Preventing livestock loss from plant poisoning

A significant number of livestock mortalities in many farming areas can be attributed to plant poisoning, especially in the spring months, at the onset of rainfall activities, or during drought periods.

Agribank’s technical advisor for livestock and rangeland management, Erastus Ngaruka, said that many rangeland plant species contain chemicals that are poisonous to livestock when consumed.

Poisonous plants vary in their toxicity and the organs they affect.

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

"It is advisable that farmers familiarise themselves with their rangeland and develop an inventory of local valuable plants and poisonous plants."



Factors

He said extremely toxic plants such as Dichapetalum cymosum (poison leaf, gifblaar and otjikurioma) will only have to be ingested in small amounts to cause harm or for animals to show signs of poisoning, which may result in sudden death.

Whereas plants with lower toxicity, such as Geigeria ornativa (vermeerbos), 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, seasons, plant growth stage, plant segments eaten, and plant moisture content, amongst others."

Ngaruka said that different poisonous plants cause varying effects and clinical signs in animals.

These can range from heart problems to nervousness, diarrhoea, liver damage, obstruction in the gut, skeletal and skin problems, reproduction problems, and plants causing a taint in meat and milk.



Vulnerable

Furthermore, some valuable forage plants exhibit toxic effects when over-consumed, eaten at a certain growth stage, or when certain plant components, such as flowers, are eaten.

For example, devil’s thorn, a common weed in many areas, is a valuable forage plant that is well-utilised when green but becomes poisonous at the wilting stage.

Ngaruka said in many rangelands, poisonous plants mostly emerge during the spring months (July to October) and when pastures are in poor condition or overgrazed.

"Animals are vulnerable to poisonous plants due to a combination of factors. One of the contributing factors is hunger, especially during periods of forage scarcity or drought where animals can be tempted to consume these plants as they could be the most available green forage."

He said that factor is inexperienced animals, such as the young or animals introduced in a new grazing area, who are not familiar with or cannot distinguish between the local valuable plants and potentially harmful plants.

A third factor will be accidental poisoning, where these plants can grow in a mix and blend well with grazeable plants, resulting in animals consuming them all together.



The basic means of preventing and treating plant poisoning include:

• Avoiding overgrazing and not allowing animals to graze in areas where poisonous plants dominate. Such areas can be camped off and grazed only when the poisonous plants disappear and valuable plants dominate, especially during the rainy months.

• In the event of suspected poisoning, the animal should not be allowed to drink water for at least two days, especially when the poisoning is suspected to be from an extremely toxic plant. Moreover, the animal should be handled with care and not stressed. These are ways to limit or slow down the circulation of poison through the entire body.

• There are remedies that are used to neutralise the poison in the animal’s body, which include hypo and charcoal.