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Grazing failed canola crops

By John Fowler, Senior Lands Services Officer – Mixed Farming Systems

August, 2018

Many of the winter crops in the Deniliquin district are showing the adverse effects of the current dry period.  Many of them, unfortunately, are not likely to survive until harvest (though thankfully there are some notable exceptions).  Crops that are not showing sufficient growth even for a spring hay cut are therefore likely to be grazed.

Canola crops appear to be the worst affected at this stage and is likely to be the first crop grazed.  Grazing is probably a good use of failing canola as it typically has a high feed value (i.e. high metabolisable energy, protein and digestibility).

However, landholders need to be aware of the potential dangers of grazing canola and the extra measures required to improve both the safety and performance of livestock grazing canola.  These include:-

  • care to avoid stock health problems from high nitrate levels (or other potential issues)
  • ensuring stock have access to a high-fibre supplement (grassy hay, cereal hay or straw)
  • adhering to grazing withholding periods for any chemicals used on the crop.
Livestock health
During previous droughts, there have been isolated incidences of illness and even stock deaths from grazing standing canola. Some of these problems were attributed to nitrate poisoning; others seemed to be due to respiratory issues caused by other toxic compounds.

When fed as more than 60 per cent of the diet, canola has also been known to cause digestive irritation, photosensitsation, anaemia, polioencephalomalacia (neurological problem) and blindness. Blindness issues have been reported to be more likely to be an issue if the crop was fertilised with sulphur.

Canola crops that have received high nitrogen inputs prior to becoming moisture stressed are likely to have dangerously high nitrate levels. This can be checked by conducting a feed test prior to grazing.  It is a good practice to initially introduce only a small number of stock and to monitor them closely, particularly for the first three days.  Avoid introducing hungry animals and provide access to some alternative or supplementary feed, either standing feed in an adjoining paddock or hay or straw in the same paddock.

Immediately remove stock if they exhibit any unusual behaviour.  Speak to a veterinarian for more information.

Access to supplementary feed
As indicated above, canola should not represent any more than about 60 per cent of the feed intake of livestock.  Additional high-fibre feed needs to be available to both improve stock performance and minimise toxicity issues.  The supplementary feed does not need to be high quality (i.e. good quality feed with high metabolisable energy, high protein and high digestibility) as the main requirement is for high fibre.

Supplementary feed can be in the form of baled hay or straw in the same paddock as the canola, or it can be standing feed (even poor-quality standing feed) in an adjoining paddock.  Be sure to move the stock into the paddock without canola within a few hours of the initial canola grazing.  This ensures the stock know how to access the adjoining paddock and lets them self-regulate their canola intake.

When feeding a green crop as a large part of the diet (although this is unlikely to occur in the current conditions), a supplementary lick of 1 part salt, 1 part causmag and 1 part limestone can help prevent issues with calcium and magnesium deficency.

Grazing withholding periods
All chemicals used on the crop, whether insecticides, fungicides or herbicides, will have grazing withholding periods indicated on their product labels.  It essential that these withholding periods be adhered to, even if the stock are not intended for sale.  For instance, Gaucho® 600 has a six-week grazing withholding period prescribed on its label.

This may be an issue for growers of triazine tolerant (‘TT’) canola.  Both simazine and atrazine have a 15-week withholding period.