The generally lower quality of grass and maize silages produced during 2005 is jeopardising many herds' ability to maximise milk yields and fulfil quota, according to feed specialists Southern Valley Agriculture. SVA was formed after Mole Valley Farmers bought the southern business of Pye Bibby, including three feed mills at Calne in Wiltshire, Lifton in Devon and Dorchester in Dorset.

Dr Chris Bartram, the company's ruminant nutritionist, said: "The economics of producing extra milk are currently the best that they have been for some years. It is ironic that during what is an ideal time for most herds to push for higher production, unless urgent action is taken to improve nutritional performance many will fail to capitalise on this excellent opportunity to increase profitability."

SVA's analysis of hundreds of silage samples has highlighted an increase of almost 20% in the number of grass silages exhibiting low levels of energy, whilst those containing levels of crude protein below a critical minimum has increased by more than 50%. These variations have been accompanied by a 10% increase in silage samples with a high potential acid load, while those exhibiting typical levels of rumen degradable protein have declined by 35%. Maize silage shows an even greater fluctuation than grass. Forty per cent of maize silage samples analysed have been classified as low in energy. This is compounded by a reduction in samples containing high levels of starch.

"Higher acid loads in grass silage and lower levels of dietary fibre in maize silage combined with the fact that many herds are including more maize silage result in a challenging combination," said Dr Bartram.

"The additional acid makes it more difficult for bacteria in the rumen to function correctly, while lower levels of dietary fibre means that material passes through the system more quickly, reducing the rumen's ability to maximise output. Attention to detail is critical and must first include an evaluation of forage dry matter, daily intake and dietary fibre, together with an assessment of the impact of 'negative' ingredients such as wheat or biscuit meal.

"It is also important to monitor milk fat content, dung consistency, rumen stability and structural values. The second, concurrent, course of action is to ensure that ingredients needed to improve the rumen environment are available. This may include the use of sugar beet, soya hulls, chopped straw and high digestible fibre compounds and blends."