Isoerythrolysis

When Pool House Equine Clinic vet Jonathon Withers was called to a sick 4 day old foal he immediately recognised that it urgently required a blood transfusion. It was very dull, sleepy, depressed and had stopped feeding.

Clinical examination revealed a heart rate of over 140 bpm, rapid breathing, bright yellow gums and conjunctiva (icterus). Blood tests confirmed that the percentage of red blood cells in circulation had fallen to 11% (usually nearer 40% in foals). The red cells are vital in that they take oxygen to the body tissues from the lungs. Without an adequate number of red cells the muscles and other organs become deprived of oxygen and the affected animal becomes tired and weak. Unchecked this can prove fatal.

These signs are typical of a fatal foal disease known as neonatal isoerythrolysis. This is caused by antibodies absorbed from the mare (in colostrum) attacking the foal’s red blood cells and destroying them. In other words the foal is a different blood group to it’s mother. The ‘Rhesus baby’ syndrome in humans is a very similar illness. Usually it only occurs when mares have had a foal previously.

The foal was rushed into Pool House Equine Clinic for a life saving blood transfusion. There is no equivalent of the ‘blood transfusion service’ for horses so a donor horse had to be found quickly. An unrelated gelding is usually the best candidate and that is where Blue Cross horse Harold stepped in. Harold is a permanent resident at the Clinic where he is ridden occasionally and spends the rest of his time as a companion horse to some of the clinic’s patients. Three litres of blood were required which is a relatively large volume. A small amount of local anaesthetic was injected over Harold’s jugular vein and the blood was collected into special plastic bags containing anticoagulant. This took almost an hour and Harold stood patiently throughout not even needing any sedation.

The blood was collected in half litre bags and as each was filled it was immediately transfused into the foal by equine vet Renske van der Rijt, she commented that the effect of the transfusion was like a miracle, ‘the foal went from collapsed and lethargic to lively and energetic during the course of the transfusion – so much so that by the end of the procedure we had to sedate him to keep him still!’ Blood tests after the transfusion confirmed that the red cell percentage had doubled to 24% – a safe level.

Harold’s carer Rolleston Centre Vet Richard Stephenson said that, ‘without Harold we would certainly have lost the foal. It was almost as if he knew he was being helpful. Normally he can be a bit stroppy but he stood perfectly for over an hour to let us get the necessary blood. He has had some extra feeds as a reward – but we have to be very careful that he doesn’t put on too much weight!’

The foal was closely monitored over the next 10 days. Repeated blood test showed a stable red cell count. The foal went on to make a full and uneventful recovery.

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