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Ryegrass varieties Ploidy Endophyte Heading date High sugar grasses Persistency problems Survival factors Biology of ryegrass Nutrients in Ryegrass

Ryegrass selection for a dairy farm system involves key decisions: choosing the right ryegrass variety (from annual to perennial), picking an endophyte for insect control, and selecting ploidy (diploid or tetraploid) and a heading date. Ryegrass varieties differ in persistence; for instance, annual ryegrass lasts less than a year, while perennial can persist for 5 years or more. Ploidy relates to the number of chromosomes a plant has. Diploids are robust and tetraploids are more palatable but require more management. Endophytes are fungi in ryegrass that offer protection against insects but can affect animal health. Heading date indicates when seedheads emerge, impacting feed quality. Lastly, high sugar grasses, with more water-soluble carbohydrates, offer varied benefits, but the relationship between higher sugar content and milk production isn't direct.

Which ryegrass cultivator will work for my farm?

When selecting a ryegrass cultivar to match a specific farm system, key decisions include...

  • Ryegrass variety - perennial, short rotation, Italian or annual
  • Endophyte choice - insect control, performance and persistence
  • Ploidy choice - diploid or tetraploid cultivar
  • Heading date - early, mid or late.

Ryegrass varieties

Ryegrass varies from the most persistent (perennial ryegrass) to the least persistent (annual ryegrass) and can be broadly categorised by how long they live or persist.

Annual - Less than one year

Italian - 1-2 years

Short rotation - 2-5 years

Perennial - 5 years

Annual and Italian ryegrass

These two ryegrass species are described together because they are used in similar situations, for their fast establishment and high winter - early spring DM yield.

Annual and Italian ryegrasses both establish very quickly and in good conditions are typically ready for a first light grazing 4-6 weeks after sowing, up to 2 weeks sooner than a perennial ryegrass.

When sown in March as a winter crop, annual and Italian ryegrasses produce a similar amount, normally 7-8 t DM/ha over 6-8 months.

Annual ryegrass is less persistent and is most commonly autumn sown as a 6-8 month winter/spring crop. In summer moist areas with low insect pressures it can persist for 1-2 years.

Italian ryegrasses typically last 12-18 months in drier areas, and 3 or more years under mild summer conditions. Some recent Italian ryegrasses have endophyte so may persist a year longer than those without, depending upon the pests present.

Italian ryegrasses keep growing into summer, and over a 12 month period typically produce 15 t DM/ha, However, this figure varies widely with yields of 20 t DM/ha measured in summer wet or irrigated conditions, whereas in very dry summer conditions yields have been as low as 10 t DM/ha).

Including Italian or annual ryegrass in a permanent pasture seed mix is not generally recommended. They will die out, allowing weeds to take over. In the northern northland annual ryegrass is a suitable host for black beetle.

Short rotation (hybrid) ryegrass

Short rotation or hybrid ryegrasses are generally derived from crossing perennial ryegrass and Italian ryegrass. Cultivars vary, but typically persist from 2-5 years, depending on conditions.

Their feed quality and winter growth is very good, generally a little higher than perennial ryegrass in similar circumstances.

Many cultivars contain endophyte which improves their persistence.

The total DM yield of short rotation ryegrasses is similar, or higher, than perennial ryegrass over a 12 month period. The major difference however is the cool season production, which is typically higher.

Summer feed quality is influenced by aftermath heading (or seeding), and potential summer growth varies between cultivars.

Short rotation ryegrasses are used in several ways including:

  • As a short term pasture, where a paddock is destined to go into crop in 2-5 years.
  • For undersowing into thin pasture to improve its growth for 2-3 years.
  • Added to perennial pasture seed mixtures to provide increased winter production during the first few years and to boost animal performance in cooler regions.

Perennial ryegrass

Perennial ryegrass is the most widely sown grass in New Zealand as it grows well in a wide range of conditions; is easy to establish and manage; provides high animal performance; generally has good persistence and forms a compatible mix with white clover.

Production of perennial ryegrass-based pastures on dairy farms average 14 t DM/ha/year in New Zealand, with yields over 20 t DM/ha/year achieved under irrigation.

In summer moist environments with good management perennial ryegrass pastures can last indefinitely.

Where summer dry conditions and significant pest pressure prevail, a more realistic expectation of persistence may be less than 10 years. Pasture management is a key determining factor, so persistence varies widely in these situations.


Ploidy refers to the number of chromosomes per cell in a plant, a diploid ryegrass has two sets of chromosomes while a tetraploid ryegrass has four sets. These differences create differing plant characteristics with associated advantages and disadvantages for each type.


Diploid plants have more tillers per plant and, due to the lower water content per cell, have a higher dry matter per kilogram of feed and more energy than tetraploid plants. Both varieties have similar protein levels.

Recommended in higher stocking rate systems where overgrazing and pugging may occur


  • Robust - less likely to be overgrazed and attacked by argentine stem weevil, and more tolerant to pugging Harder to overgrazed
  • Less attacked by Argentine stem weevil
  • More tolerant to pugging


  • Lower metabolisable energy - lower ratio of soluble carbohydrates to fibre
  • Less clover friendly - lower, denser growth habit can shade clover


Tetraploids are more palatable, are preferred by grazing animals, and have been shown to improve milksolids production by up to 7%.  However, tetraploid ryegrasses are less robust and require more careful management under stressful conditions.

Because of the extra chromosomes, tetraploids have a bigger cell size and have a higher ratio of cell contents (soluble carbohydrates) to cell wall (fibre), indicating that they have a higher water content per cell.

Recommended in systems with high performance management, particularly where looking to increase per cow performance.


  • Higher metabolisable energy, more palatable to stock, easier to digest
  • Better utilisation (easier to graze to good residuals)
  • Clover friendly - open, erect growth habit promotes more clover
  • Less facial eczema spores (as better grazed)


  • More prone to over grazing
  • Require careful management in wet and drought conditions
  • Preferred by Argentine stem weevil


An endophyte is a naturally occurring fungus that is found in ryegrass and tall fescue pastures. They are essential for persistence in most New Zealand pastures.

The endophyte protects plants from a range of insects but can be associated with animal health problems, especially ryegrass staggers. There are different types of endophyte and each varies in persistence, yield, and insect protection.

Heading date

A heading date is when 50% of the plants have emerged seedheads. Heading date is an important consideration as seedhead development reduces feed quality in late spring and heading date determines when this occurs.

Heading dates are defined relative to the cultivar Nui (approximately 22 October), heading at day 0.

Heading date definition Days relative to Nui
Nui 0
Early-season -21 to -8
Mid-season -7 to +7
Late-season +8 to +21
Very late-season +22 days or later
  • Early heading date (up to about +7 days) means better early spring growth
  • Late heading date means better late spring and summer feed quality.

Heading dates vary between ryegrasses, and these should be understood to ensure the cultivar mix on a farm is most appropriate to its pasture production requirements and soil characteristics.

Late and very late heading cultivars provide a significant advantage in late spring quality, so make pasture management easier, and help maintain the cows pasture intake through this period.

Do not mix early and late heading cultivars in the same paddock as:

  • The higher feed quality of late heading paddocks in late spring is diluted
  • It is easier to strategically graze or mow to control seeding of a pasture with a more uniform heading date.

Sow no more than 50% of the farm in late or very late cultivars to minimise early spring feed pinches.

High sugar grasses

High sugar grasses are diploid perennial ryegrass bred for elevated levels of water soluble carbohydrates (WSC).

These grasses have a larger proportion of their ME (metabolisable energy) as plant sugars which are readily fermentable in the rumen. There are now New Zealand-bred varieties available such as Expo with the high sugar trait. High WSC levels can also be found in many tetraploid ryegrasses.

There has been considerable research and debate about water soluble carbohydrate, with a review of 21 animal experiments concluded that there was no consistent response of intake, milk yield or liveweight gain to feeding high WSC pastures.

New Zealand trials on early HSG grasses found the expression of the trait (elevated WSC) was enhanced after a sustained period of cold weather and short days. A ‘gene x environment interaction’ was shown to exist in the expression of the HSG trait which could impact on the performance of plants containing the gene under NZ conditions as previous research was completed in the UK.

Research at Massey University showed that in spring there was no difference among ryegrass varieties in the yields of MS. In autumn, yields from cows fed both high WSC grasses (HSG and IRG) were significantly higher than from the control perennial ryegrass (STG). MS yield from cows fed HSG did not differ significantly from the cows fed tetraploid Italian ryegrass.

The WSC concentrations differed significantly among grasses in spring, but not in autumn. Furthermore, the overall concentrations of WSC are higher in spring than they are in autumn. Thus it is not possible to establish a direct relationship between higher WSC and increased MS production.

Persistency problems

Poor persistence commonly refers to the loss of plants leading to the invasion of weeds and reduced productivity.

Ryegrass populations

  • A perennial ryegrass pasture is a population of tens of thousands of plants, and literally millions of tillers, per hectare.
  • When a new pasture is sown (e.g. 20kg seed/hectare), about 9 million seeds are planted per hectare. Because perennial ryegrass is an out-crossing species, each seed carries a slightly different combination of genes.
  • Subsequently, the soil, weather and management conditions imposed on the pasture, will drive this genetic diversity. As a result, certain seeds/seedlings/plants will survive, while others will not.
  • During the first year, the plants that lack the characteristics needed to survive in the pasture are eliminated, leaving the stronger ones. New pastures need nurturing to get through their first 12 months in good shape to produce again. Read more about managing new pastures here.
  • After the first year, the original plants start to break-up into smaller plants which are just groups of connected tillers, each with some root material. From this point on, the pasture comprises about 50 million tillers per hectare, each producing the leaves which generate the pasture growth for animal feed.

A newly-sown ryegrass pasture with about 4 million seedlings per hectare. Each seedling has a unique combination of genes.

A healthy ryegrass plant with several tillers about 12 months after sowing. From this point, the objective is to maximise the survival of the approximately 50 million tillers per hectare that make up the pasture.

What is perennial ryegrass?

  • Perennial ryegrass evolved in cooler wetter climates of north-west Europe, therefore it likes soil moisture in summer, cooler night temperatures (below 20°C) and soil fertility (especially N).
  • Natural growth habit is to keep growing new leaves regardless of the conditions – this is a good strategy to compete with other species for light and makes it a productive feed for cows.
  • When ryegrass is grazed it will put lots of energy into new leaf production, before conserving energy or growing a root system. This is okay if the interval between grazing is long enough for the plant to rebuild leaf area, grow tillers and catch up with root and reserve maintenance. For more information see The ryegrass plant page.
  • If the ryegrass is grazed too early then the plant won’t store energy reserves, grow new tillers or under lots of pressure maintain its root system. For more information see the Leaf stage page.
  • If a ryegrass pasture is exposed to multiple stresses such as this overgrazing, combined with stresses such as drought or insect attack, then ryegrass pastures can fail.
  • The longest period an individual tiller can survive is 12 months. The survival of pasture then depends on new tillers. If the plant suffers a severe shortage of energy, then it may not produce new tillers. If not enough new tillers (daughter tillers) survive to replace the existing parent tillers, then the ryegrass pasture will fail.

Survival factors

Poor physical survival of ryegrass populations are often due to multiple, overlapping factors which kill the tillers. These are the most important factors:

Biology of ryegrass

Want more high quality pasture? Get to know the biology of ryegrass and learn the finer points on how to grow it well.

  • A perennial ryegrass pasture is made up of a population of individual plants, each plant is made up of a number of tillers.
  • Each tiller can only maintain 3 live leaves. Each leaf will develop from the growing point at the base of the tiller.
  • Ryegrass growing point is at the base of the plant where it is not damaged from grazing.
  • Each tiller is capable of producing new or daughter tillers. These daughter tillers produce a new plant.

Identifying perennial ryegrass

  • Leaves: hairless, defined mid-rib, ribbed on upper surface, shiny underneath
  • The emerging leaf is folded
  • Reddish /purple base (Dead leaf material may need to be peeled back to see this)
  • Plants are made up of a number of tillers
  • Each tiller:
    • has its own leaves and roots
    • maintains three live leaves which develop from the growing point at the base of the tiller
    • is capable of producing new or daughter tillers
    • has one leaf growing at a time
    • as the fourth new leaf emerges, the oldest leaf dies
    • lives for about one year
  • Spring and autumn are key periods of tillering - production/growth of new tillers
  • Tillers can be classified as vegetative (leafy) or reproductive
  • A reproductive tiller can be identified by looking for, or feeling for, nodes on the stem
  • When tillers become reproductive the stem elongates and eventually, if the tiller is not grazed, a seed-head is produced
  • Poa and Italian ryegrass are commonly mistaken for perennial ryegrass.

Sunlight provides the basic food for ryegrass plants. Light energy is captured and used by leaves for photosynthesis, providing energy for plant growth.

Grazing or harvesting pasture removes the ryegrass leaves and deprives the plant of light energy, the plants primary food source.

However, ryegrass leaves have a limited lifespan regardless of grazing. Ryegrass is termed a ‘three leaf plant’ because each tiller generally sustains a maximum of three live leaves.

There is always only one leaf growing in each tiller at any time, when the next leaf appears, the previous leaf has stopped growing.

How quickly do leaves grow?

The time it takes for a tiller to produce a new leaf is largely dependent on temperature and moisture. Ryegrass grows best in the range 5°-18 °C. In mid-spring a new leaf may grow every 8 days while in mid-winter this time will increase significantly.

Read more about leaf emergence rates here.

A ryegrass tiller has a growing point from which new leaves grow. The growing point is found at the base of the tiller, close to the soil surface where it won’t be damaged during grazing, allowing the tiller to regrow.

Perennial ryegrasses mainly reproduce through daughter tillers which become separated from the parent tiller and result in a new plant.

Each tiller must leave behind one offspring. Few new ryegrass plants emerge in established pasture through seed germination under existing management.  The perennial nature of ryegrass depends on tillering as a tiller only lives for one year.

Spring and Autumn are key periods of tillering. Every time a new leaf is produced, a new tiller bud is produced. It stays dormant until the right conditions come for it to grow.

Autumn tillers are the one that will grow your winter and summer pastures. The spring tillers will grow your spring, summer, and autumn pastures.

What does this mean for grazing management and nutrition?

  • The live ryegrass leaf is the nutritious and most easily digestible part of the plant. It is easily digested by the cow and can therefore sustain high levels of milksolids. For more information on the nutritional value of ryegrass see the Ryegrass as a feed section.
  • The aim of grazing management is to optimize the amount of live leaf available to the cow by grazing at the 2.5 to 3 leaf stage. This maximises the capture of sunlight and optimizes pasture quality.
  • Monitoring leaf stage is an effective indicator of when a paddock is ready to graze. For more information, leaf emergence rates see the Leaf stage page.
  • Good grazing management in spring promotes tillering:
  • Grazing management is key to the survival of daughter tillers. New daughter tillers born in spring need as much light as possible to develop.
  • Daughter tillers will not survive weeks of darkness under high pasture covers. consistent grazing residuals of 1500-1600 kg DM/ha will enable sun light to reach the base of the pasture and help the survival of newly emerged daughter tillers.

Grazing too early?

Grazing before the 2.5 leaves per tiller reduces yield and regrowth as it does not allow the plants reserves to be fully restored.

Grazing too late?

If a pasture grows too long (>3500 kg DM/ha) it produces new leaves and the old leaves die, these dying leave accumulate in the base of the pasture leading to:

  • Reduced pasture ME – dead material
  • Increased disease (favourable environment for pests, diseases, fungal spores)
  • Decreased pasture utilisation
  • Reduced clover content due to shading.

Grazing too low?

Grazing too low can reduce regrowth as less leaf material is left to help regrowth and stem material is reduced.  Graze to the same height each time e.g. if residual is set to 1500kgDM stick to it.

Nutrients in Ryegrass

High quality ryegrass pastures meet the nutritional requirements of the dairy cow. Dairy cows are ruminants, and have evolved to thrive on forages.

Microbes in the rumen enable the cow to digest plant material, therefore cows are very efficient at extracting energy from forages such as pasture.

Many of the nutritional recommendations widely provided are based on data derived from cows fed a total mixed ration (TMR) but these are not always applicable to grazing dairy cows. This is because pasture and pasture-fed cows have unique characteristics:

Carbohydrates (sugars)

In theory, milk production is maximised when soluble sugars and starches are 35-40% of the diet. Although spring pasture contains less than this, the structural carbohydrates (cellulose) in good quality, leafy pastures are highly digestible (70-85%) and are degraded relatively quickly, thus supplying similar energy to soluble sugars and starches. This means there is enough readily available energy in pasture for the dairy cow.

But why?

This is because the building blocks of all carbohydrates (soluble sugars and starches, and structural carbohydrates) are essentially the same (a simple sugar e.g. glucose) with the only chemical difference being the type of bonds that joins the sugar molecules. Bugs in the rumen can break all these bonds supplying the pasture-fed cows with energy.


Recommendations from total mixed rations suggest that neutral detergent fibre (NDF) should make up 27-33% dry matter intake with effective fibre (the fibre most effective at stimulating rumination and salivation) making up 20% of dry matter intake.

The neutral detergent fibre (NDF) content of pastures is generally in excess of these requirements and although the ‘effective’ fibre in pasture is estimated to be lower (17-20% DM) than a TMR diet (and rumen pH are sometimes lower than recommended), this does not negatively affect digestion or microbial growth. Further there are no performance benefits of adding additional effective fibre (for example straw or hay) to a pasture-based diet.

But why?

This is because the lower rumen pH in pasture-fed cows is generally caused by an increase in acetic acid (such as vinegar) and does not result in rumen upset. In comparison, a drop in rumen pH in a TMR-fed cow is usually associated with increased lactic acid which can have detrimental effects (rumen acidosis, lameness).

Additionally, it is sometimes suggested that if the NDF content of the diet is too high, dry matter intake will be limited and occasionally the below equation is used to predict intake:

Dry matter intake = (120 ÷ NDF%) ÷ 100 x liveweight

However, this would suggest a 500 kg cow eating pasture at 40% NDF can only eat 15 kg DM or produce 1.5 kg MS which is not true.  In reality, a 500 kg cow eating good quality pasture with an NDF of 40 – 45% will still eat 17 -20 kg DM and produce 2 kg MS. In fact, when cows are grazing good quality pastures NDF content has only a very small impact on intake.

This is because the NDF in good quality pastures is highly digestible and rapidly degraded.  However, as pasture quality declines, and digestibility and degradation rate decrease, NDF will play a bigger role in regulating intake.

Thus the fibre in poor quality hay, silages or ryegrass that has not been managed properly, or in some tropical grasses (kikuyu) can play a role in limiting intake.


Recommended protein levels for TMR- fed cows in early lactation, is a diet containing about 18% crude protein, of which 65% is degradable, while 35% is not digested in the rumen (by-pass protein).

At most times, good quality pasture contains more protein than cows require. Even though the protein in pasture is highly degradable (70-90%), fast rumen passage rate means there is still sufficient dietary protein that by-passes the rumen.

But why?

When protein is degraded in the rumen, ammonia is produced and is used by the rumen microorganisms for their own growth. Any excess ammonia is transported in the blood to the liver, where it is converted to urea and either excreted: primarily via urine, although a small amount ends up in milk, or recycled back to the rumen.

The process of converting ammonia to urea is not energetically expensive to the dairy cow and in pasture-based systems, high dietary intakes of crude protein are not detrimental to health or reproduction.

Wait a sec, Milk urea?

Milk urea is a by-product of the breakdown of dietary protein in the rumen, and, it is an approximate indicator of dietary protein. Briefly, in a pasture based system, high MU levels are not detrimental to performance or reproduction, and generally it is not economical to bring in protein supplements if MU levels are low. For more information, see the Milk urea page.

Can milk urea concentrations help to improve environmental footprint?

Although milk urea concentrations are positively associated with urinary nitrogen concentrations, the implications of small changes in the urinary nitrogen concentration on environmental nitrogen loading needs to be considered with other system factors.

Numerous management and resource factors determine the environmental outcome on farm and the impact of any change must be determined by considering the whole farm system (e.g. stocking rate and dry matter intake). The addition of low protein supplement to reduce milk urea and subsequent intensification in the absence of changes in other inputs, management practices or infrastructure, could lead to increased nitrogen leaching per hectare.

Last updated: Sep 2023

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