Íslenskar landbúnaðarrannsóknir - 01.03.1979, Blaðsíða 83

ÍSL. LANDBÚN.
j. agr. res. icel. 1979 11, 1-2: 81-93
Studies on traits in
the Icelandic toelter horses
I. Estimation of some environmental
effects and genetic parameters
PORVALDUR ÁRNASON
ABSTRACT
An analysis was undertaken on the effect of some environmental and genetic factors on four body
measurements and ten subjectively scored traits in Icelandic toelter horses. Of the environmental effects
inciuded in the model year of measurement turned out to have the most marked influence, but district of
origin was the least important. The effect of sex and age were significant in many instances. The body
measurements were found to be highly heritable and also highly mutually correlated both genetically and
phenotypically, but much less correlated with the subjectively scored traits. The ten traits, which can be
classified into three estimates ofbody conformation, four gaits, temperament, character and elegance under
the rider, had heritability estimates ranging from 0.12 to 0.22, with the execption of ,,pace“ which was
estimated to have heritability of the order of 0.50. No two traits were negatively correlated phenotypically.
The majority of the genetic correlations were positive and some quite high, but negative estimates were also
obtained.
INTRODUCTION
The breeding history of the Icelandic to-
elter horses (ponies) is to a great extent
unknown until 1900. As far as known they
were imported from Norway and possibly
Britain, by the settlers 11 centuries ago
(Bjarnason, 1956a; Bjarnason, 1974).
In the year 1901 breeders officially
started an attempt to improve the confor-
mation and performance of their ponies by
selection within the population. Until
1950 the breeding aim was a dual purpose
pony which was suited both to riding and
draught. In 1951 the present breeding
goal was declared and may be defined in a
6
broad sense as breeding of riding horses
both for domestic use and for export (JÓS-
afatsson, 1955; Bjarnason, 1956b).
Methods of objective quantitative me-
asurements of most of the characters sel-
ected for, have not yet been made avail-
able. In order to circumvent that problem
a scoring point index was developed and is
used at annual horse shows, where the
breeding stock is judged on conformation
and performance tested. The scoring in-
dex is composed often traits, which can be
classified into three estimates of body
conformation and seven performance