The conversion step horses depend on — and why it often falls short

When omega-3 is fed as ALA, the body has a job to do before it can use it. That job is harder than it sounds.

---

In our last post, we established that ALA is a short-chain omega-3 — a building block that the body needs to convert into EPA and DHA before it can put those molecules to work. This post looks at how that conversion actually happens, and why it so often falls short.

What conversion actually means

When the horse eats ALA — from linseed, fresh grass, or any plant-based source — that molecule enters the body as an 18-carbon chain. EPA has 20 carbons. DHA has 22. To get from ALA to EPA and DHA, the body has to physically extend and modify that chain, adding carbons and adjusting its structure step by step.

This is not a single process. It is a sequence of steps, each one carried out by a specific enzyme. Think of it like a production line. ALA arrives at the start. Each station on the line does one job — extending the chain, adding a double bond, modifying the structure slightly. By the end of the line, if everything has gone to plan, the body has produced EPA and then DHA.

The key enzyme that starts this production line performs the first and most important step in the conversion. Without it, the process cannot begin.

Why the production line is unreliable

Here is where the problem starts.

This enzyme is not exclusively dedicated to converting ALA. It is a shared resource. The same enzyme is also needed to process omega-6 fatty acids — the other major family of polyunsaturated fats, which are abundant in most modern equine diets, particularly in grains and compound feeds.

When the diet is high in omega-6, those fatty acids compete directly with ALA for access to the same enzyme. And omega-6 tends to win that competition. The enzyme preferentially processes omega-6 over omega-3, which means that when both are present in significant quantities, ALA conversion is pushed to the back of the queue.

The result is that even when ALA intake is generous, the production line may be running slowly — or in some cases barely running at all — because the key enzyme is occupied elsewhere.

What the research shows

This is not a theoretical concern. Studies in horses have examined what actually happens to EPA and DHA levels when ALA is supplemented — and the findings are consistent.

When horses are given ALA-based supplements, EPA levels in the blood can sometimes increase modestly. DHA levels typically do not change at all, even when ALA intake is substantially increased.

That last point is particularly significant. DHA is the long-chain omega-3 that accumulates most in the body's tissues — in joints, airways, muscle, and skin. If DHA does not rise in response to ALA supplementation, those tissues are not receiving more of the molecule that is most relevant to the effects omega-3 is expected to produce.

Feeding more linseed does not reliably solve this. The constraint is not in the amount of ALA available. It is in the capacity of the production line to process it.

Why this varies between horses

One of the more frustrating aspects of ALA-based supplementation is that outcomes are inconsistent. The same product, fed at the same dose, produces a clear response in one horse and nothing obvious in another.

This variability now makes more sense. Conversion efficiency is not fixed. It depends on the balance of omega-3 to omega-6 in the overall diet — a diet higher in omega-6 creates more competition for that enzyme, reducing conversion further. It also depends on the metabolic state of the horse — factors like age, workload, and underlying health can all influence enzyme activity. And there are individual differences in enzyme levels — some horses simply have more of this enzyme available than others, meaning their production line runs more efficiently under the same conditions.

The practical consequence is that two horses receiving identical supplementation may be producing very different amounts of EPA and DHA internally. What looks like a consistent input is producing an inconsistent output.

The implication

If the constraint sits in the conversion step itself, increasing the amount of ALA being fed is unlikely to solve it. The production line has a capacity limit, and pushing more raw material in does not expand that capacity.

The only way to reliably get EPA and DHA into the tissues is to provide them directly — bypassing the production line entirely and delivering the finished product rather than the raw material.

That is what algae-derived omega-3 does. And once EPA and DHA are being provided directly, the question shifts: not whether the conversion is working, but whether the dose is sufficient and consistent enough to make a difference.

---

References

Hansen et al. (2002); Vineyard, Warren & Kivipelto (2010) — studies in horses showing that ALA supplementation can raise circulating EPA modestly but does not raise DHA, even when ALA intake is substantially increased.

Linus Pauling Institute — Essential Fatty Acids (lpi.oregonstate.edu/mic/other-nutrients/essential-fatty-acids) — establishes that LA and ALA compete for the same enzymes, and that human studies estimate conversion of ALA to DHA at 0–4%.

Note: conversion efficiency data is drawn from human and cross-species research. The enzymatic pathway is shared across mammals, but specific conversion rates in horses have not been fully established. The equine studies cited above address the output — what actually appears in blood and tissue — rather than the conversion rate directly.