Little is known about the composition and physiology of fetal fluids in all domestic mammals in comparison with humans, where the amniotic fluid has been the focus of numerous reports. Previously, in the horse, there have been concerns regarding the safety of fetal fluid sampling and the risks to the well-being of the fetus and techniques limitations that may preclude serial assessment. The objective of this report was to describe a transabdominal ultrasound-guided technique to safely perform multiple fetal fluid collections during the last trimester of gestation in mares. Similar methodology has been described previously; however, here we described step by step how to perform fetal fluid sampling. Several illustrative images have been included to facilitate the understanding of the technique by others lacking experiences with the procedures. In addition, small modifications on the sedation protocols and sampling have been performed in the present study. Six light horse mares carrying normal singleton pregnancies (260-280days of gestation) were sampled three times at 5- to 7-day intervals (i.e., 0, 5, and 12 days). There were no apparent complications using the protocol described here. All mares delivered normal foals uneventfully. We foresee that the publication of this report may be useful to other research laboratories interested in studying the fetal fluids in mares, as well as in specific clinical evaluations of fetal well-being in research mares.
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