Did you know that what your horse eats effects his genes? With a better understanding of nutrigenomics, we can be better equipped to meet the nutritional needs of our equine companions.
We have come a long way with how we feed horses. It started by providing horses some land to graze and supplementing their diets with grains or concentrates and other feedstuffs. Equine nutrition has become much more sophisticated since then. Now we can select specific forages for pasture and hay production and follow soil nutrient and harvesting recommendations to provide optimal hay and pasture. We also have a large variety of feeds and supplements to select from to meet our horses’ nutrient requirements. Following is a discussion on nutrigenomics – what it is, how it’s possible, examples of how nutrients can interact with the horse’s health, and how nutrigenomics can affect the future of feeding horses.
Nutrigenomics is the scientific study of how nutrients can interact, directly or indirectly, with an animal’s genome. This interaction influences how genes are expressed, which can affect health, disease and performance.
Genes are chains of DNA found in the nucleus of each cell of the horse’s body. These genes serve as blueprints and their DNA is copied to make specific mRNA which are used as templates to make specific proteins. These specific proteins are chains of amino acids that are used by the cell to make structural components (i.e. tendons, ligaments, muscles) and functional components (e.g. enzymes that digest nutrients and regulate metabolism of nutrients to produce energy).
The term “gene expression” refers to how genes produce proteins. Specific genes can be turned on (upregulation) or turned off (downregulation). Genes that are upregulated produce more of a specific mRNA and downregulated genes produce less of a specific mRNA. In other words, one or more genes can make a key to “turn on” or “turn off” a metabolic sequence. This key starts at the cell’s genetic material or DNA and goes to the assembly plant in the cell, which is the ribosome. The ribosome then makes more or less of what that key tells it to, and that results in the metabolic sequence that causes the “expression” of that gene.
Technological advances make nutrigenomics possible
Nutrigenomics is now possible due to advances in genetic technology. One new discovery is polymerase chain reaction (PCR). PCR allows a small sample of DNA to be taken and quickly reproduced into millions of copies that can be studied. The entire equine genome has been identified using PCR and was made public knowledge in 2007.
Another genetic advance is a DNA or gene “chip”. A gene chip is specific genetic material that has been taken from a DNA string and then replicated many times by PCR and placed in a microarray structure. The chip is a small plate of glass in a plastic case about the size of a postage stamp. On the surface of the gene chip are thousands of DNA sequences make of specific genes. A researcher obtains a DNA sample, chops it into small pieces, dyes it and places it in with the original DNA material in the chip. Replication of DNA material continues for a specific amount of time and then a scan of the chip is used to measure the amount of sample DNA that binds to the original DNA. The bound or complementary DNA in the gene chip can then be measured and show what genes have been upregulated or downregulated.
Using nutrigenomics to improve horse health
Following is an example of how a nutrigenomics experiment could be performed. Two groups of horses are selected and fed diets that vary in a certain nutrient amount or dietary condition. Gene chips are made with genes from tissue thought to be influenced by this dietary nutrient or condition. DNA samples from each horse’s tissue are added to gene chips from both groups. The chips are scanned and the results are used to determine if genes from the sampled tissue from either group of horses are expressed differently due to the nutrient amount or dietary condition.
We know that nutrients can interact with genetic expression to impact a horse’s health. For example, Hyperkalemic Periodic Paralysis (HYPP) is a genetic disease that causes symptoms including muscle spasms, trembling and weakness in affected horses. HYPP is the result of a mutation that causes changes in the expression of a gene that transports sodium in and out of skeletal muscle. This sodium transport mechanism uses sodium to regulate potassium, which is known as the sodium-potassium pump. In the presence of high dietary potassium in horses with the defective gene, the sodium transport fails to activate, and potassium levels increase greatly above normal and symptoms of potassium toxicity occur.
Another example of a genetic expression impacting the horse’s normal health is Polysaccharide Storage Myopathy Type 1 or PSSM1. PSSM1 can cause episodes of muscle weakness, stiffness, pain and muscle damage after exercise, and is also known as “tying up” or exertional rhabdomyolysis. PSSM1 is caused by a mutation in the glycogen synthase gene. This mutation causes muscle cells in the horse to continually produce glycogen from blood glucose. When blood glucose is readily available, it results in an excessive amount of muscle glycogen stored in an abnormal form that can’t be readily mobilized during exercise. This lack of available glucose to fuel the muscle cells causes symptoms of PSSM1. High levels of dietary nonstructural carbohydrate (NSC) or starch and sugars can induce or increase the incidence of PSSM1. The treatment for PSSM1 is a low NSC, high-fat diet, with selection of a low NSC concentrate and a low NSC hay may be required as well.
More studies are needed
Nutrigenomics is still in the early stages with only a few studies done in the horse and not many performed with other animals and humans. Some recent areas of investigation have been 1) a low-calorie diet with obese humans and the effect on oxidative stress and inflammation-related genes, 2) osteochondrosis-related gene expression of equine leukocytes in the joints of foals, and 3) the effect of high dietary selenium supplementation on gene expression in sheep.
The goal of equine nutrigenomics is to tailor a horse’s diet based on their genetic information, so they grow in a healthy state and avoid developmental and metabolic issues. Unfortunately, this goal hasn’t been realized yet, and there are several areas that need further research for success to be achieved.
- First and foremost, a better understanding of genes is needed. While we know the entire genome of the horse, or all the genes and their sequences that make up the entire horse, there is not much information on what each gene is or does.
- A second limitation is the difficulty in obtaining enough sample sizes from many target tissues because of the necessity of euthanizing horses to do so. So currently, mainly skeletal muscle and white blood cells are used for nutrigenomic research.
- Other limitations include a lack of horses with data on specific dietary needs for research, and lack of funding for research on equine nutrigenomics.
In the future we may be able to determine a horse’s genetic information and evaluate which genes dietary conditions and nutrients influence. This will allow nutritionists to develop feeds and supplements with different amounts and forms of nutrients (i.e. organic versus inorganic), feed additives (i.e. prebiotics, probiotics, antioxidants) and dietary recommendations (e.g. reduced calorie, low NSC, low potassium) that veterinarians and caretakers can utilize to provide better feeding results for horses.