The basics of plant poisoning

ELLANIE SMIT

WINDHOEK

Farmers are advised to familiarise themselves with their rangeland, develop an inventory of local valuable plants and poisonous plants.

A significant number of livestock deaths in many farming areas can be attributed to plant poisoning.

Agribank’s technical advisor for livestock and rangeland, Erastus Ngaruka, says many farmers have reported poisoning symptoms, especially during the spring months of July to October, at the onset of rainfall activities or during periods of drought, particularly in degraded rangelands.

According to him many rangeland plant species contain chemicals that are poisonous to livestock 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 as plants that are extremely toxic and those with low toxicity levels.

The extremely toxic plants such as poison leaf, commonly known as gifblaar in Afrikaans, only have to be ingested in small amounts to cause harm or for animals to show signs of poisoning.

Plants with lower toxicity, such as common geigeria, show their effects after being consumed in larger amounts and over a longer period.

“The toxicity of poisonous plants is influenced by several factors such as soil type, climatic factors, season, plant growth stage, plant part eaten and plant moisture content,” says Ngaruka.

Symptoms

He says 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 plants causing a taint in meat and milk.”

He adds that there are also some valuable fodder plants with toxic effects when overconsumed. For example, devil’s thorn, which is a common weed, is a valuable forage plant that is well utilised when green, but becomes poisonous when wilted.

Others include grasses such as quick grass and guinea grass.

Fodder plants like lucerne, maize and others can also cause nitrate poisoning, for example when hay is spoiled and mouldy.

“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.”

Prevention and cure

He explains that animals are vulnerable to poisonous plants due to hunger, not being familiar with the local forage or ingesting it by accident.

The basic means of preventing and treating plant poisoning include avoiding overgrazing and not allowing animals to graze 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 be stressed.

Additionally, there are remedies that are used to neutralise the poison in the animal’s body, such as Hypo and charcoal. These remedies and others are readily available in agriculture shops and their application should follow the instructions on the labels.

There are guidebooks for more information and to assist with the identification of these plants. Such books include ‘Toxic Plants of Veterinary Importance in Namibia’ and ‘Grasses of Namibia’.