High nitrate levels kill many sheep

Press, 24 June 1983, Page 11

High nitrate levels kill many sheep

Grazing brassica crops with high nitrate levels has killed more than 100 sheep

in Canterbury in the past few weeks.

Mr Brian Cox, a veterinary investigation officer at the Ministry of Agriculture

and Fisheries’ Lincoln Animal Health Laboratory, said it happened with sheep grazing turnip tops and ®The plants didn’t grow during the drought and nitrogen built up in the soil around the root zone.

"When the rain came the plants couldn’t use all the accumulated nitrogen so stored it in the form of nitrate “This is converted to nitrite in the sheep’s rumen. Nitrite prevents oxygen from getting to the tissues, so the animal dies of oxygen starvation.” Mr Cox said conditions were particularly suitable for the problem this year. The drought had affected plant growth and farmers were probably relying on brassicas earlier than usual because of a shortage of other feed. “There has been a series of cold, cloudy, damp days with not enough sunlight for photosynthesis, and this has also caused problems. “Nitrate levels can vary a great deal over time and in different areas. “Some of the affected: sheep were grazing continuously for about two weeks with no ill effects and then suddenly died, while others had only been grazing for one hour a day for a couple of days,” said Mr Cox. “Farmers can help themselves through good stockmanship, however. “Sheep should be break fed so they can only eat a small amount at a time. If possible they should be given another source of

carbohydrate between break feeds — good quality hay or pasture, for example.

“Don’t leave sheep feeding in a paddock overnight — you could come back in the morning and find half the flock dead.”

To test a field the farmer could put six sheep in for a morning’s grazing and keep an eye on them, Mr Cox said.

“The symptoms to look for are panting, staggering, muscle tremors and general weakness. The mucous membranes around the mouth will be blue through lack of oxygen.” Veterinarians have been advised of the problem and farmers who suspect their sheep may be affected should immediately contact their vet, Mr Cox said.