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DAIRY farmers should consider cutting their silage shorter to optimise rumen health and boost milk yields, according to new research.

There has been a tendency to advise long chop lengths to improve rumen health but this can be counterproductive, said Adam Clay, extension officer and feeding specialist for DairyCo (which replaced the Milk Development Council).

"Advisors often recommend adding longer chopped material to the diet to cure acidosis because it slows down rumen flow and allows the rumen to break down the material at a steady pace," he says. "This is correct, but often the cows will simply sort through the feed and end up overindulging on finer, starchy feeds and leaving the longer material aside, which actually encourages acidosis."

Acidosis - or low rumen pH - causes poor rumen function, reduced dry matter intake, poor feed efficiency and therefore reduced milk yield. "I tested a typical silage mix at point of feeding at 17% protein, which was ideal," says Mr Clay. "Four hours later it was just 13% protein, because the cows had sorted out the fine protein particles to eat. This would have been hugely detrimental to rumen pH and also left a lower than required protein diet available for the other 20 hours of the day."

To avoid this type of sorting, and improve overall silage quality, farmers should aim for a grass chop length of between 20mm and 25mm, he says. This results in a more unified mix in a total mixed ration, reducing the potential for selective eating by the cows.

"Because the chop length is shorter, rumen flow is quicker, which can increase dry matter intake and therefore milk yield. However, you must take great care with diet composition, particularly in the use of forages and straights, so as not to actually increase the risk of acidosis."

Shorter silage lengths mean that straw or hay can be added to the mix to increase chop length as required, adds Mr Clay. "But if the forage is cut long then it is very difficult to alter the TMR total chop length."

Other benefits include being able to fill more grass into the silage trailer, reducing haulage runs, and improved clamp consolidation. However, producers should not be tempted to go for short maize silage cuts to further help with clamp consolidation, he warns.

"On many farms maize is chopped too short - down to 6mm in some cases. In recent years the incidence of displaced abomasums has increased in many herds, and short chopped maize is often associated with this."

Producers should avoid chopping maize below 15mm for all diets, says Mr Clay. To ensure good gut fill, they should offer access to feed throughout the day, and mix rations carefully.

"A well mixed diet will have no lumps of silage or concentrates and forage will not be shredded," he said. "A simple technique to check if the current diet forms an adequate mat on the top of the rumen liquid is to take a sample of the feed and drop it into a clear bucket of water. Much of the material will settle to the bottom but between 15% and 20% should float".

It is also important to manage your silage clamp carefully, he adds. "Fill the clamp level in thin layers, not a steep wedge, and when the pit is full give it a last comprehensive rolling and then seal it tightly to prevent excess air getting in to spoil the fermentation".

However, over rolling the clamp can suck air back in, so producers should be careful of the machinery used. "Pay particular attention to rolling and sealing the edges of the pit as considerable waste can occur here. Given the spiralling costs of feed it is essential to both minimise waste and maximise feed efficiencies."

3:28pm Tuesday 15th July 2008

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