Poisonous plants
Poisonous plants

Prevent plant poisoning in livestock

Ellanie Smit
A significant number of livestock mortalities on farms can be attributed to plant poisoning.

These incidents occur mostly during the months of spring, at the onset of rainfall activities, or during drought periods, especially in degraded rangelands.

This is according to Erastus Ngaruka, Agribank’s technical advisor for livestock and rangeland.

He says that many rangeland species contain chemicals that are poisonous when eaten.

Poisonous plants vary in their toxicity and the symptoms displayed by affected animals.

Ngaruka says that generally, the level of toxicity can be classified into two groups: plants that are extremely toxic and those with low toxicity levels.

Quick and slow

Extremely toxic plants such as poison leaf only have to be ingested in small amounts to cause harm or for animals to show signs of poisoning. Whereas plants with lower toxicity, such as Geigeria ornativa, show their effects after being consumed in larger amounts and over a longer period.

Ngaruka explains that the toxicity of poisonous plants is influenced by several factors such as soil type, climatic factors, seasons, plant growth stage, which parts were eaten, and plant moisture content, among others.

"Poisonous plants have different effects on animals and different clinical signs; they are classified as plants either causing heart problems, nervousness, diarrhoea, liver damage, obstruction in the gut, skeletal and skin problems, reproduction problems, and those that cause discolouration in meat and milk."

Different stages

Moreover, some valuable forage plants become toxic when overconsumed, eaten at a certain growth stage, or when certain parts, such as flowers, are consumed.

For example, Tribulus terrestris is a common weed in many areas and a valuable forage plant that is well-utilised by livestock when green, but it becomes poisonous when wilting.

Ngaruka says that fodder plants like lucerne, maize and others can also cause nitrate poisoning. For example, when hay is spoiled and mouldy due to poor storage when it gets wet.

"In many rangelands, poisonous plants mostly emerge during spring months and when pastures are in poor condition or overgrazed. In some rangelands, however, they form part of the plant composition throughout the year."

Care must be taken

He says that animals are vulnerable to poisonous plants due to basic factors such as hunger, being unfamiliar with a new area, or accidentally ingesting poisonous plants.

The basic means of preventing and treating plant poisoning is to avoid overgrazing and preventing animals from grazing in areas where poisonous plants tend to grow.

Ngaruka says that in the event of a suspected poisoning, the animal should not be allowed to drink water for at least two days, especially when poisoning is suspected to be from an extremely toxic plant, and the animal should be handled with care and not stressed.

"Farmers should familiarise themselves with their rangeland and develop an inventory of local valuable plants and poisonous plants."


Namibian Sun 2022-12-04

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