Silage is perhaps the most common form of conserved forage on UK farms, but it may not be the cheapest incorrectly stored.

Per Lingvall, of the Swedish University of Agricultural Sciences, told Farmers Weekly at Scotgrass that using white or light green wrap resulted in better quality silage as it reflects 25-28% of light, resulting in significantly less heat in bales and so a more stable fermentation process.

Black plastic absorbs more heat and so fermentation can be less stable, resulting in a poorer quality silage overall, Dr Lingvall said. “Wrapping bales in the field also caused issues as fermentation starts soon after bales are wrapped and moving them after wrapping means more oxygen can enter bales as wrap is moved and gaps appear between layers.”

However, Rhys Fychan of IGER said in some areas of the UK light coloured film can prove problematic. “In National Parks there have been occasions where farmers have been asked to avoid using light green or white wrap as it is seen as a blot on the landscape.”

Additionally, Dr Fychan said wherever possible bales should be wrapped at stack sites to avoid damaging wrap and ensure fermentation was as good as possible. “Air entering bales once they are wrapped leads to mould formation and increased incidence of listeria. Where bales are wrapped in the field they should be moved to the stack site immediately after wrapping and should be handled and transported carefully.”

Production

On the production side, poor film seal results in silage which has a lower predicted intake and hence reduced liveweight gain or milk output, he explained.

Recent trials at IGER had shown that using six layers of wrap rather than four results in improved silage quality and, while it may cost 70p a bale more, generates benefits of more than £2 a bale.

“Another study concluded that mould cover on bales wrapped in six layers of film was just 0.75%, while in bales wrapped in four layers it was 1.75% – more than twice the amount. On top of this, predicted liveweight gain was 0.65kg a day from silage wrapped in six layers, compared with 0.62kg a day where bales had just four layers of wrap.”

For dairy farmers the figures are equally compelling, with cows eating silage wrapped in six layers predicted to give 13.87 litres a day from silage, whereas those fed silage wrapped in just four layers were predicted to give just 13.42 litres a day from forage – 0.45 litres less a day, he explained.

However, wrap layers are just one part of the story and the value of netting stacks to prevent bale damage by birds shouldn’t be underestimated. “Considerable differences were observed between the inner and outer bales within the stack.

“Outer bales had more mould and lower ME and predicted milk yield than protected inner bales. With more than half of bales being outer bales, even in a stack of 300, protecting a stack using a net is beneficial,” he concluded.