The nutritional value of grass guide (2024)

Grass is by far the cheapest forage available, and the better you manage it, the cheaper you can grow it. Grass also adds value to Irish agriculture by helping to portray the clean, green image associated with Irish animal food production.

To get the most out of grass, livestock farmers must manage the grass all year round to optimize the balance between grass supply and demand. Livestock producers must also ensure that sufficient quantities of silage are stored to provide adequate feed for the animals when housed.

With this guide we want to help livestock farmers gain a better insight into the nutritional composition of grass. We provide simple definitions and emphasize the importance of different components for maximum livestock performance. We also provide tips on how to get the best performance from your department.

Although effective as a standalone crop, grass is also often grown with white clover as a companion crop. Where relevant, we will also highlight the nutritional contribution of white clover.

Contents

1. drug matter
2. Grass quality
3. Water soluble carbohydrates
4. Egg white
5. Grass fiber
6. lipids (oil)
7. Minerals and vitamins in grass

drug matter

Why is dry matter in grass important?

The dry matter content (DM) of grass and forage is measured as a percentage and represents the proportion of total components (fiber, protein, ash, water-soluble carbohydrates, lipids, etc.) remaining after the water is removed.

It is important to know the dry matter percentage of grass and roughage. The lower the dry matter content of grass, the higher the fresh weight of the feed required to achieve targeted nutrient absorption, regardless of whether it is grazing grass or canned feed.

DM is also used as a term to measure yield. This is recorded as kg DM/ha and is used as a measure of grass carrying capacity (stocking rate) and is an essential element for effective grazing management. It is also used to measure the yield of silage crops.

Requirements for fresh grass at different DM contents

The range of dry matter in grass

In terms of dry matter content, field and weather conditions will cause significant variations, and there are also inherent differences between diploid and tetraploid grasses. All other factors being equal, diploids have a higher dry matter content (typically 2% higher) than tetraploids because diploids have smaller cells and a lower cell wall to cell volume ratio.

This means that ruminants fed exclusively on a tetraploid pasture must consume more fresh grass per day to achieve the same nutritional intake as from a purely diploid pasture.

Looking at the dry matter yield, modern ryegrass has been bred for maximum production. The top rated perennial ryegrass varieties on the recommended list are now able to graze or maintain yields of more than 14 tonnes DM/ha, while weedy grasses (e.g.

Ryegrass production over a season follows the classic growth curve, peaking at approximately 120 kg DM/ha per season. day in May and typically drops to about one-third of peak levels in early fall.

Get the most out of dry matter

In terms of grazing, the goal should be to provide a pasture that provides the ideal balance of fresh, nutrient-rich growth with sufficient fiber content for optimal rumen passage. This balance is best achieved by using a grazing rotation of 18-21 days during the high season.
Poor management of grasslands will increase the proportion of dead and dying plant material, resulting in a significant reduction in forage quality and absorption potential.

When producing silage, the aim should be a reduction of 16-20% dry matter and an ensiling percentage of 30-35% (for compact silage) and 35-40% (bale). This ensures good fermentation and optimal absorption and a minimal risk of aerobic instability.

Seasonal grass production

Increased grass production during the season (in spring and again in autumn) has the potential to improve farm profitability due to the reduced need to purchase more expensive feed such as concentrates and reduce dependence on silage.

Grass growth depends on soil temperatures above 6°C, while clover requires temperatures above 8°C. In Ireland we typically have very low grass growth in the spring and again in the autumn due to the climate. The maximum growth rates are reached in May.

While there is little we can do about the weather in the spring and fall, there are steps we can take to improve grass production over the course of the season.

Dry dust guide

• Use seasonal and total DM yield values ​​when selecting the best varieties from the Irish recommended list
• Keep in mind that animals on wet pastures need to consume more fresh feed per day
• Delayed cutting for silage increases yield but reduces quality

The clover effect: DM

The total DM yield from a grass and clover field with an optimal white clover content is broadly compatible with a straight ryegrass sword, assuming an average Irish nitrogen fertilization.

Grass quality

What is digestibility (D value)?

The quality of grazed grass is described by the digestibility value (D value). Digestibility is the part of the feed that can potentially be digested by a ruminant. The digestible part of the feed consists of a combination of crude protein (CP), carbohydrates (including digestible fibers and sugars) and lipids (oils).

The digestibility of grazed grass

Grass digestibility is highest when a lawn contains fresh leaf growth and decreases as the plants mature (stems). From May to June, when the grass begins to become reproductive (seed heads appear), digestibility can be reduced to as low as 67%. The highest ranked breeds on the recommended list will be higher at 72-75%.

Sedges managed within a rotational grazing period of 18 to 25 days will have a higher D value, typically between 74 and 77%, with the highest ranked breeds having a similar value of 77 to 80%. Weed grasses will have a significantly lower D-value than modern ryegrasses.

What is metabolizable energy (ME)?

Metabolizable energy (ME) is the energy that an animal can obtain from food. ME is measured in megajoules of energy per kg of dry matter (MJ/kg DM). It is directly related to digestibility, because any feed must be digestible before the energy is available.

One percentage point of the D value corresponds to 0.16 MJ/kg DM ME.

Maximize digestibility and metabolizable energy

The higher the D value that can be achieved, the better the performance of the ruminants will be in terms of milk production or growth rates. In Ireland, Teagasc estimates that a one unit increase in digestibility is equivalent to0.25 liters of milk per dairy cow per day.

Nutritional value of grass species

Bron:J. Frame, 1991

Nutrient content for agricultural feed

D value and ME pointer

• Choose the highest ranked varieties on the Irish recommended list
• Use a rotating paddock grazing system (18-25 days), with access determined by the 'Triple system'
• Consider the availability of soil nutrients and always apply best practices when applying fertilizer
• Cut for silage before stem thickening, or about a week before heading
• If necessary, graze the grass to prevent the grass from drifting

The clover effect: D value & ME

White and red cloverstypically have D values ​​similar to the top-ranked ryegrass varieties, with a greater portion of the digestible material being in the form of crude protein (e.g., lower carbohydrates).

The optimalwhite cloverthe content of a pasture averages 30% over a grazing season.

If includedred clover in one silageit is important to use compatible ryegrass varieties to obtain the best overall D-value when mowing. As with ryegrass, the D value of red clover drops rapidly as the crop matures. The goal is to mow when no more than half of the plants are in bud.

Water soluble carbohydrates

Why are water soluble carbohydrates (WSC) important in grass?

Water-soluble carbohydrates are the soluble sugars that quickly pass from the grass into the rumen. These sugars provide a readily available energy source for the rumen microbes responsible for the digestion of feed.

These sugars also provide fuel for silage fermentation. The higher the sugar content, the better the silage is preserved and the higher the nutritional value for the animal.

The selection of WSC in grass

Higher WSC is a key differentiator in modern ryegrass bred at IBERS Aberystwyth University over the past 30 years. Varieties with a higher WSC value than conventional varieties are now available asMonkeys tall sugar grass.

Relative differences in WSC persist among ryegrass cultivars, although contents typically rise and fall over a season, with varying weather conditions, and even over the course of a day. On a warm sunny summer day, WSC content can be as high as 35% of dry matter, while on a cool, cloudy fall day it can be as low as 10%, but differences between cultivars remain at both ends of the spectrum.

Get the most out of WSC

A high WSC will generally mean that the feed composition is closer to the 2:1 WSC/crude protein ratio, which animal models indicate is the target for optimal nitrogen use in the rumen. This means that more of the feed is converted into milk and meat, and less is wasted on urine (and methane). Under ideal growing conditions, modern Aber HSG ryegrass will achieve the optimal ratio of 2:1 for WSC protein.

Average WSC over five years

WSC directions

• Select and sow grass and silage mixtures with high digestibility and high WSC values
• Avoid excessive use of fertilizer by following best practice guidelines
• Cut for silage in late afternoon to maximize WSC content
• Avoid making silage that is too wet (below 28% DM), this can lead to sugar loss in the effluent and increase the amount of effluent (wet silage also has an increased need for sugars to create good fermentation and stable silage)
• WSC generally peaks three to five weeks after grazing or mowing

The clover effect: WSC

White clover generally contains less WSC and more protein than perennial ryegrass. For optimal performance it is therefore important to maintain the target of 30% white clover during a grazing season.

red clovergenerally has a lower WSC content than perennial ryegrass, so growing it in combination with high WSC grasses is beneficial for silage fermentation.

Egg white

Why are proteins in grass important?

Protein is a large and expensive part of the livestock ration, and dependence on imported sources (e.g. soy) makes companies vulnerable to fluctuations in price and supply. Greater use of home-grown proteins is therefore desirable.

Grass protein is generally reported as total crude protein (CP), which is 6.25 times the nitrogen content. Typically, about 80% of the crude protein in fresh grass is true protein. The remaining fraction is often referred to as non-protein nitrogen. Both types of nitrogen can be used by the animal, but true protein is used more efficiently for meat and milk production. A greater portion of the non-protein nitrogen is used inefficiently and excreted by the animal.

Crude protein can be divided into efficiently rumen degradable protein (ERDP) and digestible non-degradable protein (DUP). ERDP, which constitutes by far the largest portion of fresh feed protein, can be broken down by rumen microbes and converted into microbial protein, which is later digested. DUP passes through the rumen intact and can be broken down and digested in the small intestine.

Protein range in grass

Crude protein content can vary within individual cultivars and between cultivars and is influenced by management factors such as nitrogen fertilizer application and crop maturity.

The proportion of crude protein available as real protein is lowest in the period after nitrogen fertilization, but increases as the grass grows and converts non-protein nitrogen into real protein.

In silage, the proportion of crude protein available as true protein is influenced by fermentation. Better fermentation ensures that more of the crude protein remains as real protein.

Get the most out of grass proteins

Animal research has shown that typically only about 20% of the protein consumed by ruminants is used to sustain the animal and produce meat or milk. The rest is lost in waste products and excreted from the body.

A better balance between protein and energy supply to the rumen will improve the protein portion used. Forages (such as grazed grass or silage) with higher sugar content (WSC) have been shown to improve protein utilization in ruminants.

Given the optimal balance between protein and energy sources, the concentration of crude protein in the diet can routinely be as low as 12-14% DM without any detriment to livestock productivity (14% for milk production).

Grass protein guide

• Apply fertilizer as soon as possible after grazing or mowing in accordance with best practice guidelines
• Avoid making silage that is too wet (less than 28% DM) as this can lead to loss of soluble protein in the effluent
• Optimal protein concentrations occur 3-5 days after mowing or grazing

The clover effect: Grass protein

white clovergenerally contains more protein than ryegrass. It is important to maintain an optimal balance in grazing fields of an average of 30% dry matter throughout the season.
Red clover is a high protein food (typically 22% crude protein). It contains an enzyme (PPO) that helps maintain the proportion of real protein in silage.

Grass fiber

Why grass fibers are important

Fiber is essential in the diet of ruminants and provides the 'scratch factor' essential for stimulating rumen function. There is an important balance that must be achieved in all diets for optimal performance.

Fiber is measured as NDF (neutral detergent fiber), the insoluble fiber fraction (cellulose, hemicellulose, pectin and lignin) remaining after cooking in a neutral detergent solution.

Carbohydrates in NDF are not as readily available as those in the WSC component of ryegrass. However, NDF content is important for predicting voluntary intake by ruminants.

The proportion of NDF that can be digested by ruminants is called dNDF. This is a secondary source of slow-release carbohydrates that provides a useful source of fermentable energy for ruminants in the rumen and large intestine.

The selection of fibers in grass

During the growing season, the grass fiber concentration can vary greatly. It is at its peak (and least digestible) when the grass produces reproductive seed heads instead of vegetative leaves. Conversely, fiber content is typically lowest in early spring when fresh growth is at its peak (grass is most digestible).

Get the most out of fiber in grass

The primary purpose of fiber is to maximize voluntary animal intake while ensuring adequate rumen digestion. For grazing, the optimal NDF content of grass should be between 30-40% of total dry matter, with dNDF being approximately 20-30% of total dry matter or approximately 60-75% of total fiber in a digestible form .

When grass fiber content falls below these optimal levels (e.g. early spring flushing), supplemental feeding of fiber may be necessary to prevent the grass from passing through the rumen too quickly.

When making silage it is important to mow before the grass is too mature (pre-silage) to avoid a significant reduction in digestibility.

Intake of grass fibers and dry matter

Directions for grass fibers

• Rotational grazing (18-25 days) using the Three Leaf System to determine when to graze optimizes both NDF and dNDF content in the grass
• Topping will remove stem growth and encourage new growth (and prevent NDF from becoming too high), but good grazing management should ideally avoid the need for topping
• Mow the silage in front of the grass heads to prevent NDF from building up too high
• Manage grazing and mowing of pastures to prevent diseases (e.g. crown rust, leaf spot) that will increase NDF at the expense of overall quality

The clover effect: fiber

The fiber concentration of white and red clover is lower than that of ryegrass and may potentially increase voluntary intake.

The physical form of fibers in clover generally breaks down more quickly in the rumen than the fibers in ryegrass.

lipids (oil)

Why are lipids important in grass?

Lipids in forage grass contain a high level of polyunsaturated fatty acids (PUFA). It is the 'good' fatty acids, better known as Omega 3 and Omega 9, that have positive health effects for humans.

From an animal production perspective, it has been shown that a greater supply of PUFA improves animal fertility and has positive effects on meat quality (longer shelf life and better color). There is also evidence of reduced methane emissions from ruminants eating feed high in PUFA, an effect that is positive for the environment.

Get the most out of the lipids in grass

Lipids have approximately twice the energy content of carbohydrates (WSC and fiber) and are an important source of energy for livestock. Ruminant diets are often supplemented with high lipid feeds as a means of increasing the energy content of the diet.

The selection of lipids in grass

Early data suggest that the total fatty acid content of grass ranges from approximately 2.5 to 5% of forage dry matter, with the PUFA component accounting for 65-78% of the total fat content.

Current and future grass breeding programs at Germinal Horizon have identified lipid concentration and fatty acid profile as important targets.

Lipid guide

• Fresh grass offers a better PUFA profile than many dry foods
• Forage-based systems have the potential to produce better quality human food due to the favorable PUFA profile in grass
• In silage production, rapid wilting will increase the level of retained lipids in the forage

The clover effect: lipids

The lipid content of white clover is generally slightly lower than that of ryegrass, with a range of 2-4.4% dry matter.

red cloverIt is generally reported to contain more polyunsaturated fat than ryegrass.

Minerals and vitamins in grass

Why are minerals and vitamins important in grass?

Minerals include various elements such as calcium, selenium and iron. These basic elements, like the more complex vitamins, play an important role in the health and performance of livestock. Understanding the mineral and vitamin content of grass is important for any additional supplementation that may or may not be necessary.

Get the most out of the minerals and vitamins in grass

Accurately managing a pasture for mineral and vitamin content requires a soil analysis for each pasture. If a mineral appears to be deficient, providing additional treats or mineral boluses can correct most deficiencies.

The range of minerals and vitamins in grass

The mineral content of a grass species will largely depend on the mineral availability in the soil and the pH. The mineral and vitamin content will not normally change in silage, although some losses to the effluent may occur in very wet crops.

Although many vitamins are synthesized by rumen microbes, some fat-soluble vitamins must be obtained from feed (vitamins A, D, and E), and all vitamins from feed can be a useful addition to the diet of ruminants.

When livestock is converted to lush pastures with fast growing grasses, especially in spring, it is advisable to monitor them to further reduce the risk of tetany. Supplement rations with minerals according to silage analysis.

Overview of availability of grass nutrients

If you have any questions about the nutritional value of grass,Contact one of our agricultural grass seed experts.

Originally published onGerminal.co.uk as 'the nutritional value of grass'.