Equation change will give more accurate silage data

Farmers having silage analysed in the next few weeks may spot some differences in the metabolisable energy (ME) values recorded, after changes to the equation used to determine silage energy values.

Thanks to these changes, silage analysis undertaken this year by Forage Analytical Assurance (FAA) Group members should be more accurate than in previous years.

And while farmers will see some differences in analysis of crops with high digestibilities, this will have little effect on rations made with them, says John Allen of FAA.

“The new equation reduces the energy of high ME silages, so the need to manually correct rations by farmers and nutritionists has disappeared.”

Farmers normally making silages with metabolisable energy values above 10.2MJ/kg of dry matter will have lower energy predictions than previously, although the effect only becomes significant after an ME of about 10.8, he says.

“Silages which previously had low energy predictions – below 9.6ME – will now have higher energy levels, but average silages shouldn’t be affected.”

The new equation was developed to account for the rise in the amount of high dry matter silage being made in recent years, adds Dr Allen.

“Most users won’t see much difference, but the ME of higher quality silages will be lower.

This reflects the generally held view that grass silages with ME values of more than 11 often fail to perform as expected, which has led to many nutritionists making ad hoc corrections.”

And with first-cut silages already being analysed, this year’s crops look like feeding better than many had predicted.

While consultant Pete Kelly only has about 40 grass silage samples analysed so far this year, he is confident results are better than producers will have been expecting.

“With limited grass available at cutting time, I was predicting ME values in the region of 10-10.3, but already samples have analysed at 11Me and above.

“And with fibre results up on last year, analysis so far indicates a positive outlook for butterfats this year.”

Producers will, therefore, have to consider feeding less supplemented fat than last year to carry cows through winter, he advises.

But the later cutting dates imposed by this spring’s slow growth have meant silages analysed are a little lower in protein than many may desire, says Keenan Rumans nutritionist Hefin Richards.

“However, while some farms will be worried by the late cutting, it hasn’t been as detrimental as it could have been.

The late, cold spring meant grass wasn’t as far forward as normal, so despite some cutting dates being up to three weeks behind normal, they were actually probably only a week or so behind the optimum.”

Lower protein levels should not create too many problems, as this will be relatively easy to balance, he says.

“Although these crops are unlikely to push yields too much, the drier bulk will help maintain rumen health.”