13 August 1999

Ragwort in silage can kill…

RAGWORT can kill cattle, not just horses, and is at its most dangerous in silage and hay.

In a letter to Vet Record, Aug 7, West Midlands vet Steve Borsberry warns of the dangers of feeding grass silage contaminated with ragwort.

On one farm attended by Mr Borsberry, 18 cattle have been destroyed due to liver failure resulting from ragwort poisoning from silage.

Bitter taste

"In a grazing situation, cattle dont eat ragwort because it has a bitter taste. But in silage it is less obnoxious so they eat it." Even though the plant is killed during ensiling, it is still poisonous, he warns.

Because there is more ragwort about during July and August, second or third cut silage is more likely to be contaminated than first cut. However, buying in silage of unknown origin also poses a risk, he cautions.

"With producers now buffer feeding all-year round, some buy silage as round bales or in pits. They may have no idea what is in silage. Poisoning is not instant: It takes three or four months before animals start to lose condition and scour.

Silage source

"Be certain of the silage source. If you dont know, get rid of it completely. You should be able to identify ragwort in round bale hay or silage but it is much more difficult with precision chopped silage."

Where fields are infested with ragwort, a combined programme of spraying and hand-pulling is the only way to eradicate it, believes Norfolk based agronomist Peter Kane.

"The first line of action is spraying. This will kill about 90% of ragwort plants, but it isnt totally effective, so the rest should be hand pulled."

Despite being classed as a biennial weed, Mr Kane says it seems to behave more like a perennial and best spraying results would be achieved by treating it as such.

Spray in autumn and then again in spring using 2,4-D at a rate of 2.8-3.5 litres/ha. "Keep livestock away from ragwort for at least a month after spraying – after spraying it loses its smell and taste, meaning stock are more likely to eat it."

But Mr Kane advises producers pulling ragwort to wear gloves. "The alkaloid given off by ragwort can penetrate skin, so its safer to wear gloves."