Newborn foal "poisoned" by mother's colostrum
During the 2013-4 stud season one of our regular visiting mares "Red C" foaled normally a nice filly, but the foal collapsed and was found near death at around 36 hours of age.
We began emergency treatment immediately, but sadly the foal died after only a few minutes. Externally she appeared normal, but her mucous membranes (gums, conjunctiva) were very pale.
Post-mortem examination confirmed that the foal had died from a condition known as Neonatal Isoerythrolysis (NI) or more simply Neonatal Anaemia, where the actual cause of death is cellular oxygen deprivation from lack of intact red blood cells. The red blood cells normally carry oxygen from the lungs to all the tissues of the body, but in NI foals the red cells have been destroyed by antibodies produced by the mother and passed on to the foal via the colostrum.
It is completely normal - and essential for a healthy foal - that antibodies to all sorts of things are passed to the foal through colostrum, but where the NI problem begins is with (abnormal) production of antibodies specific to the foal's red blood cells.
The production of these "bad" antibodies is commonly instigated during a previous pregnancy - thought to be as a result of leakage of the foal's red cells through the placenta into the mare's circulation. The mare's immune system efficiently recognises the foal cells as foreign and creates the antibodies to deal with them in the future.
Recognition of the foal red cells as foreign by the mare comes about when the foal has a different blood type to the mare - one which it has inherited from the stallion. Blood types in horses are complex, with 8 major groups and over 30 variations within the groups. This makes it relatively difficult to predict whether a foal of a particular mare will have NI.
With Red C, the owner decided to put the mare back in foal but to a stallion from a totally different sire line to the sire of her NI foal - hoping to minimise the chances of a repeat occurrence.
As Red C approached birth in November 2014, 12 months after the death of her NI foal, we made preparations to test the new foal to ensure it was safe for him or her to drink the mare's colostrum.
The test involved taking a small sample of the newborn foal's blood and mixing it with colostrum from the mare serially diluted from 1:2 out to 1:64. The tubes of mixture were then centrifuged, and the red cells that had been spun to the bottom of the tube examined for agglutination. We were interested in the dilutions greater than 1:16 - if agglutination occurred in these tubes then our foal was definitely in line for NI if allowed to suckle.
A lovely healthy filly was born around 11pm, and samples of blood (foal) and colostrum (mare) taken immediately. Mare and foal were left together initially, as the foal would take some time to stand - time to get our test done before she started drinking the potentially lethal colostrum.
As the tubes were removed from the centrifuge, it was clear that agglutination of the cells had taken place even in the dilute colostrum samples. Smears examined under the microscope confirmed that the foal's red cells were clumping unnaturally - a result of attack by colostral antibodies.
We seperated the Red C from her new foal by a gate through the middle of the stable, and began feeding the foal with colostrum from our supply - frozen for the purpose on day 0 or 1 from other mares.
Red C's beautiful rich colostrum was milked out of her udder and discarded - it would have been deadly for any foal with the same blood type as our newborn filly, and was therefore not safe to keep.
Baby C drank happily from a bottle, and although the mare was a bit puzzled by the milking, the gate and the whole seperation thing she good-naturedly submitted.
At 36 hours of age we performed an IgG test on the foal to confirm that it had received enough (normal, safe) antibodies from its diet of thawed frozen borrowed colostrum. The test returned a reading of well over 800.
At this point we considered that the foal's gastrointestinal tract would have become impermeable to the antibodies in Red C's milk - this normally occurs as early as 6-12 hours of age which is why colostrum at that time is so vital.
Mother and daughter were allowed to begin a normal relationship, although the foal was monitored closely for another 72 hours for signs of red cell destruction or any other symptoms.
Although the outcome was good on this occasion, Red C's owner has decided to retire her as a broodmare because of the likelihood of other NI foals in the future. At least he has a beautiful filly who can replace her mum in the breeding arena after her probable career as a performance horse.