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HYPP in Quarter Horses
WRITTEN BY: RIRDC Equine Research News   [January 1995]

The problem of hyperkalemic periodic paralysis (HPP) was first reported in Quarterhorses in 1985 in the USA. The signs of the condition were intermittent muscle tremors and spasms and in some cases the horses became wobbly and even went down, unable to get up for a period of time. It was found that during these episodes the level of potassium in the blood rose greatly above normal. Subsequent work demonstrated that this was an inherited condition and that all known cases were descendants of a common sire. The particular stallion (Impressive) accounted for about 2% of all registered Quarterhorses in the USA. The current study examined show records of HPP affected and HPP unaffected horses to determine if HPP affected horses had a more successful show career.

The results showed that the HPP affected horses did significantly better in halter classes than did the unaffected horses. It appears that this may be because HPP affected horses have a more well muscled appearance and selection for this type of appearance by judges, inadvertently selects for the type of horses likely to be affected by HPP. At this stage HPP is uncommon in Australia, but the gene has been found in several hundred horses. It appears that all these horses trace back to the Impressive line.

Ref: JM Naylor Selection Of Quarter Horses Affected With Hyperkalemic Periodic Paralysis By Show Judges J. Am. Vet. Med. Assoc. Vol 204, No. 6, March 1994 pg. 926)

Reprinted from the RIRDC Equine Research News with the permission of the Rural Industries Research and Development Corporation.

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