uterus of normal recipient mares

Survival of day 4 embryos transferred from the oviduct of normal and subfertile donor mares to the uterus of normal recipient mares

Pregnancy rates at Days 2 and 14 and estimated embryonic loss rates prior to day 14 in normal and subfertile mares

Pregnancy rates at Days 2 and 14 postovulation were determined for 15 normal mares and 15 subfertile mares. Embryonic loss rates were estimated by the difference in the Day 2 and Day 14 pregnancy rates. Mares were artificially inseminated with the pooled ejaculates from three stallions, and the embryonic vesicle was detected with ultrasonography at Days 9, 10, 12 and 14. Mares were short-cycled with prostaglandin F 2 alpha (PGF 2α) and rebred to the same stallions, and the Day 2 pregnancy rates were determined by recovery of cleaved ova (embryos) from the surgically excised oviducts. Significantly more (P < 0.01) normal versus subfertile mares were pregnant at Day 14 ( 12 15 vs 3 15 ). There was no significant difference in the Day 2 pregnancy rate for normal versus subfertile mares ( 10 14 vs 11 14 ). There were no significant differences (P > 0.5) in the mean number of blastomeres per embryo or in the mean diameter of embryos recovered at Day 2 from normal or subfertile mares. The estimated embryonic loss rate was significantly lower (P < 0.01) for normal verusus subfertile mares ( 0 10 vs 8 11 ). Fertilization rates were similar for normal and subfertile mares; however, subfertile mares had a higher embryonic loss rate prior to Day 14 postovulation.

Effect of exogenous progesterone on pregnancy rates after surgical embryo transfer in mares

A completely randomized experimental design was used to investigate the effect of supplemental progesterone on pregnancy rates of recipient mares. Every other recipient mare received daily 200 mg progesterone in oil beginning the day of surgical embryo transfer and lasting until either Day 120 of pregnancy or until pregnancy failure was confirmed by ultrasound. Progesterone supplementation did not affect pregnancy rate (P > 0.05). Overall, embryos that did not result in pregnancy were of greater mean diameter than embryos that resulted in pregnancy (P < 0.05). Pregnancy rates tended (P < 0.1) to be greater in recipients that were detected to be ovulating the same day or prior to that of the donor and that had been supplemented with progesterone (75 %) as opposed to untreated control mares of the same synchrony group (40 %). Progesterone supplementation did not affect the incidence of embryonic loss; however, there was a slightly higher loss of pregnancies between Day 15 and 30 in treated versus untreated recipients. There was no effect (P > 0.05) of treatment on pregnancy rate for embryos recovered from fertile versus subfertile donor mares. However, overall, there tended (P < 0.1) to be fewer pregnancies with embryos recovered from subfertile (50 %) as compared to fertile donors (75 %). It was concluded that supplemental progesterone at the dosage and frequency described was not beneficial in improving pregnancy rates in cyclic recipient mares after surgical embryo transfer.

Recent studies relating to early embryonic death in the mare

SummaryEarly pregnancy loss was studied by sequential ultrasound examinations of 404 pregnancies in commercial brood mares. Overall, the rate of early pregnancy loss was 11.1 per cent. More pregnancies were lost at two to four weeks post ovulation than at four to six or six to eight weeks post ovulation (23 of 45 versus nine of 45 or 10 of 45). The mean (±se) number of days from detection of pregnancy loss until the subsequent ovulation was higher for mares in which pregnancy loss was detected at six to eight weeks post ovulation than at the earlier stages (21.1 ± 3.90 versus 12.0 ± 1.59 or 9.5 ± 1.05, respectively). Thirty‐one of 45 mares that lost pregnancies were subsequently mated; 20 (60 per cent) became pregnant but eight of these pregnancies (40 per cent) were again lost.In a second study a total of 84 embryo collection attempts were made from 14 maiden and 14 subfertile mares. More uterine flushes from maiden mares yielded embryos than from subfertile mares (29 of 42 versus 17 of 42). There were more flushes in which one or more normal embryos were recovered from maiden mares than from subfertile mares (28 of 42 versus eight of 42). There were fewer flushes in which only abnormal embryos were recovered from maiden mares than from sub‐fertile mares (one of 42 versus nine of 42).

Physiological and commercial parameters for producing progeny from subfertile mares by embryo transfer

SummaryThe cost effectiveness of using embryo transfer for producing progeny from subfertile donors is assessed. A total of 146 embryo recovery attempts performed on 34 subfertile donor mares yielded 41 transferable embryos (28 per cent recovery rate) from 27 of these mares. Non‐surgical transfer of these embryos achieved an overall pregnancy rate of 54 per cent. Therefore, the efficiency of producing a pregnancy from sub‐fertile donors was about 15 per cent per mated oestrous cycle. Financial calculations based on cost of materials and the maintenance of recipient mares indicates that a commercial embryo transfer unit would have to charge in excess of US8000 per pregnancy to realise a profit.