Quick Summary for Farmers: What You Need to Know About Lignin in Ryegrass

10 Feb

What is Lignin?

Lignin is a natural, tough substance in ryegrass that gives the plant strength and helps it stand up. It’s found mostly in the stems and acts like a barrier around the fibre inside the plant.

Why Does Lignin Matter?

Lignin cannot be digested by cows and sheep.
It blocks neutral detergent fibre (NDF) — the fibre cows and sheep can break down for energy.
More lignin means lower fibre digestibility, slower digestion, and less feed eaten.
If you have two ryegrasses with 40% NDF, they look the same on paper. However, if Variety A has 2% lignin and Variety B has 5% lignin, Variety A has a much higher chance for the rumen microbes to get inside and ferment the cellulose.
A lower percentage of lignin within the NDF doesn't just mean more of the fiber gets digested eventually—it means it gets digested faster.
We mostly measure quality by Metabolizable Energy (ME). A ryegrass with a low lignin-to-NDF ratio will consistently deliver a higher ME because the animal is extracting more energy out of every mouthful of fiber.

What is Neutral Detergent Fibre (NDF)?

NDF is the total fibre in pasture — made up of cellulose, hemicellulose, and lignin. The digestible parts are cellulose and hemicellulose, but lignin is indigestible and limits access to those.

If you want to identify the highest quality ryegrass, you are looking for the lowest ratio of lignin to NDF.

How Does Lignin Affect Animal Performance?

How does lignin slow rumen digestion and limit intake?

High lignin = slower fibre digestion and less energy from pasture.
This can limit how much animals eat (called rumen fill limitation), reducing milk production or liveweight gain.
Leafy ryegrass has less lignin and is more digestible than stemmy, mature ryegrass.

Practical Tips to Improve Pasture Utilisation

Choose ryegrass varieties bred for lower lignin impact and higher fibre digestibility — like Stride perennial ryegrass.
Manage grazing to avoid letting ryegrass become stemmy or flower, which increases lignin levels.
Aim for leafy pastures to keep intake and animal performance high.
Understand that small improvements in fibre digestibility can lead to big gains in animal productivity.
Keep reading below for a detailed explanation of lignin, how it affects fibre digestion and intake, and how modern breeding targets improved pasture quality.

Lignin in Ryegrass: Digestibility, NDF, Intake and the Breeding Focus Behind Stride Perennial Ryegrass

Ryegrass underpins New Zealand’s pasture‑based farming systems, supplying the majority of metabolizable energy for dairy, sheep and beef production. While pasture discussions often focus on dry matter yield, metabolizable energy (ME), crude protein, sugars and fiber, one component exerts a disproportionate influence on animal performance but is frequently overlooked: lignin.

This article provides a technical, nutrition‑focused explanation of lignin in ryegrass, its role in plant structure, how it influences neutral detergent fiber digestibility (NDFD), rate of digestion (kd), rumen fill and voluntary intake, and how modern breeding—such as the approach used in Stride perennial ryegrass—targets improved utilization rather than yield alone.

What Is Lignin?

Lignin is a complex; indigestible phenolic polymer embedded within plant cell walls. Its role is structural rather than nutritional.

In ryegrass, lignin:

Provides mechanical strength, allowing the plant to remain upright
Adds rigidity to stems
Contributes to water impermeability of cell walls
Provides protection against insects and physical damage

From a plant perspective, lignin is essential for persistence and survival. From an animal nutrition perspective, it is a necessary constraint, because lignin itself cannot be digested and limits access to digestible nutrients within the plant.

Where Lignin Sits in the Ryegrass Plant

Up to 60% of a ryegrass plant consists of cell wall material, compared with approximately 45% in modern maize hybrids. The ryegrass cell wall is composed of:

Cellulose
Hemicellulose
Lignin

Ruminants can digest cellulose and hemicellulose via microbial fermentation in the rumen. Lignin, however, is indigestible. More importantly, lignin forms cross‑linkages with cellulose and hemicellulose, physically enclosing digestible fiber and sugars.

A useful analogy is to think of lignin as a mechanical pulp surrounding the valuable energy inside the plant. The more complete this barrier, the slower and less complete fiber digestion becomes.

Why Lignin Is the Primary Limiter of Digestibility

Lignin is widely recognized as the single most important factor limiting fiber digestibility in grasses.

As lignin concentration and lignification increase:

Fibre digestibility declines
The rate of fibre digestion slows
Rumen retention time increases
Voluntary feed intake decreases
Animal performance (milk yield, liveweight gain, body condition) is reduced

These effects occur for two main reasons:

Physical restriction – lignin shields cellulose and hemicellulose from microbial attachment and enzymatic attack

2. Biochemical effects – lignin precursors can inhibit rumen microbial activity

The combined result is slower breakdown of fibre, earlier rumen fill, and intake limitation even when pasture supply is adequate.

Lignin Concentration and Its Effects

Lignin concentration in forages can range from approximately 2% to over 20% of dry matter, depending on species and stage of maturity.

Low lignin (≈2–4% of DM)

Typical of young, leafy ryegrass
Rapid rumen fibre degradation
High NDF digestibility
Faster access to sugars, protein and minerals
High voluntary intake
Efficient conversion to milk or liveweight gain

Moderate lignin (5–8% of DM)

Characteristic of well‑managed, vegetative pasture
Balanced structural integrity and digestibility
Suitable for most grazing systems
Supports strong production without excessive rumen fill

High lignin (>8–10% of DM)

Common in stemmy or reproductive pasture, and high lignin species
Slow fibre digestion
Reduced intake due to rumen fill limitation
Lower ME extraction per kg of dry matter
Noticeable decline in animal performance

At high levels, lignin can become a hard biological limit on production, regardless of pasture cover.

Ryegrass Maturity and Lignin

In ryegrass, lignin is:

More prevalent in stems than leaves
Strongly associated with reproductive development

Research shows lignin concentration does not always increase linearly during early vegetative growth (for example, around 50–60 days of regrowth). However, once ryegrass enters stem elongation and flowering, digestibility and intake decline rapidly.

This underpins several well‑established principles of pasture management:

Leaf‑dominant pasture supports higher intake and production
Flowering pasture is associated with reduced animal performance
Grazing management has a major influence on effective lignin intake

Lignin, NDF Digestibility (NDFD) and Rate of Digestion (kd)

From a ruminant nutrition standpoint, lignin exerts its greatest effect through neutral detergent fibre digestibility (NDFD) and the rate constant of fibre digestion (kd).

Neutral detergent fibre represents the total structural carbohydrate fraction of the plant cell wall. Only a portion of NDF is potentially digestible, and lignin determines both:

The size of the digestible NDF pool
How accessible that pool is to rumen microbes

As lignin concentration and cross‑linking increase:

Potentially digestible NDF declines
Total NDFD decreases (e.g. at 24 h, 30 h and 48 h incubation)
The rate of digestion (kd) slows

Fibre with a lower kd remains in the rumen for longer, increasing rumen retention time and contributing directly to rumen fill limitation.

Rumen Fill, Intake and Energy Supply

As fibre digestion slows, undigested NDF accumulates in the rumen. In high‑producing animals—particularly dairy cows grazing ryegrass‑based pastures—rumen capacity becomes the dominant constraint on intake.

Ryegrass with a lower effective lignin barrier is characterized by:

Higher NDFD
Faster microbial colonization of fibre particles
Increased kd of NDF digestion
More rapid particle size reduction and rumen clearance

Improved rumen turnover reduces physical fill constraints, allowing higher voluntary dry matter intake without compromising rumen function.

From an energy perspective, improvements in NDFD and kd increase metabolizable energy yield per kilogram of dry matter, even when total NDF concentration remains unchanged. Faster fibre digestion also improves synchrony between fermentable carbohydrates and rumen nitrogen supply, supporting microbial protein synthesis and feed efficiency.

Measuring Lignin in Ryegrass

Lignin is typically quantified using the Acid Detergent Lignin (ADL) method, which isolates lignin after sequential removal of hemicellulose and cellulose.

Because lignin is highly insoluble and extensively cross‑linked, direct measurement is complex. Advances in Near Infra‑Red Spectroscopy (NIRS) now allow rapid estimation of lignin and fibre digestibility parameters as part of routine forage analysis.

These measurements are increasingly used for:

Forage quality assessment
Ration formulation
Predicting animal intake and performance

Lignin Structure Matters – Not Just Quantity

Modern forage breeding has demonstrated that lignin structure and organisation within the cell wall can be as important as total lignin concentration.

In conventional ryegrass types, lignin forms dense, restrictive associations with cellulose and hemicellulose. In contrast, advanced perennial ryegrass breeding focuses on:

Optimizing lignin composition
Reducing restrictive cross‑linking
Improving accessibility of digestible fibre to rumen microbes

The outcome is:

Faster cell wall breakdown
Improved NDF digestibility
Greater energy extraction from the same dry matter yield

This shift represents a move from breeding purely for yield toward breeding for utilization efficiency.

What This Means for Stride Perennial Ryegrass

The breeding focus behind Stride perennial ryegrass reflects these principles. Rather than targeting yield alone, Stride has been selected to support:

High fibre digestibility
Faster rumen fibre degradation
Improved intake potential under grazing
Efficient conversion of pasture into animal performance

By improving how fibre is utilized—through effective management of lignin’s impact—Stride aims to lift metabolizable energy intake per hectare, not just dry matter grown.

Practical Take‑Home Messages

Lignin is essential for plant structure but limits animal performance
Higher lignin reduces NDF digestibility, slows kd and restricts intake
Leafy ryegrass has lower effective lignin impact than stemmy pasture
Grazing management that avoids heading improves utilization
Variety selection matters: digestibility is as important as yield
Small improvements in lignin accessibility can deliver large gains in intake and production

Final Thoughts

Pasture quantity will always matter, but pasture quality drives performance. Lignin sits at the center of the quality equation in ryegrass‑based systems.

By understanding how lignin interacts with fibre digestion, rumen kinetics and intake, farmers and advisors can make more informed decisions around grazing management, pasture renewal and ryegrass selection.

In pasture‑based systems, improving digestibility is often the most cost‑effective way to lift production. Managing lignin—through both management and breeding—is a key part of that strategy.

Don't just look at the total Fiber (NDF). Look at the Lignin. The less lignin there is holding that fiber together, the faster the cow can break it down, the more she can eat, and the more milk or meat you'll put in the tank/on the scales.

Tips on how to Read Your Lab Report: For the High Octane Check

When you get a pasture or silage test back, don’t just look at the ME (Metabolisable Energy). Check these metrics to see how much of that energy your stock can actually unlock.

NDF (Neutral Detergent Fibre): The Bulk factor.

Goal: 35% – 45% for high-producing cows.

What it means: High NDF (above 50%) acts like a speed limiter in the rumen, making the animal feel full before they’ve eaten enough energy.

Lignin (or ADL - Acid Detergent Lignin): The Indigestible Lock.

Goal: As low as possible (typically <4% in high-quality leafy ryegrass).

What it means: This is the 100% indigestible part. If this number is climbing, your pasture could be getting woody and the fiber is becoming harder to crack, or it could be just a high Ligin variety of pasture.

NDFD (NDF Digestibility): The Efficiency score.

Goal: >70% (Excellent).

What it means: This tells you what percentage of the fiber is actually usable. A high NDFD means the plant has a low lignin barrier.

kd (Rate of Digestion): The Throughput speed.

Goal: Look for a higher percentage per hour (e.g., 5-8%/hr for fiber).

What it means: This is the secret to high production. The faster the kd, the quicker the cow clears her rumen and heads back to the break for another feed.

Farmer’s Rule of Thumb:

If your NDF is high and your Lignin is high, you've missed the grazing window, or you may not have a low Lignin variety, or the grass is stemmy, the rate of digestion (kd) has slowed down, and your milk or meat production will likely drop because the animals simply can't process enough bulk.