To get the best performance out of stock grazing brassicas and to avoid potential health problems there are some best practice guidelines or rules to follow:
Minimise exposure to toxic sulphur compounds. These damage red blood cells resulting in loss of appetite and varying degrees of anaemia and in severe cases redwater and death. Kale and Chou are worst for this. To help avoid this use low sulphur fertilisers e.g. DAP prior to sowing.
Allow stock to acclimatise to the crop. Initially run animals on crop 2 hours/day (about 20% of diet) building up to 100% of the diet by 7-10 days. Alternatively continue to provide a runoff block of older pasture. At the very least this will reduce the check that occurs when stock go onto brassicas and allow them to reach maximum growth rates sooner, but it could prevent deaths as well.
Feed extra fibre. Always feed supplementary fibre such as straw, hay, etc as this slows down the flow of feed through the rumen and gut and allows a more effective rumen fermentation and digestion. Studies have shown that lambs fed 0.2kg DM of straw/head/day had higher growth rates than those fed only brassicas.
Ensure stock’s trace element/vitamin status is OK. Studies have shown that applying mineral mixes containing selenium, cobalt, iodine and copper to soils that are low does not lift the levels in brassicas. Of main concern are iodine, Vit E and selenium levels in all stock and copper levels in cattle and deer. The first 3 can be corrected by administration of LSD - again a warning to beware of rubbish LSD copycat attempts. The exact timing of administration of LSD depends on a number of factors - length of time on brassicas, pregnancy status, Flexidine use etc - ask at the clinic for advice for your particular circumstances.
Break feed to allow better growth & utilisation. Studies have shown that cattle grazing turnips had significantly higher weight gains when shifted daily onto a fresh break than those given a new break weekly.
Removal from brassicas. Brassicas contain high levels of calcium and milk fever can result if stock close to lambing or calving are removed from brassicas and put on low calcium feeds such as early spring pasture. This is one of several reasons why I think it is preferable that ewes (and cows) are not grazed on brassicas with a month of the start of lambing (or calving).
Written by John Smart BVSc
Extract from May 2008 - Sheep Newsletter
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