Insect bite hypersensitivity (IBH) is
a seasonal recurrent allergic reaction of horses to the
bites of certain
spp. and is found through-
out the world. The aim of our study was to estimate
the heritability and repeatability of IBH in the Dutch
Shetland pony population. A total of 7,924 IBH scores
on 6,073 mares were collected during foal inspections
in 2003, 2005, and 2006. Mares were scored for clinical
symptoms of IBH from June until February by 16 in-
spectors. Of all mares, 74.4% (n = 4,520) had a single
observation, 20.7% (n = 1,255) had 2 observations, and
4.9% (n = 298) had 3 observations in different years.
The overall mean IBH prevalence was 8.8%. Heritability
was 0.08 (SE = 0.02) on the observed binary scale and
0.24 (SE = 0.06) on the underlying continuous scale.
Repeatability was 0.30 (SE = 0.02) and indicates that
including repeated observations of the clinical symp-
toms of IBH will improve the accuracy of breeding val-
ues for IBH. We conclude that IBH, based on clinical
symptoms, is a heritable trait in the Dutch Shetland
pony population. Therefore, the IBH prevalence in this
population can be decreased by selection.
heritability, horse, insect bite hypersensitivity, repeatability
©2009 American Society of Animal Science. All rights reserved.
J. Anim. Sci. 2009. 87:484–490
Insect bite hypersensitivity (
) is a seasonal re-
current allergic reaction of horses to the bites of cer-
spp. (Riek, 1954). The allergic reaction
causes intense pruritus, which results in self-inflicted
trauma; open wounds and secondary infections may
follow. Therefore, the welfare of affected horses is seri-
ously reduced. The commercial value of affected horses
is also reduced because of disfiguration (Broström et
al., 1987; Fadok and Greiner, 1990). Due to extreme
discomfort, affected horses are often unsuitable for rid-
ing or showing purposes (Gortel, 1998). There is no
currently available effective treatment for or prevention
against IBH (Anderson et al., 1996; Friberg and Logas,
1999; Pilsworth and Knottenbelt, 2004).
The etiology of IBH is multifactorial in origin and in-
volves environmental and genetic factors (Lange, 2004;
Björnsdóttir et al., 2006; Grandinson et al., 2006).
Although warm- and cold-blooded horses of various
breeds worldwide are affected (Anderson et al., 1988;
Littlewood, 1998; Steinman et al., 2003), heritabilities
of IBH have been estimated only in small populations
of Icelandic horses (Unkel et al., 1987; Lange, 2004;
Grandinson et al., 2006). Therefore, no heritability es-
timates in breeds other than Icelandic horses are avail-
able in the scientific literature.