Norwegian Fjord horse. Photo: Ingvild Rydjord Hansen

The available information regarding known origin and the kinship of the different Nordic native breeds is variable, but it appears that several breeds have similar descent (Table 6). For instance, genomic research found that the Finnhorse is closely related to Scandinavian horses (e.g. North Swedish horse, Icelandic horse), the Estonian horse, Mezen horse, Yakutian horse and Mongolian horse. Evidence of  genetic relationships between all the native Norwegian horse breeds and Mongolian horses have also been presented. It has also been shown that the Fjord horse is more closely related to the European wild horse (Tarpan) than the Asiatic wild horse (Przewalski) by looking at the number of chromosomes; the Przewalski horse has 66, while the Fjord and Tarpan horse have 64 chromosomes. Similarly, it appears that the Gotland pony is a descendant of the European wild horse Tarpan as well. Further, it is thought that the Icelandic horse is most closely related to the Nordland/ Lyngen horse across all breeds. The Icelandic horse is also related to the Fjord horse, the Faroese horse, and the Shetland pony. Studies have further revealed links between the Icelandic horse and Mongolian horse, which could reflect its relation to the Norwegian horse breeds. A recent whole-genome investigation of the Faroese horse found that they are closely related to other North Atlantic breeds, such as the Shetland pony and the Icelandic horse. Information regarding descent of the Danish and Swedish horse breeds is more limited. However, the North Swedish horse is believed to have similar descent to the Norwegian Dole breed, while the Swedish Coldblooded trotter descends from the North Swedish horse, suggesting that these breeds also could be related to Mongolian horses. Further, the Swedish Ardennes descends from the Ardennes in Belgium which are thought to descended from the Solutré horse. The Jutland horse share relatives with the Shire and Suffolk breeds, as the stallion Oppenheim (a mix of the breeds) is the ancestor of an important family that sired most of the Jutland population today. Furthermore, the Frederiksborg horse is a founder of the Knabstrupper.   

Several of these breeds are spread out globally and kept in different countries. For example, the Fjord horse and the Icelandic horse are very popular outside of their country of origin. Transboundary breeding could lead to changes in the expression or proliferation of genes to adapt to their environments long term (e.g., heat or sparse vegetation). In theory, this could contribute to spatial genetic diversity within the breed, but it also poses the question to whether environmental factors should be considered during decision-making regarding breeding and conservation plans. Registration and breeding legislation for the different breeds that reside in other countries would be useful to allow deeper knowledge about the breed populations and their spread.  The Icelandic horse has the database and studbook of origin, WorldFengur, that registers the pedigree and information about Icelandic horses worldwide. This is a good example of a good solution for a transboundary breed. 

Maintaining a high genetic diversity both within and between breeds, is important to ensure sustainable livelihoods of all species, including the horse. Genetic diversity is important for the overall adaptability of an organism. It is important in various sectors, including conservation biology, as high genetic diversity within a population provides individuals with a better predisposition for tolerating stressors such as diseases (e.g., due to the presence of one or more alleles providing resistance against the disease). In turn, the lack of genetic diversity in a population provides individuals with a poorer predisposition for resilience – e.g., if the population is infected by a disease, all the individuals within the population may get infected and die because of poor proliferation of resistant genes. Subsequently, low genetic diversity in a population can lead to extinction. Maintaining a high genetic diversity is also important to avoid problems due to inbreeding.  

It is well known that inbreeding has deleterious effects, because it allows recessive genes or alleles to become homozygous (i.e., carry two identical alleles because of common descent from an ancestor). It has been demonstrated that the genome of typical inbred mammals contains four or more loci that are homozygous for deleterious alleles. High rates of inbreeding can cause problems relating to fertility, immune response, birth defects, proliferation of unwanted gene mutations and unwanted heritable diseases. 

Maintaining the genetic diversity of a species is not only important between breeds, but also within breeds. The focus in commercial breeding is mainly on performance traits such as speed, endurance, and conformation, which may have negative effects on fertility traits such as reproductive endocrinology and subsequently establishment of pregnancy. Furthermore, commercial breeding, focusing on only a few breeds, contributes to the neglect of older native breeds, leading to the risk of loss of diversity and subsequently risk of extinction.  

Older native breeds carry various important features that could become vital in the face of climate change. These include traits such as disease tolerance, adaptability, rate of metabolism, calm temperament, and hardiness. For instance, the Fjord horse has adapted slow metabolism suitable for areas with poor vegetation. Traits relating to commercial/leisure use are also present in the native breeds. For instance, the Icelandic horse is known for its ability to tölt and pace, which is a result mainly from a mutation of the DMRT3 known to be involved in locomotion and gait. This subject is still being investigated, and recent findings suggest that there are other variants that may modify or perhaps even compensate for the «wrong» DMRT3-genotype. Subsequently, neglecting these breeds in favour of modern commercial breeds could contribute to loss of important genetic information.  

The Nordic native breeds descend from a few ancestors, and some only have one recognized ancestor (e.g., the Danish Knabstrupper and the Jutland horse). Several of the native horse breeds, including the Icelandic horse, Faroese horse, Gotland pony, Fjord horse, and Nordland/ Lyngen have suffered bottleneck events which have affected the rates of inbreeding in their populations. For instance, the Faroese horse suffered a severe bottleneck event in the 1960s, when only five individuals were alive. This led to a substantial increase of inbreeding in the 1970s that was still high in 1990 and 2004 when 48.2% of the population had an inbreeding coefficient corresponding to half-sib to full-sib mating and 11.3% had inbreeding coefficient above 30%. The average inbreeding rate in the Faroese horse population is substantially higher than what is reported in other breeds where the average inbreeding is usually lower than 10%. Monitoring for inbreeding provides important information regarding the breeding strategies that are used, and aids in gaining a better perspective of whether the population is stable or not. In Norwegian horse breeds, efforts to reduce increasing inbreeding coefficient have resulted in stabilisation in Nordland/ Lyngen, the Dole horse, and the Fjord horse. The trend is unfortunately still increasing for the Norwegian Coldblooded trotter, which could reflect the necessity to implement new breeding strategies. 

Further, modernization of agriculture and the second World War led to decline in the population of the different native horse breeds. Consequently, the current populations of the breeds are small and most of them are categorized as endangered. It is therefore vital to monitor and control the rate of inbreeding to avoid the risks and maintain as much genetic diversity as possible to conserve the breeds.   

Horses have been subjected to artificial selection for centuries for various purposes including transportation, agriculture, and warfare. At present breeding has mainly focused on breeding horses suitable for leisure and sport activities. Domestication and artificial selection have led to various alterations of in the equine genome. 125 genomic regions that are potentially affected by domestication have been identified. These regions can be classified into two groups: genes involved in physiological adaptations (i.e., genes affecting muscular and limb development, articular junctions, and the cardiac system), and tameness (i.e., genes affecting cognitive functions).  

Various of the genomic changes that have accompanied domestication are related to forelimb robustness, gaits, performance, behaviour, and cognitive skills. Coat colour has also been subjected to alterations due to domestication. Several of these traits are linked to neural crest cells, supporting the “neural crest hypothesis for domestication”. Mutations in genes affecting the tissues that originate from the neural crest cells have been found to cause several diseases, including lethal white syndrome and stationary night blindness. Genes causing the aforementioned diseases also affect coat colour. In general, modern breeding practices has increased the genetic load in horses and decreased diversity.  

Proliferation of detrimental genes linked to coat colour or other desired traits are not only present in commercial horses, but also occurs in the native breeds. For instance, breeding for the white colour in the Danish Frederiksborg horse allowed proliferation of the autosome recessive lethal white syndrome. Evidence also suggests that the leopard spotting allele in the Knabstrupper leads to stronger predisposition of developing insidious uveitis – consistent low grade inflammation causing damage to the eye. In the Swedish Ardennes horse type 1 Polysaccharide Storage Myopathy (PSSM) is the most common genetic disease. The disease is caused by a mutation of the glycogen synthase 1 gene (GYS1), and manifests as muscle pain, cell damage and muscle weakness, which leads to poorer well-being and performance. This mutation has been identified in up to 87% of draft horse breeds (not present in Fjord horse). Attributes such as slow metabolism allowing the Fjord horse to survive in sparse vegetation can elevate the risk of metabolic syndrome in this breed. Further, they are also susceptible to congenital disorders such as equine degenerative myeloencephalopathy (EDM) which affects the neurological system.  

Ossification of ungular cartilages is common in various breeds including Swedish Ardennes, North Swedish horse, Coldblooded trotters and Finnhorses, but the Icelandic horse is thought to have a genetic predisposition for this condition as well. They are also thought to be predisposed to osteoarthritis in the tarsal joints (bone spavin). Both conditions can be associated with injury, pain, and lameness (reduced welfare). Furthermore, studies have concluded that multiple congenital ocular anomalies (MCOA) syndrome is present in the Icelandic horse population, and that MCOA is segregating with the PMEL17 mutation. The PMEL missense mutation is also associated with the silver coat colour, which is a trait that is sought after in breeding. Identifying carriers of this mutation and breeding them with non-carriers would substantially reduce the risk of producing horses with vision threatening abnormalities caused by MCOA.  

Equine summer eczema (or insect hypersensitivity) affects various native Nordic horse breeds and has become an important issue in populations of both Icelandic horse and Finnhorse. Summer eczema impairs the welfare of horses and causes substantial financial loss to the owners. It appears to be a multifactorial disease, and occurrence and severity depends on both environment and individual genetic predisposition. Evidence suggests that susceptibility to summer eczema is hereditary and that improved breeding strategies can decrease the risk of developing summer eczema. Nevertheless, since the disease is multifactorial, the influence of genetic predisposition combined with different environmental factors need to be further studied to gain a more comprehensive information. This will prompt improved strategies for prevention and treatment of summer eczema.  

In the population of the commercial Norwegian-Swedish Coldblooded Trotter (NSCT), dynamic laryngeal collapse is the most common disorder of the upper respiratory tract. The condition also occurs in other trotter breeds and appears to correlate with anatomic phenotypes, and only occurs when the horse is exercised. A recent study detected a candidate genomic region as potentially important for the expression of dynamic laryngeal collapse, and further investigation within this region would improve our understanding of the underlying biological mechanisms of this disorder in horses.