Elizabeth Gormley
Equine genetics is not only useful for horse breeders
Equine genetic discoveries can help the entire equine industry reduce the causes of many historically unsolvable problems.
One area of science that is relevant to all aspects of the equine industry is genetics. Reduction in risk of investment is a vital concern for the horse breeder, trainer, seller and consumer. The growth and function of the entire horse industry is influenced by public perception leading to public policy. Animal welfare issues have become a high priority in modern society. Known modes of inheritance give all sectors of the equine industry the possibility to make the choice of risk reduction concerning equine resources. Reduction in the availability of deleterious heritable genetic traits in breeding horses has a direct effect on the welfare of all equines. Identification of genetically influenced disease etiologies and mechanisms enabled by genetic science increases horse welfare through proper treatment of equine health problems, and additionally assists in the understanding of corresponding human illnesses.
The reduction of investment risk is vital to the success of any horse breeding or sales endeavor. Potential buyers have a common interest together with the producers concerning the value of available horses. Veterinary genetic science is linked to market value of horses by giving a prognosis of the relative risk involved for the occurrence of a bad gene trait with associated certain physical characteristics called phenotype. Ability to predict horse health problems that both lower the value of horses on the market, and those that cause decreased welfare of horses being trained or asked to perform increases consumer confidence and public perception of the equine industry.
Knowledge of modes of inheritance can reduce wastage of horses in several ways. Elimination of animals with deleterious heritable traits can cause a breeder to avoid wasting financial resources on horses with poor prognosis of performance longevity and value. This will avoid the situation where a horse is trained while concurrently suffering from disease. Wastage is also prevented when valued genetic traits are preserved. Knowing where and how the deleterious gene(s) reside and behave avoids the elimination of breeding animals with rare traits of value from being culled from the gene pool. Improvements in the understanding of disease mechanisms on the molecular level will enable breeding to be more efficient, and training can yield lasting drug free progress. Sustainability increases as a result of these improved efficiencies allows all aspects of the horse industry to grow.
Communication between breeders, scientists, veterinarians, trainers, and other horse industry components produces far reaching positive effects. Collaborations between breeders and researchers allow especially rapid progress in reduction of heritable diseases in the horse industry. Examples include several breed registries that have genetic counseling information available for the prevention of production of horses with SCID, Overo lethal white syndrome, and HYPP. Other deleterious heritable traits that impact quality of performance are often a cause for insidious health and equine welfare problems, such as malignant hyperthermia and PSSM. Environment x gene interactions are linked with the efficient use of equine resources.
According to researcher Susan L. Ewart College of Veterinary Medicine, Michigan State University, USA there are many ways in which genes and the environment interact. "The environment can have a direct impact on DNA, for example, ionizing radiation and reactive oxygen species directly damage exposed DNA, resulting in the initiation of DNA repair mechanisms, which may or may not be fully successful. More recently, it has become clear that the environment can also alter DNA in ways that do not interrupt the DNA strand or change nucleotide sequence. Termed "epigenetics," these mitotically or meiotically heritable DNA modifications result in changes in gene expression, as epigenetic changes typically make DNA sequence unavailable for transcription and thus modified genes are effectively "silenced." Epigenetic changes include DNA methylation, histone modifications (methylation, acetylation, phosphorylation, and ubiquitination), genomic imprinting, and X-chromosome inactivation" states Ewart.
Many of these examples occur at differing specific times during growth and development and will be covered in future Science of Motion articles on this page. A notable example of the complexity of gene x environmental interactions affecting risk of investment in equine resources would be the disease of equine recurrent airway obstruction, RAO. Interesting are the findings that not only is the disease inherited through various genes working in different ways, but horses with the disease are also genetically programmed for increased parasite resistance.
According to investigators at Equine Clinic, Department of Veterinary Clinical Studies, Vetsuisse-Faculty, University of Berne, and Institute of Genetics, Vetsuisse-Faculty, University of Berne, Haras National, Avenches Switzerland, and Animal Health Trust, Newmarket, Suffolk "Segregation analyses of this family material indicate that the mode of inheritance of HOARSI (horse owner assessed respiratory signs index) is characterized by major gene effects; interestingly, in one family mode of inheritance is autosomal dominant, whereas in the other family it is autosomal recessive (Gerber et al. 2009; in press JVIM). Based on these segregation analysis results, and the locus heterogeneity suggested by the findings of Jost et al. (2007; see abstract by J. Swinburne), we hypothesize that several major genes are responsible for RAO and that they may differ between families."
Additionally the researchers stated "In the course of these studies, we also explored another novel aspect of RAO. We had observed that the RAO-affected horses appeared to be less parasitized than healthy pasture mates and had identified IL4R as a candidate gene for RAO based on an association with microsatellite markers near the gene (Jost et al. 2007; see also abstract by J. Swinburne) and on an increased gene expression (Gerber, unpublished results), both observed in sire 1, but not in sire 2 offspring. IL4R??is associated with asthma and atopy as well as with parasitic defense in humans and animals. Based on these observations and evidence for an inverse relationship between asthma and resistance to parasites, we postulated that RAO-affected horses have a decreased chance for shedding helminth eggs compared to their healthy pasture mates living under the same environmental conditions. We found that members of the family showing the association of RAO with IL4R??(sire 1 family) had a 7.3-fold decreased chance for a severe infection with strongylid nematodes (>100 eggs per gram feces) compared to unrelated pasture mates (no such effect was observed in the sire 2 family). Furthermore, unrelated RAO-affected animals were more resistant against strongylid nematodes when compared to their healthy pasture mates."
A horse living in regions of high parasitism but low in environmental RAO disease initiation triggers may allow a horse to be adapted to suitable environments, reducing disease associated preventable problems. Future articles relating to genetic influences on equine sports performance, health, longevity and welfare will include topics such as paternal, maternal or reproductive technological influences on heritable traits progeny are born with. The genetic influences linked with behavior and their effects on training will also be explored in upcoming material.
Eliabeth Gormley
Elizabeth has a background in veterinary medicine and animal sciences (veterinary ophthalmology, and animal biology). She has worked in academic veterinary research at University of Florida (managed veterinary ophthalmology research and academic labs), and at the UF human orthopedic tissue bank during my time in college. Elizabeth owns and manages E and E Farm in Ocala, FL together with Eduardo Arellano DVM.
Elizabeth has a current specific interest in equine sports medicine, equine pharmacogenetics -the study of inherited differences (variation) in drug metabolism and response, equine reproductive physiology, and equine growth and development interactions with exercise and conditioning programs.
In her spare time she likes show jumping, music, and gardening.
References
1. Genetics of equine RAO
Vincent Gerbera, Alessandra Ramseyerc,a, Eva Laumena, Päivi Nussbaumera, Jolanta Klukowska-Rötzlerb, June E Swinburned, Eliane Martib, Tosso Leebb, Gaudenz Dolfba Equine Clinic, Department of Veterinary Clinical Studies, Vetsuisse-Faculty, University of Berne, and bInstitute of Genetics, Vetsuisse-Faculty, University of Berne, Haras National, Avenches Switzerland, and dAnimal Health Trust, Newmarket, Suffolk CB8 7UU, U.K. World Equine Airways Symposium 2009 (WEAS 09)
2. Complexities of Gene × Environment Interactions
Susan L. Ewart College of Veterinary Medicine, Michigan State University, USA World Equine Airways Symposium 2009 (WEAS 09)
3. EQUINE MOLECULAR GENETICS - UPDATE AND PERSPECTIVES
Gérard Guérin
INRA, Centre de Recherches de Jouy, Laboratoire
de Génétique biochimique et de Cytogénétique,
78352, Jouy-en-Josas, Cedex, France
Proceedings of the 9th International Congress of World Equine Veterinary Association, 2006 - Marrakech, Morocco
4. WBFSH Seminar "Breeding for an improved health, longevity, and welfare in horses." Copenhagen, Denmark November 3rd-4th 2009.
