Why starch is a critical quality criterion to consider when choosing a maize hybrid
This approach serves farmers well since starch accounts for a disproportionately large percentage of the energy yield and feeding value of maize silage, explains Andy Stainthorpe, UK & Ireland Business Manager for Pioneer Hi-Bred.
‘The total feeding value of maize silage is best characterised by its content of metabolisable energy (MJ ME/kg DM) since this is what is available to the animal through digestion. In typical maize silage most of the energy originates from starch, sugar and easily digested “plant cell contents”’ explains Andy. However it is important to also not forget that starch in maize silage is a very useful component of a ruminant’s overall ration simply because it degrades more slowly and therefore poses less of an acidosis risk than when cereal starch is included at an equivalent rate.
Whilst plant cell contents are close to 100% digestible the carbohydrates found in cell walls, usually referred to as the Neutral Detergent Fibre fraction or NDF fraction, (after the analytical technique that measures them) are far less degradable. Typically the NDF fraction is only between 50 and 60% digestible. Dutch data based on in vitro tests of commercialised maize hybrids showed an average NDF digestibility (or NDFd) of 47.8%. The simple conclusion from this is that about 66 – 75% of the digestible energy in maize silage is obtained from starch and sugar.
Despite a limited contribution to energy density, the NDF content of any forage maize is still an important parameter to consider in terms of ruminant nutrition. This is because the slower rate and extent of digestion of the NDF fraction increases the residence time in the rumen and it has been shown that excessively high levels of NDF can limit ruminant feed intake. It has been shown that actual dietary NDF quantity has 3 to 4 times the impact on intake and milk production as does NDFd ( i.e. the digestibility of that NDF). Hence it can be said that the first priority is to optimise NDF concentration and then fine-tune the result for differences in NDFd.
Accordingly explains Andy Stainthorpe selecting high starch hybrids such as Justina, Benicia and PR39V43 and using different methods of increasing starch content such as growing maize under film using The Samco System are critical to maximising the feed value of your silage.
The 2011 Pioneer Maize Trial Results Book or ‘The PACTS Book’ as it is known gives values for both the starch %, energy density (Mega Joules of Metabolisable Energy) and NDF % of all Pioneer hybrids grown either in the open or under film. This enables growers to compare the relative value of one hybrid against another and maximise the feed value of the silage they grow in 2011.
