Livestock play a vital role in agriculture, but their health can be compromised by ingesting poisonous plants. This is a significant problem in Mzansi, where over 600 indigenous plants pose a threat. By understanding the risks and taking proactive measures, farmers can safeguard their animals and ensure a thriving herd.
Dr Asive Luningo, a clinical assistant toxicologist at the University of Pretoria’s faculty of veterinary science, explores the causes and effects of plant poisoning in livestock, along with crucial prevention and management strategies.
Mzansi’s toxic plants are common
Poisonous plants contain toxic substances that can harm animals when ingested or upon contact. These plants can cause a range of acute and chronic effects, leading to significant direct and indirect consequences.
“About 600 indigenous poisonous plants are known to occur in Southern Africa. The most significant plant poisonings in livestock include those containing cardiac glycosides (such as tulp, slangkoppe, plakkies and milkweed).
“These plants cause acute and chronic syndromes, leading to gastrointestinal disorders, cardiovascular issues, neuromuscular problems, and respiratory distress,” she explains.
Direct effects include reduced milk production, reproductive issues, and even death, while indirect losses involve expenses for control measures, strategic grazing, supplementary feeding, and veterinary services.
“Seneciosis, caused by Senecio species, affects the liver, leading to symptoms like loss of appetite, depression, and icterus. Other harmful plants include Dichapetalum cymosum (gifblaar), Vangueria pygmaea (gousiekte), devil’s thorn, and Geigeria africana (vermeerbos), each causing a variety of severe health issues in livestock,” she says.
Identification and management of toxic plants
Luningo emphasises that proper plant identification is crucial.
“Farmers should recognise plant characteristics such as size, form, leaf shape, flower colour, and odour. Seeking assistance from professionals like botanists, agricultural personnel, animal technicians, extension officers, and veterinarians is essential. Digital photos can be sent to these experts for identification,” she says.
Additionally, joining farmers’ social groups can be beneficial, as members often have experience with these plants. Reliable resources are indispensable for plant identification.
“I recommend books such as Poisonous plants of South Africa by Professor Ben-Erik van Wyk and ‘Plant Poisonings and Mycotoxicoses of Livestock in Southern Africa’ by Professor T.S. Kellerman,” suggests Luningo.
Technological resources and online tools
To the best of Luningo’s knowledge, there is not any app specifically for identifying toxic plants in South Africa.
“However, general plant identification apps exist, although I cannot vouch for their accuracy. Useful online resources include the South African National Botanical Institute (Sanbi), the Global Biodiversity Information Facility South Africa (GBIF), Plants of the World, and iNaturalist,” she suggests.
Symptoms of plant poisoning in livestock
According to Luningo, poisonous plants can affect various organ systems. Symptoms depend on the system affected and the amount ingested. Common symptoms include:
- Tremors
- Ataxia
- Seizures
- Increased heart rate
- Icterus
- Anorexia
- Regurgitation
- Diarrhoea
- Difficulty breathing
- Pale mucous membranes
- Hair loss
Accurate and early diagnosis is crucial for appropriate treatment and the prevention of further cases. Luningo describes the onset and progression of symptoms.
“Symptoms can be acute or chronic. Acute symptoms appear rapidly, often within minutes to hours after ingestion, such as with plants containing cyanogenic glycosides. Chronic symptoms develop slowly over weeks or months. For example, in gousiekte, animals die suddenly 6 to 8 weeks after ingestion,” she explains.
Luningo says that the long-term effects vary.
“They can include the development of cancer, secondary bacterial infections, aspiration pneumonia, teratogenicity, blindness, paralysis, and permanent organ damage,” she explains.
More practical advice for farmers:
- Protect your cattle from three-day stiffness
- Explore artificial insemination in livestock breeding
- Managing foot rot in livestock during breeding season
Prevention strategies
Best practices for preventing livestock from coming into contact with toxic plants include grazing management, feed supplementation during the dry season, and plant eradication.
“Mechanical eradication involves pulling or digging up plants, while chemical methods use herbicides. Biological control, involving living organisms like insects and bacteria, can also be effective. Regular inspection of hay bales and knowing how to identify poisonous species are crucial,” she explains.
Luningo highlights effective grazing management techniques. Helpful techniques include:
- Rotational grazing
- Fencing off infested areas
- Reducing camp size
- Placing less susceptible animals in infested areas
“These methods help prevent overgrazing, reduce exposure, and allow pastures to rest,” she explains.
Effectiveness of physical barriers
Physical barriers are highly effective in restricting access to specific areas. However, they may not be practical in areas with limited grazing space.
“Farmers should contact their local veterinarian immediately if they suspect plant poisoning. Move the animals from the infested area, monitor clinical signs, and provide supportive care as directed by the veterinarian,” she explains.
Regarding treatments, Luningo explains that for most plant toxins, there are limited antidotes.
“Supportive or symptomatic treatment is usually used. Activated charcoal is commonly advised for binding ingested toxins within the gastrointestinal tract,” she explains.
There are guidelines from the department of agriculture on controlling unwanted plants and a list of registered herbicides for weed control.
“Relevant acts include the Fertilisers, Farm Feeds, Agricultural Remedies, and Stock Remedies Act 36 of 1947, the Agriculture Pests Act 36 of 1983, and the National Environmental Management: Biodiversity Act 10 of 2004,” she says.
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