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Considerations When Grazing Failed Crops

Monday, October 21, 2019

In many areas, this season has resulted in the consideration of what options are available to make the most of failed crops. Grazing is often common particularly in areas where the biomass is not sufficient enough to warrant baling for hay. It is important to evaluate the fragility of the soils in paddocks you are considering to graze. In some situations the benefits of some extra feed for your sheep may not outweigh the potential long term damage to soils that can occur as a result of inadequate ground cover compounded by the damage caused by sheep grazing a paddock.

With any failed crop, it is important to consider the withholding periods (WHP) on any chemicals applied, particularly fungicides, which tend to have lengthy WHPs. If a crop is still within a withholding period it must not be grazed by any livestock that are being sold for slaughter.

In many situations failed crops provide high quality feed as a result of good soluble carbohydrate levels. However high levels of soluble carbohydrates can put sheep in a high risk category for pulpy kidney. Ensuring pulpy kidney vaccinations are up to date is important and in some situations, if it has been three months since they were last given a vaccination providing an additional booster outside of the annual booster provides extra protection.

Failed cereal crops can provide excellent feed for sheep. Providing a supplement containing salt, magnesium and calcium is important particularly when grazing failed triticale and wheat paddocks.

Failed bean crops can be tricky to graze. Depending on the variety, tannin levels in the plants often make them unpalatable – particularly older varieties. Desiccating the crop can enhance palatability as can cutting the crop and leaving in windrows to graze. However unlikely it is in a drought, be mindful that if a rainfall event does occur, there is a risk moulds may develop which can produce harmful mycotoxins which impact on the palatability of feed and the health of sheep.

Grazing failed canola crops can provide good feed for sheep. Nitrogen applications will contribute to protein levels of the feed but can also result in nitrate poisoning in livestock particularly if the crop has been stressed. Nitrate levels should not exceed 0.5% for ruminants. Whilst health issues are uncommon, they do occur when grazing canola. Canola is generally high in sulphur and levels can be as high as 0.3-1.3% on a dry matter basis with the recommended upper limit for ruminants being 0.4%. High sulphur levels will result in polioencephalomalacia (PEM), whereby lesions develop on the brain and it often results in death. Canola in many instances should be fed at no more than 60% of the diet and therefore when grazing a failed crop other feed sources such as hay and/or grain should be offered.

Failed chickpea crops are unpalatable to livestock as a result of a malic acid coating on the leaves and are generally not a great option to graze. Sheep may consume some flowers, pods and new growth, but utilisation of the whole crop is poor.

Failed lupin crops often lack biomass and are often grown on lighter sandy soils which are more predisposed to erosion making them a high risk grazing option. Lupinosis, whilst uncommon on green plant material, can still pose a risk on a mature crop that has died, dried and experienced a rainfall event before grazing, however unlikely this might be in drought conditions.

When grazing failed crops it is important to consider the weeds present in a crop particularly in situations where herbicide application may have been reduced. Some weeds are toxic to livestock and under normal seasonal conditions, livestock would avoid these. In drought conditions, the lack of feed increases the pressure to graze weeds, potentially resulting in toxicity and death.

For further information contact your local Livestock Consultant.

Article written by Tiffany Bennett, PIRSA Rural Solutions SA