A model to explain foaling
Keywords: equine, education, model, foaling
The author uses this model frequently, especially during the foaling season when students participate in foal watches and when owners require instructions on what to expect during foaling and when to intervene. The model can be used to demonstrate the diffuse nature of equine placentation and how readily this may detach from the endometrium in cases of dystocia; far more rapidly than in ruminants. They are informed that this (in large part) accounts for the high death rate in equine dystocia. It is emphasized that second stage foaling is also very rapid and that the foal is likely to die unless the first responder has basic knowledge of how to respond during foaling. This is why the teaching model has proven valuable and why the author encourages others to build similar models.
With an assistant holding the red velvet allantochorion stationary within an imaginary uterus, the author demonstrates how the allantochorion remains attached to the endometrium after it has ruptured at the site of the cervical star. At this point, the author usually digresses, showing how the allantochorion can become detached from the endometrium, even before it has ruptured at the cervical star. In that case, it would move caudally and appear at the vulva lips instead of the amnion. This serves to introduce the subject of premature placental separation (red bag) and the importance of rapid intervention should that occur.
Progressing in the vein of a normal foaling, the author shows how the amnion appears at the vulva lips with the forelimbs and muzzle of the foal visible through the amnionic membrane. The translucent polyester material used for the model allows this to be demonstrated clearly. There is an elasticized opening in the amnion. This opening shows where an attendant would cut the amnion or where it would rupture spontaneously. The author notes the possibility of asphyxiation in foals caused by an intact amnion remaining over the foal's muzzle after birth and consequently, stresses the need to transect or rupture the amnion when it first appears at the vulva lips.
At this time (before the simulated second stage is complete) the author may pull the model apart so that it is clear that the umbilical cord has two distinct parts; the intra-amnionic cord and the extra-amnionic cord. It is emphasized that this anatomy is distinctly different from that in ruminants where the amnion is attached to the chorion and there is no extra-amnionic cord. Furthermore, the author continues, it is that difference in anatomy that prevents the amnion from leaving the vulva lips and suffocating the newborn ruminant. In horses by contrast, the amnion is shown (in the model) to be free of the chorion, tethered to it only by the extra-amnionic cord. This allows the amnion to be born without rupturing, making neonatal asphyxiation a significant reality in horses; hence the need for amnionic rupture by the attendant.
At this time as well, for students of veterinary medicine or animal science it is useful to show a major difference in the anatomy of the intra- and extra-amnionic umbilical cords i.e. the presence or absence of the urachus. In the model, a yellow-colored string on the intra-amnionic umbilical cord represents the urachus. The urachus is shown to leave the umbilical cord where leaves the amnion and emerges into the allantois. This is used to demonstrate how allantoic fluid (predominantly urine) accumulates within the allantoic cavity. If the model is re-assembled at this point, it is possible to demonstrated how the allantoic fluid escapes when the allantochorion ruptures at the cervical star. The author adds that this is the first major discharge of fluid that occurs during foaling; before the rupture of the amnion and the discharge of amnionic fluid.
With the model re-assembled and the elasticized opening of the amnion at the vulva lips, the author emphasizes the need for immediate examination of fetal presentation, position and posture. Noting those conditions under which foaling is unlikely to proceed without specialized assistance (wry-neck, shoulder flexion, breech posture etc), the author turns to basic obstetrical mutations, especially carpal flexion and the need to repel the foal to obtain space for mutation. With the current model, the stuffed toy has short limbs that make it difficult to demonstrate malposture. A longer limbed toy would be preferable.
With the toy foal in normal position and posture, one can suggest to the student or owner that with a live foal, this is a time when one could contemplate leaving the stall, to observe the completion of foaling from a distance. Alternatively, if progress appears to have stalled, to intervene as necessary.
Once the toy foal has been "delivered", it is easy to demonstrate how the placenta can be expelled inside out or in its normal anatomical situation. The author usually takes this opportunity to mention that the placenta should be kept for inspection to ensure that placental fragments have not been retained and that there are no signs of placental pathology. This is also a convenient time to introduce the idea of time limits for placental expulsion and suckling (~3 hours in both cases).
Having used this model for many years, the author can attest to its value in teaching students and preparing horses owners for foaling.
