Effects of harvesting immature maize crop

Published 5 September 12

The erratic weather conditions seen in many parts of the country over the maize growing season will have a number of implications in terms of variation in yield, maturity and nutritional value of this winter's maize silage.

DairyCo extension officer Tom Goatman talks about what effect harvesting an immature maize crop has and how to manage the associated problems.

The optimum time to harvest maize is when the maximum starch yield has been reached, balanced with optimum dry matter (DM) to aid consolidation in the clamp. The aim should be to try and achieve a DM of 30-35% but this is likely to be difficult to attain in many situations this year.

Because of the poor start many crops experienced, and the subsequent high rainfall and lack of sun, much of the 2012 maize harvest will struggle to reach maturity and optimum DM before the end of the season.  Couple this with increased pressure on forage stocks in many cases, due to farmers having to feed ensiled forages during the grazing period, and it is likely that a large proportion of crops may be harvested at an immature stage. 

There are some important considerations to be aware of both in terms of ensiling and utilisation of immature maize in diets this winter.

Immature silage will have a lower DM (around 25%) with an increased risk of effluent run off leading to loss of nutrients. Wetter silage will also reduce total DM intake.

Immature maize will generally be higher in digestible fibre, slightly higher protein and slightly lower energy than maize harvested at optimum maturity. This maize will have a lower starch content but higher concentration of fermentable plant sugars compared to a more mature crop. It will mean the crop should ensile well, as there is a high proportion of plant sugars available for fermentation, which will lead to fast drop in pH, inhibiting undesirable bacteria growth.  

The lower DM will help clamp consolidation and this coupled with the lower starch content should reduce the risk of aerobic spoilage during feed out.

But the lower DM in partnership with a high proportion of fermentable plant sugars could lead to an extensive fermentation and produce a more acidic silage. Higher levels of residual sugars will also be rapidly available to microbes in the rumen and this coupled with low silage pH and low effective fibre may increase acidosis risk.

The kernels of immature maize will require minimal processing but it is important to monitor what is coming out of the harvester into the clamp in order to check that particle size is correct and that more than 90% of grains are broken.

Think about increasing the length of chop of immature maize to around 5cm, this will help to increase effective fibre in the rumen. This in turn will help in stimulating rumination and saliva flow, and buffering of rumen pH reducing acidosis risk.  

If weather conditions are cool and poor in the weeks leading up to harvest there could potentially be insufficient naturally occurring lacto bacilli bacteria present on the crop to produce a desirable lactic fermentation.  This could lead to a reduction in the ratio of lactic acid to acetic acid during fermentation which is undesirable, so give some consideration to treating with an effective additive.  An additive should also be considered if there is a risk of soil contamination, for example when harvesting in wet conditions.

Ensure good clamp management during harvesting and make sure the clamp is well sealed.  Think about using an oxygen barriersheet to ensure an air tight seal.  Attention to detail to all aspects of harvesting will ensure clamp losses are kept to an absolute minimum.

Once harvested early analysis will be important to assess the initial nutritional quality of the crop and help with winter ration planning. But regular sampling over the winter period will still be necessary in order to monitor nutritional quality changes and avoid ration imbalances.