Neonatal Isoerythrolysis
Neonatal
isoerythrolysis is a condition in which the mare creates antibodies against
the foal’s red blood cells, and then passes these antibodies to the foal via
the colostrum. Once the foal absorbs
these antibodies, they result in lysis of the foal’s red blood cells within
24 - 36 hours after birth. This red blood cell destruction is
widespread throughout the foal’s body and can lead to life-threatening anemia
and/or jaundice. (This is similar to
the human Rhesus factor where a woman that is Rh-negative gives birth to her
second or subsequent child that is Rh-positive, resulting in destruction of the
newborn’s red blood cells). The mare
must have had previous exposure to blood that contained these particular
antibodies to the foal’s blood (such as through a blood transfusion or a
previous foaling) in order for this situation to occur.
Signs of
neonatal isoerythrolysis depend upon the rate and severity of red blood cell
destruction. Affected foals are born
healthy, and then typically develop signs within 24 – 36 hours (as stated
above). In severe cases, the signs of
NI may be evident within 12 – 24 hours.
Whereas, in mild cases, signs may not be present until
3 – 4 days of age. NI foals will develop progressive anemia,
thus leading to depression, anorexia, collapse, and death. These foals may also develop pale mucous
membranes that later become yellow, or jaundiced.
If neonatal isoerythrolysis
is suspected in a foal that is less than 24 hours old, further ingestion of the
mare’s colostrum must be prohibited.
This foal should be seen by a veterinarian and fed an alternative source
of colostrum via a nasogastric tube.
Foals that are over 24 hours old when suspected to be suffering from
neonatal isoerythrolysis need to be seen by a veterinarian immediately for
evaluation and treatment. These foals
may need to undergo a blood transfusion in order to save their life.
Prevention of neonatal
isoerythrolysis is more effective than treatment. Prevention begins with identifying mares at risk for producing a
foal with NI. These are mares that have
previously had an NI foal or are positive for antibodies to the Aa and/or Qa
blood antigens. (A veterinarian will
need to draw a blood sample from the mare in order to detect the presence of
these blood antigens). Two common
breeds that express an increased incidence of NI are Standardbreds and
Thoroughbreds. Individuals who are
involved with the breeding of these horses should be particularly aware of this
life-threatening condition.
Colostrum from
any NI-producing mare should never be used or saved. Alternative sources of colostrum should be
acquired prior to parturition for cases where an NI foal is highly likely.
The National Colostrum Network was founded at the
University of Minnesota-College of Veterinary Medicine.