NITRATE POISONING
By Dr Mackie Hobson BSc(Agric),BVSc

1. Diseases

Nitrate poisoning is a non-diagnosed but a potential rare poisoning of Angora goats in the Karoo.

Where do the Nitrates come from?

Nitrates can be found in chemicals, fertilizers, grasses, weeds feeds and water. In South Africa contaminated water is the major cause of poisoning.

The plants that may be toxic depending on stage of growth, soil, rainfall and temperature include: Maize, Wheat, Ryegrass, Oats, Sorghum, Rape, and Beetroot.  Plants may accumulate nitrates after fertilizer application (especially if cloudy weather) or damage by drought.

Water can be contaminated by nitrates through fertilizers, effluent from feedlots, sewage or rotting organic matter or fixing of nitrates by root nodules in the soil such as by lucerne.

How does poisoning occur?

Nitrate is relatively non-toxic but its conversion to nitrates by ruminal bacteria make it toxic. Nitrite is absorbed into the bloodstream where it oxidises the iron in haemoglobin and so changes oxyhaemaglobin to methaemaglobin.  Methaemaglobin cannot carry sufficient oxygen leading to tissue hypoxia.

Nitrates/nitrites may also be irritant to the intestinal tract and so cause abdominal pain and diarrhoea.

When does poisoning occur?

Usually hungry animals eating large volumes of nitrate rich feed or consuming contaminated water.

Clinical signs

Signs appear 1-4 hours after ingestion and develop over 5-8 days.

• Rapid, difficult breathing
• Raid weak pulse
• Sometimes abdominal pain and diarrhoea
• Dirty mucous membranes
• Incoordination
• Muscle tremors
• Convulsions
• Abortions, last trimester

Post Mortem

• Blood is dark, chocolate brown
• Congested oedematous lungs
• Haemorrhages in s/c and serosal surfaces

Treatment

I/v with 4% solution of methylene blue t 4mg/kg withRecover in 10-15 minutes

Refetence:

Plant Poisonings and mycotoxicosis of livestock in Southern Africa: Kellerman, Coetzer, Naude, Botha