About natural supplements · Dec 21, 2012
Horses are herbivores, their supplements should be vegetarian
From fish-oil capsules to shellfish-derived glucosamine, the equine supplement industry routinely feeds animal products to an animal whose entire digestive system evolved to process plants.
Horses are strict herbivores whose digestive anatomy and genomics are built entirely around plant material, they even carry herbivore-specific gene losses in fat-digestion enzymes absent in omnivores and carnivores. Their hindgut relies on microbial fermentation of fibre, not the digestion of animal tissue. Every ingredient commonly sourced from animals, fish oil, shellfish-derived glucosamine, gelatine, has a viable plant-based alternative, yet the long-term effects of routine animal-product ingestion in horses remain unstudied.
Common misconception: Fish oil is the only meaningful omega-3 source for horses
I understand why this idea took hold. Marine-derived EPA and DHA do achieve higher plasma and tissue concentrations than plant-based sources, and that finding is real [13]. But the conclusion that fish oil is therefore the only serious option is a leap the evidence doesn’t support, and it ignores some significant problems with fish oil itself.
Fish oil production is bound up with overfishing and habitat destruction, and despite extensive processing, detectable concentrations of contaminants including polychlorinated biphenyls (PCBs) remain in some products [4]. That is not a trivial concern when you are supplementing an animal daily over months or years.
The plant-based alternatives are more robust than the industry gives them credit for. Flaxseed oil improved lipid profile, haematological parameters, and antioxidant defence mechanisms in horses in direct comparison with soybean oil [5]. Camelina oil, tested over a 16-week trial, performed equivalently to flaxseed oil across coat quality, skin health, and inflammatory markers, and costs less [12]. Horses can convert plant-derived alpha-linolenic acid (ALA) from these oils to EPA and DHA endogenously, and both flaxseed and camelina are recognised as viable ALA sources in equine nutrition [11]. Yes, conversion efficiency is limited compared to direct marine supplementation [11][13], but for the majority of horses not competing at elite level, plant-based oils deliver meaningful omega-3 benefit without the sustainability and contamination baggage.
Algae, which is where fish get their DHA in the first place, is also emerging as a clean, controllable alternative, cultivated in contained environments that eliminate the contaminant risk entirely [1][4].
The honest position is this: fish oil works, but it is not irreplaceable, and for a strict herbivore whose digestive system evolved entirely around plant material [2][3][7][9], defaulting to a marine animal product when effective plant-based alternatives exist is a choice worth questioning.
Why a horse’s biology is built for plants, not animal products
Horses are hindgut fermenters whose digestive system has evolved specifically around plant fibre. They lack the enzymatic diversity to break down plant tissue independently, instead, resident microbial communities in the large intestine perform fibrolysis, yielding short-chain fatty acids (acetate, propionate, and butyrate) as the horse’s primary energy substrates.
This herbivore specialisation goes deeper than diet habit. At the genomic level, horses have lost functional expression of pancreatic lipase-related protein 1 (PNLIPRP1), a fat-digestion enzyme present in meat-eating and omnivorous species, representing a hard-wired, herbivore-specific adaptation.
When it comes to omega-3 fatty acids, plant-based sources such as flaxseed oil and camelina oil supply alpha-linolenic acid (ALA), which horses can convert endogenously to the longer-chain EPA and DHA, albeit at limited efficiency. Algal oil delivers EPA and DHA directly without relying on fish, and studies in cats confirm it raises serum concentrations of both fatty acids comparably to fish oil. Flaxseed oil supplementation in horses has been shown to improve lipid profile and enhance antioxidant defence mechanisms. A 16-week trial comparing camelina, flaxseed, and canola oils found all three improved coat quality equally, with no significant differences between them.
Fish oil, by contrast, requires extensive processing to remove contaminants including polychlorinated biphenyls (PCBs), and detectable concentrations of various contaminants have been reported even after processing.
Choosing plant-based supplements for your horse: what the evidence actually supports
Omega-3 fatty acids: plant oils are a legitimate choice
If you’re supplementing omega-3s, the evidence supports several plant-based options. Flaxseed oil and camelina oil are both viable sources of alpha-linolenic acid (ALA), and a 16-week trial found no significant difference between camelina, flaxseed, and canola oil in coat quality or measured inflammatory markers in horses [12]. Horses can convert ALA to the longer-chain EPA and DHA endogenously, though the conversion is limited [11]. If you specifically need to raise plasma EPA and DHA levels, for example, in a joint or inflammatory protocol, marine-derived sources do achieve higher tissue concentrations [13]. Algal oil is worth noting here: it delivers DHA directly, is produced in controlled environments free from the contamination concerns associated with fish oil, and carries none of the overfishing burden [1, 4].
On glucosamine and chondroitin
If you are using these for joint support, understand that most conventional products are derived from shellfish, shrimp, crab, or beef, animal-derived ingredients fed to an animal whose digestive system evolved entirely around plant material [9, 10]. Plant-sourced glucosamine is available; it is worth asking your supplier specifically. (The Herbal Horse uses a plant based glucosamine.)
Supporting the hindgut first
Before reaching for any supplement, remember that horses are hindgut fermenters whose entire energy and health economy is built on fibre fermentation. The microbes that do this work produce short-chain fatty acids, acetate, propionate, butyrate, that underpin everything else [2, 7]. Forage-based feeding, not grain concentrates, is where the research consistently points for health, welfare, and performance [3]. No supplement compensates for inadequate fibre intake [8].
Long-term use of animal-derived ingredients
Carry-over effects and long-term safety of novel feed additives remain insufficiently studied [6]. We do not have a clear picture of what chronic ingestion of animal-derived ingredients does in a species whose genome has shed the fat-digestion enzymes that carnivores and omnivores retain [9]. That absence of data is not proof of harm, but it is a reason to apply the precautionary principle, particularly when plant-based alternatives exist and perform comparably.
What we’d recommend
Plant-based glucosamine supports equine joint health without the contaminants and sustainability concerns of fish oil.
See the product
Frequently asked questions
Are horses naturally vegetarian, or can they digest animal-derived ingredients?
Horses are strict herbivores whose entire digestive system is built around plant fibre. Their hindgut relies on microbial fermentation to break down plant material into short-chain fatty acids for energy. Genomic research has confirmed herbivore-specific gene losses in fat-digestion enzymes, the horse pancreas does not even express PNLIPRP1, a lipase present in meat-eating and omnivorous species. There is no evolutionary precedent for processing animal-derived ingredients.
Why are so many horse joint supplements made with shellfish or beef, and does it matter?
Glucosamine and chondroitin are commonly sourced from shellfish, shrimp, crab exoskeletons, and beef, animal tissues a horse would never encounter in nature.
Is fish oil a good omega-3 source for horses?
Fish oil delivers EPA and DHA efficiently, but it comes with real problems: dwindling fish stocks, overfishing, habitat destruction, and contamination with PCBs that require extensive processing to remove, and are sometimes still detectable afterwards. Plant-based oils such as flaxseed and camelina provide ALA, which horses can convert to EPA and DHA, making them a workable and far more sustainable alternative.
Can algal oil replace fish oil for omega-3 supplementation?
Yes, and it is the more defensible choice. Algae are the original source of marine omega-3s, fish accumulate EPA and DHA by eating them. Algal oil can be cultivated in controlled environments, which eliminates contaminant risk and removes pressure on marine ecosystems. Research in companion animals confirms it raises serum EPA and DHA comparably to fish oil.
What plant-based oils actually work for horses that need omega-3 support?
Flaxseed oil and camelina oil are both well-supported. Flaxseed oil has been shown to improve lipid profile and antioxidant defence in horses compared with soybean oil. A 16-week trial found camelina oil equivalent to flaxseed for coat quality, skin health, and inflammation markers. Both provide ALA, which horses convert, albeit at limited efficiency, to the longer-chain EPA and DHA.
Sources
- Effects of algal oil as an alternative to fish oil in feline foods on serum concentrations of eicosapentaenoic acid and docosahexaenoic acid
- Understanding the microbial fibre degrading communities & processes in the equine gut
- Review: Feeding conserved forage to horses: recent advances and recommendations
- The effects of a plant-based and a plant- and marine-based n-3 oil supplement on behavioral reactivity, heart rate variability, and plasma fatty acid profile in young healthy horses
- Effect of Dietary Flaxseed Oil Supplementation on the Redox Status, Haematological and Biochemical Parameters of Horses' Blood
- Bioactive feed additives in animal nutrition: bridging innovation, health, and sustainability
- Understanding the microbial fibre degrading communities & processes in the equine gut
- The Fibre Requirements of Horses and the Consequences and Causes of Failure to Meet Them
- Convergent gene losses illuminate metabolic and physiological changes in herbivores and carnivores
- Low quality of evidence for glucosamine-based nutraceuticals in equine joint disease: review of in vivo studies
- The balance of n-6 and n-3 fatty acids in canine, feline, and equine nutrition: exploring sources and the significance of alpha-linolenic acid
- Effects of dietary camelina, flaxseed, and canola oil supplementation on transepidermal water loss, skin and coat health parameters, and plasma prostaglandin E2, glycosaminoglycan, and nitric oxide concentrations in healthy adult horses
- Effects of two different dietary sources of long chain omega-3, highly unsaturated fatty acids on incorporation into the plasma, red blood cell, and skeletal muscle in horses