Summary 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.

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

Endometritis in the mare begins as a normal physiological inflammatory response to breeding that involves both a mechanical and immunological response pathway activated to rid the uterus of semen and bacteria. With successful resolution of this inflammation, the mare’s uterus will provide a hospitable environment for the development of the semi-allogenic conceptus. If the mare fails to resolve this inflammatory response within 48 hours of breeding, she will become susceptible to persistent breeding induced endometritis (PBIE) which will have detrimental effects on her fertility. This condition can then predispose the mare to bacterial or fungal endometritis leading to further degeneration of the endometrium. Optimisation of the mare’s fertility requires a fine balance between allowing the natural immune response of the endometrium to its exposure to allogenic semen to run its course, and yet preventing its progression to PBIE or the involvement of infectious agents. This review discusses the challenges presented by PBIE, latent infections, biofilms, fungal infections and the need to utilise diagnostic methods available and implement targeted treatments to optimise fertility in the mare.

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Mares were inseminated with motile spermatozoa suspended in 30-150 microliters Tyrode's medium directly onto the uterotubal papilla at the anterior tip of the uterine horn, ipsilateral to the ovary containing a dominant preovulatory follicle of > or = 35 mm in diameter, by means of a fine gamete intrafallopian transfer (GIFT) catheter passed through the working channel of a strobed light videoendoscope. Insemination of 10, 8, 25, 14, 11 and 10 mares with, respectively, 10.0, 5.0, 1.0, 0.5, 0.1 or 0.001 x 10(6) motile spermatozoa resulted in conception rates of, respectively, 60, 75, 64, 29, 22 and 10%. Deposition of 1.0 x 10(6) motile spermatozoa onto the uterotubal papilla began to approach the limit of successful fertilization. These doses are far lower than the 3-15 x 10(9) spermatozoa normally ejaculated by fertile stallions during mating, and the accepted minimum dose of 500 x 10(6) spermatozoa used for conventional uterine body insemination in mares. The simplicity of the technique offers a practical means of exploiting new breeding technologies that require very small numbers of spermatozoa in horse breeding.