Care required with feed crops in autumn

At this time of the year, feed crops and pastures can be toxic to livestock particularly when frosts, overcast or cold weather follow a period of rapid growth. James White, from Seed Force, offers some advice.
Wednesday, 16 May 2018

Key points

  1. Nitrate poisoning is a risk in feed crops at this time of year.
  2. In high-risk periods, consider feeding the crop of pasture in the afternoon (particularly if sunny) when nitrate levels are lower. Check stock regularly.
  3. Feed stock before running them onto at-risk crops or feeds and ensure stock have access to supplement such as hay or silage.
  4. Allow an adjustment period for all feed crops- this is critical with cattle on fodder beet.
  5. Bloat can also be an issue if feeding frosted brassica crops.

Nitrate poisoning can occur when the plant uptakes more nitrogen from the soil than is able to be utilised.  James White, Commercial Extension Manager for Seed Force, says this can affect many species but most notably forage brassicas, short-term ryegrasses and oats.

He says grazing strategies such as not running hungry stock onto at-risk crops or pastures and reducing their intake by providing a supplement such as hay or silage (or a feed with low nitrate levels), will help minimise the risk.

Allow time for livestock to adjust to feed crops by gradually increasing the allocation over time. During high-risk periods, feed the pasture or crop in the afternoon as nitrate levels will typically be lower, particularly on sunny days says James.

Nitrate test kits are available, so farmers can test their own crops, or samples sent away from analysis. Levels exceeding two per cent of dry matter are considered unsafe.
All stock can be affected by nitrate poisoning, but cattle and younger stock are most susceptible.

James says nitrate poisoning can happen very quickly, so he urges farmers to check stock often during high-risk periods and animals showing any sign of illness should be removed immediately.
Acidosis is another risk factor when feeding forage brassicas, but this can also be minimised by introducing stock to the crop slowly, ensuring animals are not going onto the crop hungry and providing access to supplementary feed.

James says brassicas also contain anti-nutritional compounds (SMCO and Glucosinolates), but these can be managed through a slow transition and adequate supplementation.

Bloat can also be an issue if feeding frosted brassica crops.

Fodder beet

Careful transitioning is essential when feeding fodder beet crops, particularly to cattle.

The feed should be introduced to the animal slowly and the feed allocation gradually increased. This allows the animal’s rumen to adjust to a new type of feed.

It is important to know exactly how much feed you are giving animals over this transition period.

Crops should be measured and plants sent away for dry matter testing.

James cautions against using “book value” dry matter measurements as these can vary greatly with fodder beet and have a big impact on allocation due to fodder beet’s high yield potential.

During the transition period – which should last for at least 14 days – give the animals plenty of room with wide feeding- faces. Never run hungry animals onto the crop over this adjustment period.

Ensure the animals’ nutritional needs are being by providing the correct supplement with their crop diet. This will vary between different classes of stock.

Young cattle should be vaccinated with a 10-in-one vaccine before they are introduced to fodder beet.

Sheep are at less risk of acidosis on fodder beet so don’t need the careful transitioning used for other stock. While they can self-regulate their intake easier than cattle in the early stages of feeding, they should still be introduced to the crop gradually.