Genetic analysis of insect bite hypersensitivity (summer eczema) in Icelandic horses

Abstract

There is a lack of knowledge about the genetic background of eczema due to insect bite hypersensitivity, also called summer eczema, in horses. The condition is known in several horse breeds and countries and it causes reduced welfare of the horse and economic losses to the owner. The aim of this study was to estimate genetic parameters for summer eczema in Swedishborn Icelandic horses. A questionnaire was sent to owners of horses sired by stallions with more than 50 offspring born in Sweden between 1991 and 2001. Variance components of summer eczema classified as healthy, mild, moderate or severe were estimated using the threshold methodology with sire models. In addition, summer eczema was analysed as a binary trait (healthy v. affected). The analyses included 1250 horses sired by 33 stallions. The prevalence of summer eczema was 8%, with a range of 0% to 30% in different paternal half-sib groups. Offspring of dams suffering from eczema had a higher risk of developing eczema. The heritability for severity of summer eczema was estimated at 0.3 (s.d. , 0.2) with a threshold sire model. In contrast to the age of the horse, different geographic areas and gender were significantly associated with severity of the eczema. We conclude that genetic selection could decrease the prevalence of summer eczema among Swedish-born Icelandic horses. The amount and quality of data are, however, crucial for the possibility to introduce a genetic evaluation of summer eczema. The symptoms should be classified in several classes according to severity, and this classification could be made by the horse owner.

Genetics of equine insect bite hypersensitivity and genetic diversity in horses

“…That leads to clinical symptoms such as scratches on the skin surface, hair loss, lesions, and possibly secondary infections. The clinical symptoms appear mainly around mane and tail, but also in other areas of body (Peeters et al, 2014;Eriksson et al, 2008). Most horses typically show clinical symptoms around spring and summer (Schurink et al, 2013a) when Culicoides species are active.…”

“…Icelandic horses exported from Iceland to the European continent had IBH prevalence of more than 50% as reviewed in Schaffartzik et al (2012). The estimated prevalence of IBH in Swedish-born Icelandic horses ranged from 6.7% (441 horses used, (Brostrom et al, 1987)) to 8% (1,250 horses used, (Eriksson et al, 2008)). Knowledge regarding IBH prevalence in Exmoor pony population is limited.…”

“…Multiple genes seem to influence the genetic predisposition. Heritability of IBH on the continuous scale was estimated in Dutch Friesian breeding mares (0.16, SE = 0.06) (Schurink et al, 2011), Dutch Shetland breeding mares (0.24, SE = 0.06) (Schurink et al, 2009), Swedish-born Icelandic horses (0.30, SE < 0.20) (Eriksson et al, 2008), and Belgian warmblood horses (0.65 for clinical status) (Peeters et al, 2015).…”

“…It is important to investigate an effect of the environmental factors while estimating true genetic component influencing IBH susceptibility in horses. The environmental factors related to exposure to allergens like region of habitat of horses (exposure to allergens) (Eriksson et al, 2008;Brostrom et al, 1987), time period of collection of data (Schurink et al, 2013b), protective rugs (Olsen et al, 2011) have been observed to influence IBH prevalence. The environmental factors related to mares such as age, coat colour, wither height, body condition (amount of fat stored in the body) (Peeters et al, 2014;Schurink et al, 2013b) had significant effect on IBH prevalence.…”

“…The environmental factors related to mares such as age, coat colour, wither height, body condition (amount of fat stored in the body) (Peeters et al, 2014;Schurink et al, 2013b) had significant effect on IBH prevalence. The effect of sex in development of IBH susceptibility is inconclusive (Peeters et al, 2011;Eriksson et al, 2008;Brostrom et al, 1987).…”