Factsheets - Sheep & Beef
The following fact sheets have been prepared by Anexa FVC Veterinarians as a guide to topics of interest. For specific information please contact your local vet.

Nitrate Poisoning in cattle

Nitrate Poisoning in cattle
Nitrate poisoning in cattle occurs when certain plant species accumulate nitrate. The rumen microflora normally convert nitrate to nitrite and then to ammonia, but when intake is too great, nitrite turns blood haemoglobin into methaemoglobin, which cannot transport oxygen. This results in insufficient Oxygen being transported around the body which can result in death.

Sources of Nitrate

Ground water can accumulate high levels of nitrate by leaching from effluent or heavily fertilised soils, but the main source of poisoning in cattle is usually plants.

Why does nitrate accumulate?

Plants take up nitrate from the soil and by photosynthesis convert it to protein for growth. However, if the energy supply is insufficient, then nitrate accumulates to abnormal levels. A deficiency in plant energy supply can be caused by a number of factors:
  • Low sunlight levels
  • Plant stress such as insect damage, frost, freezing, and herbicide use.
  • Stunting and wilting associated with drought.
  • Over application of inorganic nitrogenous fertiliser or excess application of effluent, toxic levels peak 10-14 days after fertiliser application.

Which plants can be affected?

Many plants are prone to nitrate accumulation and many of our commonly used forage and fodder crops are amongst them; Ryegrass, sorghums, cereals, and brassicas. Nitrate concentrations are highest in young plants and regrowth, and are highest in pre-bloom plants, in parts closest to the ground.

Animal factors affecting susceptibility

A single intake of nitrate over a short period is more toxic than accumulating the same amount over several days or weeks.
Allowing hungry cattle access to nitrate will increase risk of poisoning.
Tolerance may be built up in cattle receiving sub-lethal amounts over a prolonged period.
Carbohydrate rich diets help to protect against the effects.

Signs of Nitrate poisoning

The lack of Oxygen to tissues causes the dramatic signs associated with nitrate poisoning. Death can occur within one hour or up to a day after acute poisoning. Animals will show open mouth breathing, abdominal pain, diarrhoea, salivation, collapse and convulsions. The mucous membranes are often brown and there is brown discolouration of the blood.

Treatment and prevention

Animals need to be moved slowly and carefully away from affected paddocks and fed on a high carbohydrate diet such as good quality hay. Affected animals can be treated with intravenous Methylene Blue which converts the methaemoglobin back to haemoglobin and restores the Oxygen carrying capacity of the blood. This is a veterinary emergency and your local Anexa FVC clinic should be contacted immediately if you suspect nitrate poisoning.

Forage can be tested at the Vet clinic to check whether it is safe to feed. High nitrate paddocks can be ensiled, as this reduces the nitrate content of forage, as does allowing plants to age and set seed. In contrast, drying plant material as hay preserves the toxicity.
If high risk pasture must be fed, ensure animals are already ‘full’ and restrict access to one hour at a time, feed other high energy feeds with the pasture and check animals very regularly.

Date Added: Tuesday, 3rd October 2017