LORI.equine

Hydrops

Keywords: hydrops, equine, foaling, induction

A 17-year-old Standardbred mare was presented for signs of abdominal discomfort, anorexia and a possible ventral rupture (erroneously referred to as "rupture of the pre-pubic tendon"; see this LORI entry). This mare was due to foal approximately 2 weeks after the time of presentation. The referring veterinarian reported rapid abdominal enlargement over the two week period before presentation.

The uterus was distended with fluid and a live fetus could be detected by ballottement per rectum. In a single day after admission, this mare gained 10 kg in weight, strongly suggesting some form of hydrops.

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In the image, abdominal enlargement and ventral edema is indicated by a red arrow. Because of the potential for ventral rupture, foaling was introduced using oxytocin.  Milk electrolyte changes were used to determine the optimal time for induction. At the onset of second stage, it was noted that the chorioallantois was abnormally thickened. It was transected and a small, live filly foal was delivered in caudal presentation.

It was estimated that approximately 100 L of fluid had been released when the placenta was transected. The mare weighed 710 kg on admission and 570 kg immediately after foaling. The placental weight was 15 kg (approximately double its normal weight) and her foal weighed 30 kg. Therefore, the fluid content of the placenta was 90 kg or 90 liters. The normal amount of allantoic fluid normally varies from 8 to 15 L1 and the amnionic fluid somewhat less. Therefore there was little doubt that this mare had experienced hydrops allantois. However, the possibility of additional hydrops amnion component could not be excluded.

Shortly after foaling the mare experienced severe hypovolemic shock requiring aggressive fluid therapy. Due to continuing pain and damage of ventral abdominal structures that would probably compromise future pregnancies, the mare was euthanized at the request of the owner.

Notes: Both hydrops allantois and hydrops amnion are rare in mares. Although one is said to be more common that the other, neither can be dismissed on rates of probability when a mare is presented. Also, these condition are so sporadic that their etiology has not been properly studied.  Hydrops of either type can be diagnosed by sudden changes in weight, girth size and the ultrasonographic appearance of fetal fluids. Also, the biochemistry of the fetal fluids can be used to differentiate between hydrops in either compartment.

A major challenge in the case management of hydrops is to stabilize the mare after large amounts of fluids have been lost from the abdomen. Although this fluid is not lost from the blood stream, this author suggests that the sudden decrease in abdominal pressure may cause pooling of blood in the abdominal vessels, vascular dilation and following laplace's law, fluid loss into the peritoneal cavity

 References:

Arthur, C.H. 1975. Veterinary reproduction and obstetrics.  Fourth edition, London, Balliere Tindall. 41-42

Blanchard, T.L. et al. 1987. Hydroallantois in two mares. Equine Vet J. 222-225

Christensen, B.W. et al. 2006. Management of hydrops amnion in a mare resulting in birth of a live foal. J. Am. Vet. Med.Assoc.228:1228–1233

Honnas, C.M. et al 1988. Hydramnios causing uterine rupture in a mare. J.Am.Vet.Med.Assoc. 193:334-336