The methods of grazing a brassica forage crop will vary between crop types, stock classes and the resources available to the producer. Some general suggestions are presented in the following sections.
Strip grazing these crops will achieve three key outcomes:
Strip grazing will improve utilisation, and combined with back-fencing, will allow maximum regrowth potential for rape and leafy turnips. Realistically, particularly for summer lamb fattening on brassica crops, set stocking remains the more practical option for brassica feeding.
Sudden unrestricted access to a brassica forage crop can upset the balance of rumen microbes, resulting in poor animal performance, scouring and rumen acidosis, particularly in cattle.
Start a feeding programme by grazing the crop for no more than 1-2 hours per day, building up to a maximum allowance over at least 7-10 days. Allow rumen microbes time to adjust to the high-quality forage.
Adapt the animals to the new feed gradually. Most animals going onto a brassica crop have come off pasture. Pasture is usually of lower quality than brassicas, and the rumen contains different types of microbes than those needed to digest brassicas. If animals suddenly access brassicas, there can be a sudden overgrowth of the wrong types of microbes, which produce large quantities of acid (rumen acidosis). Reduce risk of rumen acidosis by offering animals other non-brassica feed (pasture, silage and/or hay) before moving animals onto crop.
Pasture or supplements as part of the diet help maintain a normal rumen function. Feeding supplements before a new break of brassica reduces the risk of dominant, hungry animals gorging/overconsuming brassica.
Forage crops are highly digestible, and don’t contain much ‘effective fibre’, the sort of fibre that encourages animals to chew. Feeding extra effective fibre means:
Animal performance on brassicas is best when crops are fed strategically as part of a balanced diet. For example, the high protein and energy of brassicas complement stalky summer ryegrasses which can be deficient in energy content and protein, or whole-crop cereal and maize silages which are low in protein. Feed dry stock no more than 70-80% of the diet as brassica, once transitioned onto crop. Feed lactating dairy cows no more than 33% of their diet as brassica if milk is being sent to the factory.
Although the water content of brassicas is high, it is recommended that animals always have access to clean fresh water, as a limited water intake may cause an animal’s dry matter intake to decline.
Feeding brassicas can sometimes be associated with animal health problems. Risk can often be avoided by good agronomic and grazing management.