Fatty acids are organic macromolecules derived from hydrocarbons that are composed of chains of carbon and hydrogen atoms and are the structural basis of fats and lipids. They are very diverse molecules, which differ from each other by the length of their hydrocarbon chains and the presence, number, position and/or configuration of their double bonds. Fatty acid molecules perform important functions at the cellular level, which makes them essential components for health, and for this reason they must often be obtained through the diet.
Omega-3 fatty acids are a class of polyunsaturated fatty acids with recognized health benefits. They are found in a variety of food sources including oily fish, krill and squid. The main Omega-3 fatty acids that have shown evidence of health benefits are eicosapentaenoic acid or EPA and docosahexaenoic acid or DHA.
In recent years, there has been increasing interest in learning more about the effects of these fatty acids on animal health. In this review we will focus on the benefits they provide to equine health.
General information about Omega-3
Polyunsaturated Fatty Acids (PUFA) are Essential Fatty Acids for the normal growth and development of multicellular organisms. Within PUFA we find two main groups: Omega-3 (ω-3) and Omega-6 (ω-6) fatty acids, which are Essential Fatty Acids (EFA) for humans because we lack the enzymatic machinery necessary to biosynthesize them.
The "ω" nomenclature considers the carbon atom of the terminal methyl group of the fatty acid as the main carbon and identifies the first double bond closest to this chemical group. The first exponent of the omega-3 fatty acids is α-Linolenic acid (ALA; C18:3) which via desaturases and elongases can be transformed into Eicosapentaenoic acid (EPA; C20:5) and subsequently in to Docosahexaenoic acid (DHA; C22:6). The first exponent of the ω-6 fatty acids is Linoleic Acid (C18:2)
Polyunsaturated Fatty Acids: Metabolization of ω-6 and ω-3 polyunsaturated fatty acids.
Desaturation and elongation pathways of Linoleic and α-Linolenic acids (Valenzuela et al., 2011).
The main sources of ALA in the diet are through plant sources, while EPA and DHA are obtained mainly from fatty fish such as salmon, some algae and krill (Bus et al., 2019). For horses the most common sources of Omega-3 Fatty Acids used in the diet, are flaxseed oil, soybean oil and fish oil.
However, soybean and flaxseed oils are of vegetable origin, therefore, their main source of Omega-3 is α-Linolenic acid (ALA). While the main source of Omega-3 in fish oil is EPA and DHA.
The ability of horses to bioconvert ALA to EPA and DHA has not been determined, but should be less than that of humans. It is known that the rate of bioconversion of ALA to EPA in humans is less than 10% and that of ALA to DHA is less than 0.10%. In addition, it was observed that, feeding horses with fish oil significantly increased the concentration of circulating EPA and DHA in plasma (Piccione et al, 2014).
Daily supplementation with EPA and DHA has been shown to reduce the production of pro-inflammatory cytokines, such as interleukin-1, interleukin-6, interleukin-8 and tumor necrosis factor-α (TNF-α) that are released when macrophages and monocytes are activated (Camuesco et al, 2006). Although these cytokines act as potent activators of immune function, excess activity of these substances contributes to pathological inflammation, a situation observed in chronic intestinal inflammation, rheumatoid arthritis, among other inflammatory pathologies (Valenzuela et al., 2011).
The precedents show that, both in humans and animals, the consumption of ω-3 PUFA should be increased through foods rich in EPA and DHA, or develop functional foods that contain them in therapeutically useful concentrations, in addition to considering the complementary consumption of nutritional supplements (nutraceuticals) with ω-3 PUFA.
Benets of Omega-3 in joints
In horses that are exposed to high impact sports such as racing, enduro among others, as well as those that are used for loading, it is recurrent that lameness or chronic pathologies affecting the legs are presented, which can mean shortening the life of the horse. For this reason, the use of drugs is very recurrent to alleviate the pain caused by such lameness. But in recent times, different alternatives have been studied, such as supplements that help to reduce inflammation and therefore pain. Following this line, it has been studied that fish oil supplementation can improve the inflammatory response of horses in constant training and potentially improve their health status. Due to the effect that EPA and DHA have on the lipid membrane of the cell,this may improve signal transduction and gene expression. These events could favor the transport and binding of IL-1Ra (Proinflammatory)
to its receptors, thus reducing the response to the inflammatory process (Piccione et al, 2019).
In addition, in processes such as arthritis, supplementation with Omega-3 favors the treatment of this pathology and decreases the concentration of prostaglandins in the synovial fluid which in turn helps to decrease pain, thus improving the condition of the specimen. It is suggested to use it in laminitis and other equine foot pathologies.
Additionally, it has been observed that in pathological processes such as osteoarthritis (inflammatory and degenerative joint process), the use of Omega 3 decreases the expression of proinflammatory molecules in synovial fibroblasts, which suggests that it could favor joint health both in a state of full health and in a pathological situation (Caron et al., 2019).
Benets of Omega-3 on reproductive activity
Several studies report on the fertility of stallions and mares, as well as in other species such as cattle, pigs and humans. EPA and DHA supplementation in mares, regulates the synthesis of Prostaglandins, thus increasing progesterone levels, favoring embryo survival. On the other hand, multiple studies indicate the benefits of supplementing lactating mares, due to the transfer of these fatty acids to foals through milk, having a stronger immune system than foals fed from mares not fed omega-3 fatty acids (Hernandez, 2018).
Robert (2015), studied the effects of incorporating omega-3 fatty acids into the uterine environment in mares and on gene expression in their embryos. The study reports that the expression of genes responsible for the transport of nutrients to the embryo tended to increase in mares supplemented with omega 3 (DHA) (see Figure 2).
On the other hand, stallions supplemented with EPA and DHA sources have shown an increase in the number of spermatozoa with normal morphology, post-freezing motility, a decrease in the percentage of atypia, a decrease in sperm mortality and an increase in sperm concentration (Hernández, 2018).