Lucerne, Insulin, Protein and Weight: Untangling the Confusion for Metabolic Horses

Lucerne (alfalfa) is one of the most debated forages when it comes to metabolic horses. Some professionals actively recommend it, while others advise avoiding it altogether. Horse owners are often left confused by conflicting advice, particularly when managing insulin dysregulation, equine metabolic syndrome (EMS), PPID Cushing's disease) or laminitis recovery.

The reality is more nuanced.

Understanding why requires separating insulin response, energy intake and protein load – three factors where insulin response to sugars and starch is well recognised, but the indirect effects of energy and protein load on metabolic stress and insulin sensitivity are often overlooked.

Lucerne and Insulin: Clearing Up the Sugar Myth

Lucerne is a legume, not a grass. This matters because legumes store carbohydrates differently.

Lucerne is typically low in ethanol-soluble carbohydrates (ESC; simple sugars) and starch and therefore does not cause post-feeding insulin spikes when appropriately selected. Australian laboratory datasets consistently show lucerne hay testing in the low to moderate range for non-structural carbohydrates, with water-soluble carbohydrates (WSC) commonly around 4–12% DM (dry matter) and starch generally low, often below 5% DM, though individual samples can fall outside these ranges.

WSC represents the sum of  ESC and fructans; fructan content in lucerne is considered negligible. For metabolic horses, the commonly accepted target is a combined ESC + starch intake of approximately 10–12% DM.

As a general rule of thumb, avoiding early or first cut lucerne hays or harvested under drought stress can help reduce the risk of higher sugar levels. 

From an insulin standpoint alone, lucerne is generally considered a low-risk forage for horses with insulin dysregulation or insulin-associated laminitis. However, as with any forage, this is best confirmed through hay analysis, as individual samples can vary.

This is where much of the confusion begins:

While elevated insulin is the driver of metabolic disease in horses, insulin response is only one part of the picture. Low simple sugars and starch support insulin control, but they do not, on their own, determine whether lucerne is suitable for a given metabolic horse.

Energy Density: When Digestible Energy (DE) Becomes the Issue

Lucerne is more energy-dense than most grass hays.

When energy or “energy density” is discussed in relation to lucerne, it is often assumed that this refers to sugar. In lucerne, this is not the case as discussed above.

The majority of lucerne’s energy comes from digestible fibre and fermentable structural carbohydrates, which are broken down by microbes in the hindgut to produce volatile fatty acids (VFAs). These VFAs are a major energy source for the horse but do not cause a rise in blood glucose or insulin.

This is the same principle by which feeds such as beet pulp can provide significant energy while remaining low in sugar and starch.

For metabolic horses, the issue is not that lucerne’s energy is “unsafe”, but that total calorie intake still matters. Even energy derived from fibre can contribute to weight gain or difficulty losing weight if intake exceeds requirements, and increased adiposity is a key driver of reduced insulin sensitivity.

In other words, lucerne’s energy is metabolically different from sugar, but it is not calorie-neutral.

Protein: Not Harmful, but Not Always Neutral

Lucerne is also relatively high in crude protein, often ranging from 18–22% or more.

Protein itself does not raise insulin, and high-quality protein is valuable for:

• muscle maintenance

• topline support

• older horses 

• those needing additional high-quality protein to support muscle and topline

However, in some metabolic horses:

• total protein intake may already be adequate or excessive

• additional protein increases nitrogen load and excretion demands

• some horses appear less settled or less efficient on very high-protein rations

So while protein does not directly worsen insulin dysregulation, it still contributes to total dietary load and metabolic processing.

This is not about protein being “bad” – it’s about appropriateness for the individual horse and the rest of the diet.

When Lucerne Can Be a Good Choice

Lucerne may be helpful for metabolic horses that:

• have insulin dysregulation but poor topline or muscle loss

• are older or struggling to maintain condition

• are on very low-energy grass hay and need added nutritional support

• benefit from lucerne as a partial forage or ration component

In these cases, lucerne is often most effective when used strategically, rather than as the sole forage.

When Lucerne May Not Be Ideal

Lucerne may be less appropriate when:

• weight loss is the primary goal

• the horse is already overweight or obese

• protein requirements are already met

• lucerne displaces lower-energy forage in the diet

Again, this does not make lucerne unsafe – it simply means it may not align with the current management goal.

Considering the Inclusion Level

Another common source of confusion is how lucerne is substituted in the ration.

Lucerne is often introduced by replacing a grass hay on a weight-for-weight or volume-for-volume basis. Because lucerne is more energy-dense than most grass hays, this can inadvertently increase total calorie intake.

In many cases this is intentional with lucerne commonly added to support weight gain, topline, or muscle maintenance. However, when total energy intake exceeds the horse’s requirements, the horse will often “show it” through weight gain, difficulty losing condition or increased excitability.

For this reason, a useful rule of thumb is that lucerne is often best fed as a reduced proportion of the total forage ration, rather than as a direct one-for-one replacement for grass hay.

The Takeaway

Lucerne is not “good” or “bad” for metabolic horses.

While lucerne is typically low in simple sugars and starch, occasional samples can test higher, particularly early, first cut or drought stressed hays – reinforcing the value of forage analysis. Where testing isn’t feasible, avoiding the aforementioned hay types or using a short soak (around 15 minutes) as outlined in the previous post, can be a practical risk-reduction strategy.

From an insulin perspective, lucerne is generally a low-risk forage when appropriately selected. However, it is also nutrient-dense, energy-rich and high in quality protein, which means suitability depends on the individual horse and the overall diet.

Lucerne can therefore be either helpful or counterproductive, depending on the horse, the rest of the diet and the current management goal.

As with all metabolic management, the answer lies in context, testing and individualisation, not blanket rules. Working with an equine nutritionist can help ensure lucerne is used appropriately within a balanced and individualised feeding plan.