The choice of maize variety and harvest timings when making silage for dairy cows is largely influenced by site location.
However the total mixed ration (TMR) inclusion rate is another important factor for consideration, says John Burgess, of plant breeder KWS.
A 50 per cent maize silage inclusion rate for a TMR was considered high until fairly recently, but today’s average figure is about 65 per cent, says
He adds: “I would recommend sowing ultra-early or early varieties with an FAO, or maturity rating, of 170 and below for rations with a moderate maize silage inclusion rate.
“They have the potential for very high starch yields and their early harvest dates are helpful where an all year-round supply is required.
“Meanwhile, growers who use a high maize inclusion rate should sow a percentage of later-maturing hybrids, which offer superb yield potential and moderate starch. However, a starch content of 30 per cent plus should be set as a minimum for variety selection, in order to fully reap the nutritional benefits of the crop.”
The standard maximum for the level of rumen degradable starch in a TMR is 25 per cent, says Mr Burgess.
Figures of 25 per cent plus can lead to excess starch loading, thereby increasing the risk of acidosis.
“Maize is valued for its starch content and contribution to dietary energy,” he says.
“However problems can arise when high maize silage TMRs contain too much starch. This situation most commonly occurs when the crop becomes over-ripe as the result of a delayed harvest.
“In recent years, we have seen high autumn rainfall and maize harvests have not always been straightforward.
“As well as lifting starch content, a late harvest will reduce plant sugar and there will be a rise in the neutral detergent fibre percentage, as the material will be more alkaline.
“It is advisable to cut maize at the optimum 30-35 per cent dry matter, to ensure a stable fermentation and to promote intakes.
“It is worth noting that modern maize hybrids are coming into the clamp at higher dry matters compared with older types, and that the silage they produce tends to be less acidic.”
On some farms, the solution to minimising the risk of a late harvest is to plant ultra-early or early varieties, so that cutting can begin before the bad weather sets in, he explains.
“Tremendous genetic progress on maize breeding has been achieved over the past five years. Today’s growers have access to hybrids that take only 130 days from planting to reach maturity.
“Ultra-early and early hybrids generally have an FAO of 170 or below. They have been associated with a small yield penalty compared with mainstream types, but genetic advancement means many have caught up with their mainstream rivals.
“Their predictable performance, largely due to their early harvest dates, will allow the grower a greater degree of control over the crop’s feed-out properties.
“A short period from drilling to harvest can also be useful on dairy units with large acreages, where it can help to spread the workload at drilling and harvest times.
“Therefore, timeliness of operation can be enhanced by the inclusion of 20 per cent ultra-early and early varieties in the farm portfolio.”
Conversely, ME and starch content will be diluted if maize is harvested before it is fully mature, he says.
It will also be high in sugar and acid detergent fibre levels will be increased, due to greater acidity.
Modern maize hybrids supply an excellent source of energy, coupled with a yield stability that surpasses many other forage crops, he adds.
This consistency factor makes production costs relatively predictable, even in challenging weather.
Maize silages will remain stable for several years in correct storage and the crop can help with slurry utilisation.
Starch degradability will improve after the ensiling process, so at leasttwo samples should be taken over the winter to achieve the optimum inclusion rate.
In addition, a comparison should be made between old and new silages when switching from one pit to another.