Managing forages after rain | Beef + Lamb New Zealand
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Adverse weather

Managing forages after rain

While recent rain was welcomed in many parts of the country, it does bring with it management issues that need to be considered to prevent short and long-term animal health issues.
Tuesday, 15 February 2022

Post-rain management

  • Lush Lucerne should be treated with caution – add roughage, salt and consider mowing in front of stock.
  • Do not mate ewes on lush lucerne in warm, humid conditions.
  • If it has been very dry, resist the temptation to graze green growth in the wake of rain.
  • Consider an autumn application of nitrogen.
  • Look out for Facial Eczema, internal parasites and flystrike.

Lucerne

Lucerne crops will have responded to the moisture by producing a flush of highly-palatable fresh growth, but it needs to be grazed with care and should not be used for ewes over mating.

Professor Derrick Moot says lush lucerne should be treated with caution.

“Think about roughage, salt and potentially mowing in front of stock if the crop received more than 30mms of rain.”

If it was dry before the rain, there is an increased risk of high nitrate levels, so Professor Moot recommends starting grazing in full sunshine, when the nitrate has been converted to protein in the plants.

“Avoid grazing on dull, overcast days immediately after rainfall, especially with lambs.”

While it may be tempting to graze ewes on lucerne over mating, Professor Moot says hot humid conditions will increase coumesterol levels in the lucerne which can reduce ovulation rates by up to 25 per cent.

To reduce the risk, ewes should be taken off the lucerne two weeks before the ram goes out. They can be safely put back on the lucerne immediately after mating.

For up-to-date tips from Derrick, and the ability to ask questions of him, sign up for B+LNZ’s free lucerne text message service here.

Pasture

Farm Systems scientist Tom Fraser says it is important farmers resist the temptation to graze any green growth in the wake the recent rain to allow pasture plants to build root reserves that may have been depleted in dry conditions.

He says green growth after rain means the plant is photosynthesizing allowing root reserves depleted during dry spells to be built up again. This is especially important going into autumn and winter as those reserves will be essential to drive pasture growth in spring.

Grazing pastures too soon after rain could deplete root reserves even further and lead to the death of the plant.
Tom says spring forage supply is most critical and while farmers in many parts of the country are struggling with limited feed resources due to processing delays and dry weather, the way pastures are managed now will determine spring growth.

He says by mid-April it is possible to determine what spring growth will be.

“The more leaves those plants have the better spring growth will be.”

He says after rain, farmers need to stay in drought-mode for two to three weeks.

“The worst thing you can do for both plant and animals is graze green-tinged pastures, just stay off it.”

Short pastures can pose internal parasite and Facial Eczema risks to livestock.

Tom recommends farmers rank their pastures on a one to four scale (one being terrible and four not too bad) and treat the better pastures with kid-gloves over winter. They should be the last to be grazed in autumn and a dressing of nitrogen (N) could be considered.

“N applied from the end March through April, (provided soil temperatures remain above 7-8 degrees celsius in the top 10cm of soil and the pasture is actively growing) will help push feed forward into winter even though the response to the N may be small.”

He says farmers need to leave at least three weeks, but preferably longer, between application and grazing to maximise the response.

N applied in autumn helps grass plants produce new tillers which will grow in spring. Some of the N taken up by the plant may be stored in roots and can help the plant kick off in the spring.

Subterranean clover

Professor Derrick Moot says he has had many reports of subterranean (sub) clover striking now in the wake of recent rain, but adds that it is too early for the plants to survive into autumn unless more rain falls.

“To increase the chances of the current sub clover strike making it to autumn, stay off it until at least 3-4 true trifoliate leaves have developed on the plant and when you pull it the leaves/stems will break off rather than the entire seedling being pulled out of the ground.”

A light grazing at that stage will control the grass that will also have recovered, so young sub clover seedlings are not shaded out by the competing grass.

Professor Moot says one more 20 mm rainfall event will be needed in the next six weeks to ensure successful establishment from this strike. If this were to happen it would be an excellent autumn for sub clover. This would be a contrast the last couple years when late autumn breaks reduced sub clover’s ability to establish before it got cold.

Assuming successful establishment, sub clover may provide feed for ewes over mating so farmers don’t have to risk mating on lucerne.

Too much a good thing

While rain was welcome, the sheer volume of it caused some damage in isolated areas. B+LNZ has specific flood resources to support farmers as they enter the recovery phase.

In the first week, it is recommended flood-affected farmers make an action plan, prioritise tasks and revise their business plan, financial budget and feed budget.

Assess the damage to access ways fences, pastures (record type and depth of silt) and accept offers of assistance.

It is important to keep bank managers and insurance companies informed. Take photos of any damage and keep receipts for insurance purposes.
See our Flood recovery factsheet (PDF, 2MB) for further advice. 

Resources

Recovering from Drought

Lucerne management

Sub clover management