Perinatal Asphyxia in Foals
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As the
foaling season begins, veterinarians and farm managers have to deal
with problems related to delivery of foals. Among these is a condition
called perinatal or neonatal asphyxia.
Asphyxia is defined as a decrease in the amount of oxygen supplied
to the tissues as a result of a reduction in the amount of oxygen
in the blood or the amount of blood flowing to the tissues. Perinatal
asphyxia is a syndrome caused by decreased oxygenation of the foal’s
tissues during the birth process.
Foals
may appear normal at birth only to develop clinical signs 6 to 24
hours later; they may be abnormal at birth; or they may be stillborn.
Foals
with perinatal asphyxia exhibit an array of clinical signs referable
to the central nervous system (CNS) but diarrhea, colic, and decreased
urine output may occur. Commonly observed CNS signs include jerky
movements, spasms, diminished sucking reflex, wandering, blindness,
seizures, and coma.
Causes
of perinatal asphyxia include placental abnormalities, dystocia
or delayed delivery, twinning, congenital malformations, and maternal
illness. Treatment involves good nursing to address the multisystemic
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 Livestock Disease Diagnostic Center,
163 cases of perinatal asphyxia were diagnosed over a 3-year period
(1998-2000), which represented approximately 7% of all fetuses 10-11
months of gestation and 1 day of age (Table 1).
A
review of cases where sex was indicated revealed that 69% were males
and 31% females with many different breeds represented. A diagnosis
was made only in foals after 300 days of gestation with no foals
(fetuses) younger than 300 days gestation. 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 is the result of excessive squeezing of the foal as it
passes through the birth canal suggesting a difficult or delayed
delivery. Cases of perinatal asphyxia are consistently negative
for infectious agents.
The
fact that 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 condition should be treated. 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.
CONTACT:
Dr. Neil M. Williams, (859) 253-0571, nmwillia@ca.uky.edu
Livestock Disease Diagnostic Center
