OLWS (Overo Lethal White Syndrome, EDNRB)
Hereditary malformation of the intestinal nervous system in foals born pure white to spotted parents. The cause is a variant in the EDNRB gene: heterozygous carriers are completely healthy and show the frame overo pattern, while homozygous foals have no functioning intestinal nerve cells and cannot move the gut contents along. The trait is unambiguously identifiable by gene test — which makes the case entirely avoidable.
Veterinary care required
This condition belongs in veterinary diagnosis and treatment. Compounds are at most supportive.
Priority · vet & management
A white-born foal from a spotted mating belongs in veterinary hands immediately. There is no treatment for the malformation; the veterinary decision serves to spare suffering. The real lever lies before the mating: the gene test is unambiguous and inexpensive.
Possible causes
- · autosomal-recessive variant in the EDNRB gene
- · both parents are carriers (frame overo pattern)
- · carriers themselves are healthy and fully viable
- · the frame pattern can be very subtle and missed without a gene test
Supportive compounds · supplementary feed, not medication
Prevention
Test both parents for EDNRB before mating. Two carriers must not be mated with each other — carrier x non-carrier is unproblematic and preserves the frame pattern in breeding.
Equiterna's take
Equiterna treats OLWS as a pure breeding question: the gene test comes before every mating, and carrier status is no blemish on the individual animal. Whoever breeds frame overo breeds with the trait — deliberately and by plan.
Usage note
This content is for information and education. It does not replace veterinary diagnosis or treatment. If your horse shows signs of illness, consult a veterinarian.
Equiterna is an intermediary platform for equine knowledge, marketplace and tools — not a veterinary-medicines dealer, veterinary practice or pharmacy. Compound information is study-attributed and free of healing claims. Legal framework: Regulation (EU) 2019/6 / TAMG (DE/AT), Feed Regulation (EC) 767/2009, FEI Prohibited Substances List, HWG.