How to Monitor the Subfertile Mare During the Last Trimester

After expending considerable time in establishing pregnancy in the subfertile mare, it is imperative that she be adequately monitored to detect complications in the later part of gestation. The most likely complication to arise during the last third of gestation in the subfertile mare would be placentitis. Timely identification of placentitis is crucial for multimodal therapy to be successful. Other potential reproductive causes of high-risk pregnancy such as utero growth retardation and cord abnormalities might also be identified. Placentitis has been reported to be responsible for 9.8%, 19.4%, 24.7%, and 33.5% of abortions, stillbirths, and perinatal losses in horses. Bacterial infections are responsible for 53% of these losses; Streptococcus equi subsp. zooepidemicus (S. zooepidemicus) was isolated in 28% of these cases. Other bacteria frequently identified were Escherichia coli, Leptospira spp., Crossiella equi, Pseudomonas spp., S. equisimilis, Enterobacter spp., Klebsiella spp., -hemolytic streptococci, Staphylococcus spp., and Actinobacillus spp. Infection was localized to the cervical star in 95% of cases, supporting the argument that ascension of aerobic bacteria through the vagina and cervix is the most frequent route of infection. Clinical signs include vulvar discharge, udder development, prenatal lactation, and premature delivery or stillbirth. Abortions can occur from 75 days to term, although the majority of clinical cases are presented to practitioners during the third trimester. In a survey of 200 fetal membranes with infective placentitis, 36% of those with bacterial infections were recorded to have had premonitory signs, compared with 63% of those with fungal infections. A notable exception to the transcervical ascension of pathogens is focal mucoid placentitis (“nocardioform placentitis”) caused by actinomycetes. The majority of isolates have been C. equi, although other species have been identified, including Amycolatopsis spp., Streptomyces spp., and Cellulosimicrobium cellulans. Although sporadic cases of nocardioform placentitis have been reported in South Africa, Florida, and Italy, most reported cases are from Kentucky. Inflammation of the chorion extends from the cranial ventral uterine body, usually at the base of the gravid horn, with an adherent tan to brown exudate. Precocious udder development is occasionally observed with nocardioform placentitis, but vaginal discharge is uncommon. The majority of abortions occur during the 9th and 10th months of gestation. Interestingly, other non-nocardioform bacteria have been isolated