Animal Reproduction Science 64 2000 49–64
A survey of the fertility of Icelandic stallions
M.C.G. Davies Morel
∗
, V. Gunnarsson
1
University of Wales, Welsh Institute of Rural Studies, Aberystwyth, Ceredigion SY24 5DP, UK Received 15 December 1999; received in revised form 23 March 2000; accepted 18 July 2000
Abstract
Very limited information is available on the breeding performance of Icelandic stallions, let alone the effect that management practices may have had on such performance. As an extensively
kept, largely genetically isolated breed of horse it provides a good model for the study of factors that affect reproductive performance without the additional complication of selective breeding,
infectious infertility and breed effect. A survey was conducted using 27 Icelandic stallions covering 1590 mares within the normal Icelandic breeding system May to September. During the season,
stallions cover mares within three periods of time, each period being of a similar length average 35.5 days. During period 1, mares are covered in hand and at pasture. During periods 2 and 3, all
mares are covered at pasture. The overall fertility rate for Icelandic stallions was calculated. The effect of a range of variables on fertility was investigated statistically using a number of models in an
attempt to minimise the effect of confounding factors. An overall adjusted fertility rate for Icelandic stallions of 67.7 was obtained. The following factors were shown to have a significant effect on
fertility: age of mare P 0.001, training level of stallion P 0.05 and method of breeding P 0.05. For some individual stallions reproductive status of the mare also had a significant
P 0.001 effect. Many of these factors have been observed to effect FR in other more intensively managed equine populations. However, the less dramatic detrimental effect of age and the lack of a
significant effect of mare reproductive status in most stallions suggests that infertility problems are less evident in Icelandic mares, possibly due to less emphasis on selection for athletic performance
and the accepted culling of subfertile stock. © 2000 Elsevier Science B.V. All rights reserved.
Keywords: Horse; Fertility; Breeding
1. Introduction
The Icelandic horse was introduced into Iceland, mainly from Norway, 9–11 centuries ago. It has subsequently remained largely purebred Eldjarn, 1981; Adalsteinsson and
∗
Corresponding author. Tel.: +44-1970-624471; fax: +44-1970-611264. E-mail address: midaber.ac.uk M.C.G. Davies Morel.
1
Present address: Holar College, 551 Saudarkrokur, Iceland. 0378-432000 – see front matter © 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 8 - 4 3 2 0 0 0 0 0 1 9 2 - 5
50 M.C.G. Davies Morel, V. Gunnarsson Animal Reproduction Science 64 2000 49–64
Thorkelsson, 1991; Palsson, 1996. The Icelandic horse stands 135 cm high with an es- timated worldwide population of 160,000 80,000 within Iceland. The horses are largely
managed extensively, stallions running out with their groups of mares under semi feral con- ditions during the summer. Some horses which are in training are kept in during the winter
period and some of the more popular stallions cover mares in an in-hand mating system at the beginning of the season, before being turned out to pasture with mares. The breeding
season of the Icelandic horse is from May to September with a peak from May to July Dyrmundsson, 1994. Very limited information is available on the breeding performance
of the Icelandic horse, let alone the effect that management practices may have. One re- port, however, suggests that fertility rates may be as high as 82.1 Hugason et al., 1985,
which compared to the fertility rates reported for other equine populations, for example, Thoroughbred 53–77 Sullivan et al., 1975; Merkt et al., 1979; Bowen, 1990; McDowell
et al., 1992, Ponies 35–82 Day, 1939; Hugason et al., 1985; Bristol, 1987; Garrot and Taylor, 1990, Heavy horses 59 Day, 1939 and Light horses 52 Day, 1939 is very
good. However, this figure arose from work carried out on a limited number of mares, and the results appear to exclude barren mares in some instances, hence, suggesting a possible
over estimation of fertility Hugason et al., 1985.
An official registration system for Icelandic horses has been in operation for many years but is limited in the information it records regarding reproductive performance. The fer-
tility of Icelandic stallions, though believed to be high, is felt by many breeders to have declined in recent years with a greater incidence of subfertile stallions. This survey, there-
fore, specifically aims to provide an overall figure for the fertility of Icelandic stallions. It is also hoped to provide information on the effect that various parameters may have on fertility
rates. Only with such basic information is it possible to analyse the current fertility rates of Icelandic horses and to organise breeding management in a way best suited to maintaining
good fertility. Such information will also create a starting point for further research and development work in the field. More generally this research, on an unimproved, genetically
isolated group of ponies, rather than the more usually used horses, may also help eluci- date some of the differences that exist between horses and ponies; the differing effects of
environment and the effects of man’s intensive management and selective breeding.
2. Materials and methods
