Many rangeland plants contain chemicals that are poisonous to livestock when eaten. Poisonous plants vary in their toxicity and the symptoms displayed by affected animals. Generally, the level of toxicity can be classified into two; the first consist of extremely toxic plants and those with low toxicity. The extremely toxic plants such as Dichapetalum cymosum (Poison leaf/Gifblaar) will only have to be ingested in small amounts for animals to show signs of poisoning whereas the low toxic plants such as Geigeria ornativa (Vermeerbos) show their effects when eaten in larger amounts and over a longer period.
Poisonous plants mostly emerge during spring months (e.g. August/September/October) and when pastures are in poor condition or overgrazed. Animals are vulnerable to poisonous plants due to the following basic factors amongst others:
– Hunger; animals are supposed to satisfy their daily forage requirements, thus, if the valuable forage is depleted, then the animal will be tempted to eat any available plant to satisfy their daily need and in the process also eat poisonous plants. This is more likely to occur during drought periods and when the rangeland is degraded.
– Inexperience; this can be attributed to animals being new in the area or young and thus they are not familiar with the local forages or cannot distinguish the valuable plants from the poisonous plants. It is thus advisable to avoid introducing animals to a strange area during the time/season the poisonous plants are active.
– Accident; an animal familiar with the local forage is also vulnerable to plant poisoning as it may ingest it by accident. This is when a poisonous plant has grown close to or blends in with a valuable plant and ingested together. Also, it may be that a poisonous plant may have been harvested together with grass hay.
The toxicity of poisonous plants is influenced by several factors such as soil type, climatic factors, season, plant growth stage, the plant part is eaten, and plant moisture content amongst others. Poisonous plants have a different effect in animals and also 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.
The basic means of preventing and treating plant poisoning are:
– Avoid overgrazing and do not allow animals to graze in areas where the poisonous plants grow.
Such areas can be camped-off and grazed only when the poisonous plants disappear and the other valuable plants dominate.
– In an event of suspected poisoning, the animal should not be allowed to drink water for at least 2 days especially when poisoning is suspected to be from an extremely toxic plant (e.g. Poison leaf), and the animal should be handled with care and not stressed. These are ways to limit or slow the circulation of poison through the entire body.
– There are remedies that are used to neutralize the poison in the animal’s body. These include:
1.Hypo; it is a crystal-like content that should be mixed with water. It can be added to the water in the drinking trough and all animals can drink as they arrive from the veld.
2.Charcoal; this can either be activated charcoal sold commercially or the normal charcoal from the fire. The normal charcoal is the easiest home-based remedy to use. It should be well grinded into a fine content and mixed with water and given orally to the poisoned animal. These remedies and others are readily available in the agriculture shops and their application should follow the instructions on the labels.
3. Finally, it is advisable that farmers familiarize themselves with their rangeland, develop an inventory of the local valuable plants and the poisonous plants. There are guide books for more information, especially with the identification of these plants. Such books include; “Toxic Plants of Veterinary Importance in Namibia” and “Grasses of Namibia” amongst others.
* This article was compiled by Erastus Ngaruka, Technical Officer: Livestock within Agribank’s Agri Advisory Services Division.