Delivery Problems Cause Perinatal Asphyxia

Perinatal or neonatal asphyxia is a syndrome caused by decreased oxygenation of a foal's tissues during the birth process, writes Dr. Neil Williams in the January edition of Equine Disease Quarterly, which is published by the University of Kentucky.

Foals with perinatal asphyxia exhibit an array of clinical signs referable to the central nervous system, but diarrhea, colic, and decreased urine output may occur. Some foals are stillborn or are abnormal at birth, but in others, clinical signs do not develop until six to 24 hours after birth.

Causes of perinatal asphyxia include placental abnormalities, dystocia or delayed delivery, twinning, congenital malformations, and maternal illness. Treatment involves good nursing to address the multi-systemic nature of the condition designed to correct hypoxia, depression, decreased ventilation, hypovolemia, decreased cardiac output, seizures, sepsis, and gastric ulceration.

At the University of Kentucky's Livestock Disease Diagnostic Center, 163 cases of perinatal asphyxia were diagnosed over a three-year period (1998-2000). The total represented approximately 7% of a group made up of all fetuses presented to the diagnostic center that had a gestational age of 10-11 months and all foals that were one day old.

A review of cases where sex was indicated revealed that 69% were males and 31% were female. Many different breeds were represented. Case histories often mentioned dystocia. However, there were many cases in which it was stated that foaling was normal.

Histories sometimes indicated that the placental membranes were improperly delivered or visualized before the foal was observed. In most cases, the foal was dead on delivery. However, some were born alive, but had weak vital signs and died. Examination did not reveal any one lesion that allowed the diagnosis to be made.

Typical findings at necropsy included partially aerated lungs, petechial hemorrhages in the mucosa of the respiratory tract and on the heart, edema in the mesentery and mesenteric lymph nodes, and hemorrhage into the shoulder joints with reddish staining of the articular cartilage.

The hemorrhage was the result of excessive squeezing of the foal as it passed through the birth canal, suggesting a difficult or delayed delivery. Cases of perinatal asphyxia were consistently negative for infectious agents.

The fact the placenta is passed so quickly after delivery indicates it must begin detaching from the uterus during or soon after delivery. The foal must be delivered quickly or it risks oxygen deprivation. The potential for injury is great considering the relative size of some foals and the strength of mare contractions.

Pregnant mares should be maintained in good body condition and any illness or other problem should be treated. Farm managers can prevent perinatal asphyxia by monitoring mares for signs of impending parturition and being in attendance for all foalings. Assistance should be given during the delivery process to ensure the foal does not spend excessive time in the birth canal.

If dystocia is encountered, it should be dealt with quickly and veterinary assistance sought if indicated. Foals showing signs of asphyxia should be examined immediately by a veterinarian and appropriate therapy initiated.