No luck so far in the search for a low-allergen horse

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Owners in search of a low-allergen horse may have their work cut out, the findings of fresh research in Sweden suggest.

Researchers tested horses from 10 breeds for the presence of a common allergen known to cause a reaction in 77 percent of horse-sensitized people.

All the breeds tested, including the American Curly Horse, produced the allergen. The wide variation in levels seen was between individual animals rather than the breeds.

However, one clear trend was noticeable. The allergen for which they tested, known as Equ c 4, tended to be produced in larger quantities by stallions when compared with mares and geldings.

Susanne Victor and her colleagues in the Uppsala University Hospital study set out to test Equ c 4 levels in the dander, saliva, and urine of horses.

Equ c 4 is one of five horse allergens listed in the database of the World Health Organization and International Union of Immunological Society. They are dubbed Equ c 1 to 4, and Equ c 6.

Equ c 4 belongs to a family of proteins known as latherins. It most likely acts as a wetting agent in sweat. Latherins are responsible for the frothy nature of horse sweat.

The researchers, writing in the journal Clinical and Experimental Allergy, describe horses as an important source of allergens. “But the distribution of horse allergens is poorly understood.”

Equ c 4 seems to be an important allergen, they note, affecting more than three-quarters of horse‐sensitized individuals.

A total of 170 horses (87 mares, 27 stallions and 56 geldings) were used for the study.

© International Curly Horse Organisation

The breeds represented were the American Curly Horse, the American Quarter horse, Gotland pony, Icelandic horse, North Swedish horse, Russian Bashkir horse, Shetland pony, Standardbred, Swedish Warmblood and Thoroughbred.

All study horses were registered with their respective breed society.

In all, 252 dander and 248 saliva samples were collected for analysis. Urine samples were taken from 21 of the horses.

Equ c 4 was present in all dander and saliva samples, the authors said. There was a great variation of levels both within breeds and between breeds.

Equ c 4 was found in 19 of the 21 urine samples.

“Adjusted for age, sex and changes over time, no differences between breeds could be seen in dander, while in saliva the North Swedish horse showed lower levels of Equ c 4 than any other breed.”

“The levels of Equ c 4 protein in dander and saliva were significantly higher in samples from stallions compared to mares and geldings, independent of breed,” they reported.

Discussing their findings, the authors say that, to their knowledge, their work represents the largest study of horse allergen profiles performed to date.

“We show that the horse allergen Equ c 4 is present in all dander and saliva samples from 10 different horse breeds.”

Its presence, they say, is understandable since Equ c 4 plays a role in the temperature control of equines.

“Likewise, the presence of the latherin protein Equc 4 in saliva helps wet the fibrous feed that horses eat.”

The authors note that horse dander, saliva and urine are all important allergen sources for people working in stables.

“However, for people allergic to horses, dander is more likely to be the most relevant source of the horse allergen Equ c 4, since dander is easily airborne.”

They concluded: “Our results suggest that none of the horse breeds studied here can be recommended for individuals allergic to Equ c 4.”

The study team comprised Victor, Anna Rask‐Andersen and Lena Elfman, all with the Department of Medical Sciences, Occupational and Environmental Medicine at Uppsala University Hospital; Erik Lampa, with the Uppsala Clinical Research Center at Uppsala University; and Jonas Binnmyr, with the Department of Clinical Neuroscience, Therapeutic Immune Design Unit, part of the Karolinska Institutet in Stockholm.

Levels of horse allergen Equ c 4 in dander and saliva from ten horse breeds
Susanne Victor, Jonas Binnmyr, Erik Lampa, Anna Rask‐Andersen, Lena Elfman
Clinical and Experimental Allergy, February 4, 2019, https://doi.org/10.1111/cea.13362

The study, published under a Creative Commons License, can be read here

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