Silage loaded on a truckWashing tyres before they enter the clamp can help reduce soil contamination in silage. © Tim Scrivener

Farmers must take steps to reduce soil contamination in this year’s silage following a number of fatal listeria cases last winter, one vet practice is warning.

Ben Brearley from the Livestock Partnership in West Sussex says he has seen more than a dozen cases of the disease in suckler cows and ewes at lambing. Three of these have been fatal.

Listeria is a bacteria that lives in the soil and can be ingested by livestock if forages become contaminated with soil. If it is not spotted early enough it can be fatal, but it also causes abortion.

It is particularly problematic in poorly fermented silages where the pH isn’t acidic enough, says Mr Brearley.

Symptoms of listeria

  • Depression and suppressed appetite
  • Circling with a head tilt
  • Unable to stand
  • Animals may propel themselves into fences or hedges

“It is a perennial problem – we tend to see repeated cases every year. If the animal has ulcers in its mouth or new teeth the bacteria can penetrate that nerve and cause brain abscesses.”

See also: Find out how to make good-quality silage by reading our academy

Early treatment is critical, he adds. “Animals will respond well to antibiotics if you get it to them early enough. Treatment isn’t expensive and if done quickly and animals get good care – making sure they have easy access to feed and water and they’re not in an area where they are going to get into mischief – then the prognosis should be quite good.”

Mr Brearley says penicillin and oxytetracycline are both effective treatments, but he advises farmers to consult with their vet to rule out any other cause before treatment.

How to reduce the risk of soil contamination

Dave Davies of Silage Solutions says risk reduction should start in the field during harvest.

“The cutting head should be altered depending on the ground conditions.”

Top tips

  • Pay close attention to sealing the clamp to prevent carbon dioxide from escaping and oxygen seeping in
  • Wrapping bales at the stacking site will reduce the risk of bale damage and spoilage
  • Always check bales have got a minimum of four layers of wrap. If you have had problems in the past, consider more
  • Protect bales from birds using nets
  • Keep the clamp face clean
  • Listeria grows in good silage around mouldy areas, so make sure you remove more than just the mould
  • If you identify a listeria problem stop chopping bales or mixing TMR. This will contaminate the entire ration
  • Get on top of mole problems
  • Rolling grassland after the establishment of a new ley or in the spring before you shut fields up for silage to even out grassland

For new leys and legumes Dr Davies suggests adjusting the cutting height to three to four inches, but two inches is sufficient for permanent pastures.

“If you have a new reseed generally you will need to cut higher because the swards are less dense.”

Dr Davies says grassland heavily contaminated with mole humps should ideally be harvested separately.

“If you must put [contaminated grass] in the clamp, put it in the bottom so it doesn’t contaminate the rest of the silage.

‘If you have got a lot of dead material in the bottom of your sward at cutting then you are going to have a high risk of listeria because it lives on dead material.”

Dr Davies says attention to detail at ensiling is critical.

“Listeria are microaerophilic – they are not anaerobic. They grow with a little bit of oxygen so good compaction and sealing is critical.”

Dr Davies advises the clamp should be rolled in maximum depths of 15cm and must be sealed quickly.

“A small amount of oxygen will keep listeria alive. Many silage clamps have 40% of silage within 1m of the top or side – a significant amount.

“These are the areas that are more vulnerable to oxygen getting in. Once sealed, a silage clamp should blow up. This means carbon dioxide is being released and it will inhibit listeria growth.

“You want quick fermentation to rapidly bring the pH down and prevent listeria from growing.”

Independent grassland consultant Gareth Davies says more emphasis needs to be placed on preventing soil from being carried from the field into the clamp or wrapping area.

“Another big risk factor is carrying mud into the clamp. To avoid this you could set up a temporary wheel wash to clean the mud off tyres before tractors enter the clamp and prevent mud from getting pushed up by the buck rake.”

Mr Davies says the importance of cleaning out clamps before they are refilled should also not be underestimated.

“Make sure the silage pit is clean before you even start putting fresh silage into it.”