The impact of overgrazing on forage production

Overgrazing can significantly slow grass growth. It occurs when plants are grazed before they've had enough time to rebuild their energy reserves and recover their root system. 

Getting the timing and severity of grazing right helps maintain productive plants, protect soil health and support faster regrowth when conditions improve.

Grass plants rely on their leaves to capture sunlight and produce energy through photosynthesis.

Younger leaves are more photosynthetically efficient but grazing too frequently or too tightly can remove the plant's ability to produce enough energy to support rapid regrowth. 

Grazing below the two-leaf stage can reduce grass growth by up to 85%. 

In summer, regrowth of the first new leaf can begin around three days after grazing. As the plant develops, each successive leaf contributes more to overall sward production: 

• Leaf 1: contributes around 10–15% of grass production 

• Leaf 2: contributes around 30–40% 

• Leaf 3: contributes around 45–55% 

This is why allowing the plant to reach its full photosynthetic potential before grazing is important. 

A useful target is to graze at around 8–10 cm, leaving a post-grazing residual of 4–5 cm. 

The remaining stubble contains sugars and energy reserves that help the plant produce its next leaf after grazing. 

During grazing, plants also reduce root growth. Under continuous or very frequent grazing, roots therefore tend to become shallower because plants do not have sufficient time to rebuild their root reserves. 

Giving grass an adequate rest period between grazing allows these reserves to be replenished and supports stronger root development.

Good grazing management is about protecting root reserves while keeping plants in a productive, vegetative state. 

In general, shorter grazing periods and longer rest periods provide more opportunity for roots and plants to recover. 

Overgrazing reduces root reserves, which can prolong the time needed for grass to recover and produce new leaves. 

Healthy plant cover and a well-developed root system also help the soil take in and retain moisture.

Overgrazing can reduce plant cover and contribute to a decline in soil organic matter, including humus and glomalin, reducing the soil's capacity to absorb and retain water.

Rainfall may provide some needed moisture, but it doesn't mean grass is immediately ready to carry normal grazing pressure. 

You may need to continue to feed supplementary forage or other feeds to help meet livestock demand while protecting grass cover. 

Maintaining higher post-grazing residuals can also help by shading the soil surface, reducing soil temperatures and limiting further moisture loss. 

Even after rainfall, avoid putting too much grazing pressure on recovering swards. 

Grass may need around 21 days to rebuild root reserves and produce enough new leaf area before being grazed again. 

Where necessary, consider: 

• Continuing supplementary feeding 

• Reducing grazing pressure 

• Using sacrifice fields or areas that may need reseeding 

• Allowing damaged paddocks to recover later in the year 

• Prioritising the best-performing fields for grazing 

The aim is to protect the productive capacity of the sward rather than simply maximise grazing days in the short term.

Dry conditions can limit grass growth and reduce the plant's ability to take up nitrogen (N).

Applying additional N when there is insufficient moisture for active growth is unlikely to give a good response and increases the risk of N losses to the environment. 

Following rainfall, previously mineralised N in the soil, or N that was applied but not utilised during dry conditions, may help drive initial recovery growth. 

Additional N may then be needed to boost grass production, particularly where silage cuts are still required. 

Only apply N when soil moisture and growing conditions are sufficient to support active grass growth. 

As conditions improve, N response is likely to be lower than in spring.

On high-fertility soils, a response of around 10–15 kg dry matter (DM) per kg N may be achievable, although this will vary depending on soil fertility, moisture, temperature and growing conditions.

Rainfall following a prolonged dry period can also increase the risk of parasite challenges. 

Dry conditions may have reduced the number of infective larvae available for livestock to ingest, but larvae can survive in the soil and may become more active as moisture returns. 

Regular monitoring is therefore important.

Where appropriate, use faecal egg counts (FECs) and monitor livestock performance and liveweight gains to identify whether parasites are affecting animal performance. 

Avoid treating livestock routinely without evidence of a need to do so. Targeted monitoring can help ensure treatments are used effectively.