Brassica Feeding over the Dry Period – The Good, the Bad and the Ugly

/

Next to fodder beet, brassicas (rape, kale, turnips and swedes), are the other mainstay of the winter diet. It helps to understand some of their properties to get the best from them.

The Good

  • In kale, the upper 2/3rd of the plant has quite good ME – being about 12.5MJ. The lower part of the plant (the stalk) will be lower and is only about 7ME close to the ground. The overall ME is about 11-11.5MJ/kgDM. The ME of all other brassicas are closer to 12MJME.

  • Generally speaking, brassicas have good levels of crude protein for a dry cow – 14- 18%. This makes it quite a good crop to finish the winter on if you have had cows on a low crude protein fodder beet through the early part of the dry period.

  • Kale/Rape have high levels of calcium – about 3 times what is in grass and 9 times what is in fodder beet bulbs. This makes it handy for replenishing bone stores in dairy cows.

  • A tall grazing face can form good shelter for cows if being grazed in a southern direction.

The Bad

  • Kale crops often have bad utilisation in bad weather – it can be as low as 50%. Make sure you allow for this.

  • Best practice is to work on 80% utilisation in good conditions. If it is higher than this, cows are probably being underfed. Make sure you factor this in on your daily allocation.

  • All brassicas are low in effective fibre (and yes that includes those chewy looking stalks). This is the reason that as a minimum 25% of the diet needs to have a long fibre source – e.g. straw, hay or baleage.

  • Animals often ingest quite a bit of mud while on crop – this will deplete copper stores. Selenium is also consumed/depleted soaking up ‘free radicals’ created by a high content of poly-unsaturated fatty acids.

  • Swedes can be quite hard, making it tough for calves and heifers to eat. It can tend to be lower in crude protein as well.

The Ugly

  • The lack of effective fibre and if fed frozen can make cattle prone to frost bloat (a free gas bloat). The cold temperature shocks the rumen disabling the ability to belch. Wait for the frost to come off before feeding.

  • Brassicas will bind up Iodine which can result in still births in calves – particularly out of heifers. Dosing a trough with stock iodine on a daily basis in the last month of gestation may reduce this risk.

  • Nitrate poisoning is a real danger - particularly in rape followed next by kale. Its most likely to occur after periods of cold, low light conditions, where leaf loss has occurred from previous breakouts, and when animals go onto a frozen crop with an empty belly.

  • Like fodder beet, swedes can cause acidosis. A transition period is also important.