29 January 1999

Is total energy a better measure?

Should we change the way in which we test maize varieties?

French breeders certainly think so. Simon Wragg reports

FRENCH maize breeders want to change the way UK producers pick varieties. While NIAB figures for cob ripeness – as an indication of starch content, but often at the expense of overall yield – will influence many decisions, the French argue that total energy yield and overall digestibility are more important.

The argument put forward by breeder Limagrain is that while a maize cob contains more plant starch, it only contains half of the total energy available.

According to the companys nutrition specialist Michèle Champion, green plant material also contains energy. This is in the form of soluble sugars which digest in the rumen within a few hours. Overall, almost 50% of all plant fibre is digestible, enforcing the argument that cob ripeness is just one criteria for selecting a maize variety.

Limagrains UK spokesman, Peter Schofield, adds that total plant energy yield is under-valued: "From a nutritional point of view, its essential to produce sufficient maize to feed through a 200-day winter. Where producers run out of maize because theyve picked a variety suited to their site, but with a low energy yield/ha, the effect on performance from a change in diet can be profound."

Response from the domestic market to this argument has been muted. UK nutritionists say its flawed; maize is only a small proportion of most forage rations and its quantity of starch, not energy, that matters most. They suggest ensuring that grass silage is high in energy is more important as it forms the largest part of the ration and suffers the greatest variation in energy content.

However, Limagrain argues that cob data can be misleading in other ways. For example, theres little correlation between cob ripeness or hardness which is used as an indication of yield compared with whole plant dry matter. Theres also the question of plant digestibility which peaks at 27% DM while starch content continues to increase as the plant matures.

Research at Limagrains animal nutrition unit is looking at whether the breakdown of maize silage with different starch contents can significantly affect feed intake. A high starch maize can reduce rumen pH and restrict feed intake to a greater extent than maize silage with a lower starch content, explains Ms Champion.

Most maize in the UK is cut at 30% DM or more to maximise starch, but often at the expense of overall digestibility. To correct this, Limagrain says digestibility data should replace cob ripeness in influencing variety choice.

Currently, UK producers use digestibility figures calculated on freshweight samples in NIABs Descriptive List for maize. On this point Mr Schofield says the NIAB list doesnt go far enough. While freshweight digestibility relates to a plants overall digestibility, it can vary greatly from that of maize silage due to chemical reactions during the ensiling period.

NIABs Jim McVittie, and the MGA agree theres merit in the argument for including ensiled maize silage analysis in national testing. But with more than 150 varieties in the testing programme the cost could be high.

"Breeders would have to pay for the extra testing. With the UK market for maize seed relatively static, many may be reluctant to invest," says Dr McVittie.

A major player in the UK market, GrainSeeds John Hardy says reasons for not including ensiled maize analysis go beyond cost. It would add more variables to the testing system and might only complicate producers choice, he says.

But most parties should unite behind testing of a broader selection of maize varieties across the full range of growing areas, from ideal to marginal, says Mr Hardy. This is already being included in NIAB national list trials and should give a broader set of results from which varieties can be picked.

VARIETYCONTROVERSY

&#8226 French proposing changes.

&#8226 UK nutritionists disagree.

&#8226 NIAB testing could change.

&#8226 Breeders must agree to pay.