With the sequencing of the equine genome in the last decade there is now an expanding and readily available spectrum of genetic technologies for a variety of applications in horses. Equine nutrition has always been an area of much research and interest in the past due to the effect diet can have on performance and health. The two terms nutrigenetics and nutrigenomics refer to the interactions between the genome and nutrition. Nutrigenetics particularly refers to how an individual’s unique genetic make-up affects their response to dietary nutrients. Nutrigenomics refers to how different types of food affect how the genes in DNA are “read” and which genes are “turned-on” or “turned-off”. This “turning-on” or “off” of genes is known as gene expression.
A good example of this in humans is celiac disease: when certain individuals eat gluten this affects gene expression and initiates an inflammatory reaction within the gut. Clinical signs of celiac disease can be vague but genetic testing can highlight gluten intolerance and can allow the individual to take steps to alter their diet before the symptoms become more severe.[vc_single_image image=”7533″ img_size=”410×340″ alignment=”right”]
In human nutrition the hope is to use genetic testing to plan “personalised nutrition” and several companies now exist which provide such genetic testing both alone and also in combination with other types of tests. The results of such testing are then used to design a personalised diet for the person undergoing the testing. The science however is still in its infancy and a greater understanding of all the factors, including genetic factors, which contribute to dietary effect on the body and physiological response to diet must be obtained.
Similarly to humans, each horse has a unique genetic composition or “genotype” which means that each horse may respond differently to nutrients in the diet. Therefore, what is observed in real life or the “phenotype” of the horse will be affected directly by both diet and the individual horse’s unique genotype.
Two examples in horses of genotype interaction with nutrition resulting in a real life clinically observable disease include:
Polysaccharide Storage Myopathy type 1 (PSSM1) is a form of a chronic tying-up disease in horses. There is a genetic defect present in the mechanism of storage of glucose obtained from the diet as muscular glycogen. It is observed frequently in American Quarter horses and related breeds, Draft horse breeds (especially Belgian Drafts) and Warmblood breeds but has also been diagnosed in many other breeds. Clinical signs can include stiffness, awkward gait, pain on palpation, reluctance to move, sweating and brown coloured urine. Episodes are increased by high grain diets. The genetic cause of PSSM1 is known and a genetic test can identify a horse with the disease. This allows the diet to be modified by reducing grain or using one of several commercially available feed formulations specifically designed for these horses.
Hyperkalemic Periodic Paralysis (HYPP) is a muscular disease caused by an inherited genetic mutation which affects sodium channels in skeletal muscle cells. The disease affects American Quarter Horses and related breeds. Clinical signs observed can include muscle twitching, weakness and even collapse after exercise or stress. A genetic test is available which can identify horses with this disease. Once a positive test is returned a change of diet is a large aspect of the advised treatment/management strategy. The feeding regime usually includes avoiding high potassium feeds, such as alfalfa, and providing many small feeds during the day and also preventing dehydration.
These are two examples of situations in horses where a genetic test can be carried out to identify horses with certain genotypes that are at high risk to develop the disease. Once identified, a change to the diet can be initiated which results in reduction or prevention of the manifestation of the disease. There are several other diseases in horses in which diet is a large contributing risk factor that are the subject of genetics research, such as for example laminitis. The aim of the research is to identify horses at high risk of developing the disease, increase understanding of the interaction of specific parts of the genome in these horses with the different nutrition components of the horse’s diet and to formulate specific diets as part of a treatment/management plan.
The next logical step from this work is to look at healthy individuals and to harvest the information contained within their genotypes to tailor a specific diet to the individual based on this data. The aim of this approach is to fine tune performance for competition and to promote optimal health and immunity in the healthy individual.
The requirements and reactions to specific foods of one horse may be completely different to those of the horse in the next stable regardless of similarities between breed, sex, age etc. One contribution to these differences is the naturally occurring genetic variation among individuals. Individually tailored diets may be composed, in theory, of either large changes such as increasing or decreasing relative proportions of certain key nutrients (e.g. fats, carbohydrates etc.) or may include the identification of specific single molecules which are required at higher concentrations in the diets of certain individuals only (e.g. amino acids, metabolic molecules, molecules involved in energy metabolism, etc). Such genetic tests could also potentially be used to identify “deficiencies” of certain molecules in specific individual horses or the genetic requirement for higher dietary concentrations of these molecules within these horses.
While the field of study of nutrigenetics/genomics is in the early stages there are already well documented examples of disease situations where using the data gained from genomic evaluation to amend or alter individual diets has had a hugely positive impact on well-being. There is still much understanding to be gained about the interactions between the genome and diet but it is only a matter of time before the next example of a real life application within the field is discovered. Specifically within the equine industry in which horses compete so regularly and at such high intensity there is an appetite to improve the performance efficiency within competition as well as overall health. Individualised diets may be one realistic option to achieve this.