Most animal health problems in brassicas are seen in the first few days of feeding them, particularly if hungry animals are put onto a crop. Stock intake of brassicas can be very high, and in some cases this has led to rapid death of animals.
Problems are much less likely to occur when animals have adjusted to a crop, and have access to another source of feed or pasture to eat in conjunction with the brassica crop. A small percentage of animals do not perform well on brassicas, so stock should be monitored, and poor performing animals removed from the crop.
Out-wintered cattle have a higher energy requirement compared with those housed indoors and at least 15% more feed energy may be required.
Only allow “full” cows onto the crop initially and only for short periods to begin with.
Forage brassicas are concentrated sources of energy (ME) and crude protein and should be considered as concentrate feeds, hence the need to introduce them slowly into the diet. As high quality feed sources they can be classified as 'wet concentrates' rather than as 'wet forages'.
Brassicas are lacking in structural fibre and rations containing significant proportions of the dry matter as brassica should contain coarse fibre, such as straw, to maintain rumen function
On-farm experience in New Zealand suggests that no more than 50-60% of the total diet DM should be brassica with the remainder of the diet made up of fibrous forages as required to meet the nutritional needs of the animal and avoid rumen acidosis problems.
Brassicas can be high in nitrate-N which can cause nitrite poisoning when nitrate is converted to nitrite in the rumen, particularly when young, leafy brassica crops are fed and the diets are also low in soluble carbohydrates
Always make minerals available (specially formulated if required).
The calcium and potassium contents of forage brassicas are high and limit their use in rations for dairy cows close to calving.
The manganese, zinc and cobalt content of brassicas is also either marginal or low.
The brassica crops are particularly deficient in copper, iodine and selenium and must be be supplemented.
Don’t feed “close-to” calving cows on brassica crops – manage them separately.
Experience in New Zealand shows that splitting the “dry” period into the “far-off” and “close-to” calving periods is also considered essential to ensure correct nutrition, particularly with respect to mineral feeding.
Cows should be changed from brassica-based diets three weeks before calving and cows and in-calf heifers close to calving should be moved inside to a drier, cleaner and warm environment to minimize the risk of disease and also calf mortality. The risks associated with calving problems when the cows are less accessible - maybe calving when conditions are wet, cold, muddy, snowy or dark - are too great when cows are kept out.
Diets need to be changed gradually when cows change from a pre-calving high brassica/low concentrate diet to a post-calving diet based on both a different forage and a high proportion of concentrates.
The combination of moving cows from outdoors to an indoors environment and changing groups should be avoided.
Brassicas can contain high levels of calcium and only marginal levels of phosphorus. They also contain low levels of magnesium but high levels of potassium. This imbalance in minerals is conducive to milk fever. It is best to avoid feeding brassicas to springing cows - springers should be transitioned to a grass based diet at least two weeks before calving
DM - 10-17%
ME – 11-13 MJ/Kg DM
CP – 12-20%
DM – 12-14%
ME – 10-11%
CP – 18 – 20%
DM – 12-14%
ME – 10-11%
CP – 18 – 20%
DM – 8-10%
ME – 10-11%
CP – 18 – 20%
Roches Feeds
Dock Road
Limerick
