Maize residue, the straw left over after grain harvest, is proving a popular form of feed for dry dairy cows. Despite the drought breaking rain in the Waikato last month, dry conditions still prevail and many farmers are struggling to build pasture cover for winter.
DairyNZ recommends maize residue as a feed option only where there is insufficient pasture cover on a dairy farm (less than 1700 kg DM/ha) and pasture silage or hay is not available. If the feed situation is better than this, other options will provide better use of time and money.
Around 20,000 ha of maize grain is grown around the Waikato, Northland, Bay of Plenty, Hawke’s Bay and Gisborne regions, and the resulting crop residue is made up of stem, leaf, husk (the wrapper leaves around the cob) and rachis (the core of the cob). The residue, which can yield up to 13 T DM/ha is normally incorporated back into the soil, but this season is being baled to supply stock feed for drought stricken farmers.
While maize residue may be plentiful and very filling, the feed value is low. Tests conducted by the Foundation for Arable Research (FAR), the industry levy organisation responsible for maize research, indicate that baled maize residue, excluding the rachis or cob centre, has an energy value around 7 MJ ME/kg DM. That means an intake of 9 kg DM/ha/day is needed to feed to a 500 kg dry dairy cow at maintenance levels.
Tests also show that maize residue is high in fibre, with an NDF content of 70%, (typical range for other forages, 35-50%). This high level lowers digestibility. “Farmers should be aware that the high fibre content of maize residue will limit dry matter intake” says Chris Glassey, a farm systems scientist with DairyNZ.
“Maize residue should be viewed only as a source of long chop fibre for dry cows” says Mr Glassey, “and due to gutfill effects, cows in late gestation will struggle to maintain cow condition if fed solely on maize residue”. For this reason it’s really only an option for feeding the later calving cows in the herd.
Mr Glassey recommends that maize residue is fed with supplements such as molasses and feeds with a higher protein content such as grass silage or palm kernel extract to improve both the palatability and value of the feed. “Don’t give cows ad-lib access to molasses to avoid cows gorging themselves and suffering complications such as acidosis. Make sure cows develop a taste for the maize residue with low
levels of molasses added at first”.
Mr Glassey also recommends that magnesium supplementation is considered if cows are fed on maize residue for more than 3 day continuously. Maize residue only contains 0.1% magnesium, around half that of typical pasture. Where it is not possible to supplement magnesium directly though the water supply or by dusting, magnesium bullets should be considered.
“Farmers should also be aware that when they're buying in maize residue they will also be importing nutrients onto their farms” says Andrea Pearson, Research Coordinator at FAR. “Maize residue, at an average dry matter content of around 55%, will be bringing in around 4 kg N and 6 kg K per fresh tonne. Dairy farmers should take account of these imported nutrients when preparing nutrient budgets for next
season.”
The Foundation for Arable Research (FAR) and Environment Waikato are issuing a warning to all purchasers of baled sweetcorn and maize crop residue to be on the lookout for two invasive weeds, broomcorn millet and alligator weed.
Crops residues from Gisborne and Hawke's Bay may contain the invasive and difficult to control grass weed, Broomcorn millet (Panicum miliaceum). This grass weed, which is becoming increasingly prevalent in these regions, has a hard black persistent seed which could establish itself in other regions next spring if brought in the with baled crop residues.
Alligator weed (Alternanthera philoxeroides), which is prevalent in Northland, is an extremely invasive weed which outcompetes pasture and crops, and is toxic to livestock. It grows very easily from even the smallest of fragments.
Farmers buying in crop residues from these regions should note where on the farm it is being fed, and to be vigilant next spring and summer for the presence of these invasive weeds. AgResearch and FAR are currently investigating control measures for broomcorn millet and early results should be available for the coming season.