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Forage crops

Are the forage crops in place now coming to the end of their lives or are they being carried into the winter? If to be replaced before the winter it is a matter of consuming as much of them as possible.

Late summer is a time when deaths can occur, for two reasons. Firstly, by now the stock are well adjusted to the crop and can have very high intakes, especially if trying to consume as much before the crop is replaced. Their susceptibility to Clostridial infection is high and any weakness in the Clostridial vaccination background will show up then. The other common cause of death is when the crop is spelled to let it recover before the next graze. With late summer rain that recovery can be rapid and nitrate levels can accumulate. The returning grazing stock are well adjusted to eating it and can immediately consume a lot. Even mildly elevated nitrate levels can be lethal because the intake is fast and high. Always beware of regrowth crops.

This also applies to crops that have a summer graze but are then taken into the winter. That risk is particularly high if the same animals that had the summer graze also get it in the winter. They will adjust quickly and consume a lot. But even new entrants can succumb if the nitrate levels have got very high by the time of the first winter graze.

The risk of Clostridial deaths is always higher for stock grazing crops. This is due to a combination of factors but in particular the high “sugar” level in the crop and the high soil intake. Vaccinating before crop grazing should be standard practice. For most farms the basic 5-in-1 vaccine is sufficient. Full protection is not achieved until after a booster vaccination four to six weeks after the sensitiser. On some farms other Clostridial species are present, requiring 6-in1-or 10-in-1 vaccine.

Any other negative impact of a summer crop will by now be apparent. The most common of these are photosensitivity, commonly called rape scald. This can occur for no obvious reason, but often grazing an immature brassica crop or using high levels of sulphur fertiliser can be behind the problem. Lower live weight gains than expected will now be apparent. This is more common with summer brassica crops. Being introduced too early can result in a low weight gain for the first two to three weeks. Access to other supplements can reduce live weight gains. If the supplement is of lower feed value than the crop it will substitute for crop intake and so reduce the intake. This happens very often when silage is used as a feed supplement for cattle on crops. For brassica crops though, high weight gains are hard to achieve because there is a limit to intake, no matter what is offered. This creates a ceiling to the weight gain.

For crops grown only for winter use, the risks discussed above all apply. Winters are warmer so crop growth is very often good. This means that nitrate poisoning is a risk that we see frequently now. As for any crop, gradual introduction and even allocation protects against most of what can go wrong. Animal health problems that can occur on winter Brassica crops are redwater or haemoglobinuria. This is when a toxin accumulates in the leaves and if eaten in enough quantities causes the red blood cells to disintegrate. The consequences are much higher in pregnant animals. Regrowth is the most dangerous. These animals are very dull and hard to move. Treatment options are limited so early identification and removal from the crop is important. A swelling of the brain syndrome is another problem occasionally seen. It is usually individuals and they are blind and very dull. These are very successfully treatable if caught early.

Fodder beet grazing has a very high Clostridial risk. But most losses on this crop are from over-eating. Frequent and even allocation is important.

In summary:

  • Ensure full Clostridial vaccination before crop grazing
  • Introduce gradually
  • Allocate frequently and evenly
  • Beware of regrowth and re-introduction
  • Watch closely