Transrectal ultrasonography and plasma progestin profiles identifies feto-placental compromise in mares with experimentally induced placentitis.

The research examined the effectiveness of using transrectal ultrasonography and progestin profiles to identify complications in the fetus-placenta connection in mare pregnancies involving conditions simulating placentitis, a bacterial infection of the placenta often leading to premature foaling.

Experimental Design

• The design included 22 pregnant mares grouped into different categories: Control mares, instrumented controls, instrumented inoculated mares and inoculated mares.
• The last two groups of mares were injected with Streptococcus equi subsp. zooepidemicus, an infectious bacterial pathogen known to affect horses, to simulate a condition of placentitis.

Data Collection and Monitoring

• The research involved regular weekly examination of the mares, including assessment of progestin levels in the blood (a group of hormones involved in the pregnancy process), assessment for signs of vulvar discharge, and monitoring of development in the mammary gland as well as other physiological parameters.
• Data regarding the thickness of the uterus and placenta (CTUP), and any signs of placental separation were also collected, either daily or several times a week.

Diagnostic Methodology

• The levels of progestins in the plasma were plotted in a profile and patterns in the data were identified, allowing for the detection of abnormalities.
• An ‘abbreviated profile’ was derived using four samples of progestin collected at 48-hour intervals. If the samples showed a rise or fall of more than 50% compared to the first sample, it was classified as abnormal.
• Any measure of CTUP greater than 1.0 cm or indications of placental separation were also labelled as abnormal.
• Finally, histology of the fetal membranes were conducted to confirm the condition of placentitis.

Results and Findings

• All mares in the inoculated groups developed placentitis and gave birth prematurely, whereas the control mares had normal pregnancies.
• Among the foals born, only one from the control group died due to delivery complications (dystocia), while none of the foals from the inoculated groups survived.
• All mares in the inoculated groups demonstrated abnormal progestin profiles as well as abnormal CTUP.
• Using the combined tests, 20 out of 22 mares were correctly diagnosed regarding their pregnancy outcomes.
• Notably, however, three of the inoculated mares showed minimal clinical signs and hence would have likely been overlooked in regular clinical settings.

Conclusion

In conclusion, the progestin profile examination, alongside transrectal ultrasonographic evaluations, were shown to be valuable in identifying compromised feto-placental conditions in the study mares. Despite some limitations (e.g. minimal symptomatic mares being overlooked), this diagnostic combination demonstrated strong potential for wider clinical application.