Lavender Foal Syndrome

Lavender Foal Syndrome (LFS), also called Coat Color Dilution Lethal is a genetic disease that affects newborn foals of Arabian horse bloodlines. Cases reported in peer-reviewed veterinary literature are entirely of foals descended from a number of "Egyptian" or Egyptian-related bloodline groups. However, there is a small amount of ancedotal evidence that suggests LFS may occur in Arabian horses of other bloodlines. The condition has been recognized since mid- to late- 1950s.^[1]

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The condition gets its name because most, though not all, affected foals are born with a unique coat color dilution that lightens the tips of the coat hairs, or even the entire hair shaft. The color has variously been described as a silver sheen, a dull lavender, a pale, dull pinkish-gray or pale chestnut.^[2] This dilution differs from gray foals because grays are born a dark color and lighten with age. It is also different from roan, because the hair is of a uniform shade, not of intermingled light and dark hairs.

Foals with LFS are unable to stand, and sometimes cannot even attain sternal recumbency (to roll from their side to lie upright, resting on the sternum, a precursor position to standing). They may lay with their necks arched back, make make paddling motions with their legs, and often have seizures. They are usually euthanized within a few days of birth. There is currently no genetic test for LFS and there is no cure.^[3] In some cases, the mare may also have difficulty foaling, though foaling difficulties are not the cause of the condition.^[4]

Lavender foal syndrome is most commonly thought to be created by a recessive gene.^[4] When a horse is heterozygous for the gene, it is a carrier, but perfectly healthy and has no symptoms at all. If two carriers are bred together, however, classic Mendelian genetics indicate that there is a 25% chance of any given mating producing a foal that is homozygous for the gene, and hence affected by the disease. It is theorized, though not yet tested, that LFS may also be somehow linked to another genetic disease that affects Egyptian-related Arabians, juvenile epilepsy. This theory has been raised because of a small number of horses who have produced both LFS and epileptic foals.^[4]

LFS is one of six genetic diseases known to affect horses of Arabian bloodlines.^[2] There are genetic diseases that affect other horse breeds,^[5] including different coat dilution lethals, such as lethal white syndrome. In addition, the color white in horses, when created by the "dominant white" (W) gene, is fatal if homozygous.

Research into the genetics of LFS has been conducted at the University of California, Davis and Cornell University in the United States, and the University of Queensland in Australia. Lavender foal syndrome should be considered in any weak newborn Arabian or part-Arabian foal with some degree of "Egyptian" breeding if the foal has trouble standing, if other signs of neurological problems are present, and especially if they have a light coat coloring.^[1]

References

Additional information

• Page P, Parker R, Harper C, Guthrie A, Neser J. "Clinical, clinicopathologic, postmortem examination findings and familial history of 3 Arabians with lavender foal syndrome." J Vet Intern Med. 2006 Nov-Dec;20(6):1491-4. Department of Companion Animal Clinical Studies Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa. PMID: 17186871