SummaryThe findings of a retrospective survey of 1393 Thoroughbred mares visiting 22 studfarms in the Newmarket region of the United Kingdom during the 1998 covering season were compared with those of a similar study undertaken 15 years earlier in 1983. The effects of mare age and status, the stallion, the month of mating, the 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. Keywords:equine pregnancy, pregnancy loss, foaling rate, twins

ResearchA growing equine conceptus must suppress the cyclical release of PGF 2α from the endometrium to effect maternal recognition of its presence in the uterus. Paradoxically, the conceptus itself secretes PGF 2α , together with other prostaglandins. In this study, the PGF 2α and PGE 2 content of, and production in vitro by, day 10-32 equine conceptuses were measured and the influence of pregnancy on the concentrations of these prostaglandins in the uterine lumen was examined. In vitro, the release of both prostaglandins per mg conceptus tissue was very high on day 10 after ovulation and lower thereafter. However, while PGF 2α production decreased further after day 18 of gestation, PGE 2 production remained high until day 32. Prostaglandin concentrations in yolk sac fluid were unaffected by gestational age and PGE 2 concentrations in this compartment were two to five times higher than PGF 2α concentrations. PGF 2α concentrations reached high values in uterine flushings recovered from cyclic mares during days 14-16 after ovulation, the expected time of luteolysis, but were negligible in flushings recovered from pregnant mares at this time. Beyond day 18 of gestation, PGF 2α concentrations in uterine flushings were high and strikingly similar to those recorded during cyclical luteolysis. It is concluded that the equine conceptus effects maternal recognition of pregnancy primarily by inhibiting the ability of the endometrium to release PGF 2α during days 12-16 after ovulation. However, the conceptus appears to delay, rather than prevent, the development of the uterine PGF 2α release pathway and an alternative mechanism must prevent luteolysis from being triggered during days 18-32 of gestation.

Peripheral serum samples were collected from 8 pregnant dromedary camels and hormone secretion patterns were examined at specific time intervals. Mean serum progesterone concentrations began to rise 3-4 days after ovulation and remained reasonably constant at 3-5 ng mL-1 for the first 90-100 days of gestation. Concentrations then showed a definite fall, but thereafter remained constant again at 2-4 ng mL-1 throughout the rest of pregnancy. In contrast, serum oestrogen concentrations showed pronounced fluctuations during the first 100 days of gestation. Mean oestradiol-17 beta concentrations increased at around Day 50 to about 100 pg mL-1 and then remained relatively constant from Day 90 to Day 300. Mean oestrone sulfate concentrations, however, showed two definite peaks in early gestation, each reaching about 10 ng mL-1, with the first peak occurring around Day 25 and the second peak around Day 75. Oestrogen production then remained fairly constant until around Day 300, after which concentrations of both oestrone sulfate and free oestradiol-17 beta rose steeply over the next 80 days to reach mean peak values of 46 ng ML-1 and 518.7 pg mL-1, respectively, at the time of parturition. Concentrations of 13,14 dihydro-15-keto prostaglandin F2 alpha (PGFM) remained low and reasonably steady at 100-200 pg mL-1 during the first 320 days of pregnancy; thereafter, PGFM concentrations rose steeply over the next 50 days, before an explosive further increase to a peak of 1900 +/- 141 pg mL-1 mean +/- sem on the day of calving. These results suggest that, as in the cow, a major change in steroid synthetic capability and/or enzyme content of the placenta may occur at around 80% (Day 300) of gestation in the pregnant camel.

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SummaryIt has been proposed that oestrogen secreted in large quantities by the rapidly expanding blastocyst is responsible for maternal recognition of pregnancy in the mare, as it is in the sow. However, while exogenous oestrogen administration readily prolongs luteal lifespan in dioestrous sows, the recorded effects on dioestrous mares have ranged from the predicted luteostasis to a diametrically opposed, hastened luteolysis. One possible explanation for the contrary results is that, as in the domestic ruminant species, oestrogens (of ovarian origin) actually help to establish the luteolytic cascade. If so, high systemic oestrogen concentrations might be expected to compromise rather than to protect early pregnancy, and there is some evidence that this may be the case. On the other hand, conceptus oestrogens almost certainly have important local intra-uterine effects, for example on myometrial activity, vascularity and endometrial gland secretion, all of which are essential to equine conceptus development. Keywords:pregnancy, mare, oestrogen, conceptus, luteolysis