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Summary Two mares being monitored in a project concerning early foetal death failed to maintain their pregnancies despite improved management. They repeatedly lost their conceptuses so one was treated with allyl trenbolone and the other with flunixin meglumine from Day 10 of gestation. Treatment with allyl trenbolone until Day 70 of gestation maintained pregnancy despite regression of the primary corpus luteum and the resulting low levels of endogenous progesterone in peripheral plasma during one month; secondary corpora lutea developed at the expected time. In the other mare with a history of premature release of prostaglandin F2α, treatment with flunixin meglumine until Day 60 of gestation inhibited prostaglandin F2α synthesis and luteal function was maintained.

Summary In the mare, there is a high incidence of early embryonic mortality which corresponds to early conceptus development and the time of maternal recognition of pregnancy. The need for synchrony between the developing conceptus and the uterine environment emphasises the delicate processes of establishment and maintenance of pregnancy. Further research is necessary to investigate the environments of the conceptus and uterus, and their interaction, for a better understanding of these processes and ultimately a reduction in early embryonic loss.

Contents Over a 25-month period 8118 blood samples were assayed for the presence of the serum pregnancy specific-protein B (PSPB) and progesteron (P4) concentrations on three Hungarian large-scale dairy farms. Pregnancy (n = 4085) was checked by BioPRYN assay at 30–36 days post-insemination (PI). Samples from all cows that tested not pregnant and from cows with an optical density (OD) reading in the BioPRYN test that was between 0% and 30% above the cutoff OD value were tested for serum P4 concentration. According to serum P4 concentration, cows were assigned to three categories: high (>4 ng/ml), medium (2–4 ng/ml) and low (

Summary The overall live foaling percentage per cycle on 4 Kentucky Thoroughbred farms was 42.0%. The rate varied with mare reproductive status, mare age, cycle number and stallion. The most pronounced effect was associated with mare age. Estimates of the relative importance of embryonic loss as a factor limiting reproductive success for young and old mares. suggest that young mares lose half of their embryos from fertilisation to term, and the loss rate increases with mare age to the point that old mares lose all or nearly all of their embryos.

Human gamete chromosome studies using 702 oocytes and 15,864 spermatozoa were reviewed. These studies were chosen because they were carried out with our improved chromosomal technique, the gradual fixation-air drying method, which has been proven to be very reliable. The incidence of aneuploidy was about eight times as high in the oocytes (11.0%) as in the spermatozoa (1.4%), whereas that of structural chromosome aberrations was three times as high in the spermatozoa (14.1%) as in the oocytes (4.7%). In the spermatozoa, segregation errors leading to aneuploidy were found randomly among eight chromosome groups (A-G and sex chromosome). In contrast, they did not occur randomly in the oocytes. The observed frequency was significantly higher in group G and significantly lower in group A, as compared with the theoretical frequencies which were calculated according to the assumption that the segregation errors had taken place with an equal chance in each of 23 chromosomes. About 60% of the segregation errors were found to be due to so-called nondisjunction (loss or gain of dyads) and about 40% were due to so-called predivision (loss or gain of monads). The incidence of aneuploid oocytes increased slightly with the increase of donor age, although showing no statistical significance. The incidence of spermatozoa with structural chromosome aberrations vaned considerably from donor to donor (3.6–24.8%). However, there was no positive correlation between the occurrence of these spermatozoa and the age of donors or the habit of smoking. Incidences of chromosome aberrations in the human gametes (22.8% in oocytes and 15.5% in spermatozoa) were far higher than those in experimental animals. These seem to be associated closely with the characteristics of human reproduction and are responsible for a great part of human embryonic loss and developmental anomalies.

Summary Data 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.

The chromosome complement and anatomical development of 10–16-gday rabbit embryos were studied following delayed fertilization. Preimplantation loss was 40% in the experimental group compared with 17% in control animals. Also, a greater number of embryos retarded in growth or with structural anomalies was seen in the delayed-mated group. Cytogenetic analysis revealed a trisomy for a small metacentric chromosome in 104 control embryos. Only 1 triploid embryo was found in 84 implantation sites from rabbits that had been delayed mated. The incidence of triploidy postimplantation was much less than the 13% found previously in 6-day blastocysts. Increased embryonic loss at the time of or shortly after implantation may be responsible for the discrepancy.

Normal pregnant guinea pigs were killed on gestation days 12–20 and examined for implantation sites and resorbing embryos. Their ovaries were removed and serially sectioned, and the functioning corpora lutea counted for comparison with the number of conceptuses. It was found that a single corpus luteum was associated with two implantation sites with a frequency of 9.55%. Embryonic loss prior to implantation was 12.6% and the value for resorption following implantation varied from 5.8 to 7.2% depending on the time of killing and the method employed for determining resportion. A count of functioning corpora lutea facilitated the determination of embryonic loss prior to implantation, but offered little advantage over simpler techniques for determining resorption after implantation.