Watch out for those poisonous plants

One of the greatest risks to farmers is the loss of livestock as a result of plant poisoning. So it’s important to know what promotes
their growth and how to avoid them.

Young animals are more vulnerable to the effects of poisonous plants. Their livers do not have the capacity to eliminate the toxins and they have not yet learnt to avoid these plants.
Photo: Wayne Southwood

About 600 indigenous poisonous plant species are found in South Africa, and different parts of these plants – the leaves, pods or seeds – may be toxic. Losses due to plant poisoning can be direct, causing instant death, for example, or indirect, leading to loss of condition, poor production, such as loss of milk yield, or reproductive failure, such as abortions, birth defects or failure to become pregnant.

Further economic losses include the cost of control and treatment measures, such as fencing, strategic grazing practices, supplementary feeding, veterinary expenses, or diminished land value. Eating meat from animals that have died from plant poisoning can also lead to severe sickness or even prove fatal. Animals usually know to avoid poisonous plants. But if there’s a shortage of food – due to drought, veld fires or overstocking – starving livestock will have no choice but to eat what’s available.


Table 1: The most important plant poisonings in South Africa
CATTLE
GOATS & SHEEP
Cardiac glycosides (for example, tulp and slangkop)
Seneciosis
Gifblaar
Gousiekte
Lantana
Diplodiosis
Geeldikkop
Vermeersiekte
Cardiac glycosides (for example, tulp and slangkop)
Seneciosis
Gousiekte
Diplodiosis

SOURCE: ARC-Onderstepoort Veterinary Institute

Factors contributing to the likelihood of plant poisoning include:

  • After the dry season or a veld fire, poisonous plants are usually among the first green plants to appear. A number are also at their most toxic in the young stage when they’re most attractive to stock.
  • Some poisonous plants are highly resistant to drought and may be the only green plants available for animals to eat.
  • Poisonous plants are often found as weeds in harvested lands and along roads – areas used for grazing in times of scarcity.
  • Wind or hail can knock acorns or pods from poisonous plants to the ground, making them available to animals.
  • Fertilisers may increase the toxicity of some plants.
  • Animals are sometimes poisoned when feeding on fodder such as hay, silage, stover or concentrates containing poisonous plants, fungi or chemicals.
  • Young and older animals are more susceptible. Their livers do not have the capacity to eliminate the toxins.
  • Hungry animals graze more greedily and are less selective and therefore more likely to be poisoned. As noted, this can occur in conditions of drought, veld fires or overgrazing. Pregnant animals also tend to be less selective and have a higher intake than normal and may therefore be poisoned.
  • Thirsty animals look for plants with a high moisture content which they would normally avoid. Some of these plants may be poisonous.

Symptoms
The various poisonous plants contain many types of toxins that affect the body in different ways. For example, some might affect organs such as the heart, while others might affect the liver. In some cases, a single toxin will target more than one organ. Some signs of poisoning are listed in Table 2. Unfortunately, many of these resemble those of other diseases, so it’s a good idea to know which poisonous plants are found in your area.

Table 2: Signs of poisoning
URINARY SIGNS: Little or no urine production, swelling of the belly, change in colour of the urine, which may also contain crystals (small stones), a great thirst. In dead animals: crystals in the kidney, swollen, wet kidneys filled with fluid. DIGESTIVE SIGNS: Animal stops eating, salivation, dehydration, fluid from the mouth and nose, vomiting, constipation, diarrhoea, swollen belly. In dead animals: large quantities of fluid may be seen in the gut, as well as changes in colour and smell of the gut contents.
NERVOUS SIGNS: Restlessness, sensitivity to sounds and touch, high-stepping, difficulty in walking, muscle tremors, aimless wandering, staggering, blindness, convulsions, paralysis. REPRODUCTIVE SIGNS: Difficulty giving birth, poorly developed udder, enlarged belly, enlarged vulva, suppressed milk production, abortions, deformed young, males not interested in mating.
HEART SIGNS: When the heart is affected, an animal may drop dead suddenly when it is being chased, for example. Also, the animal tends to stand with its head low and the stomach tucked in. It sometimes grinds its teeth or groans, and the heart rate increases. Bloat, diarrhoea and weakness of the hind legs can also occur. BLOOD/BLOOD-COMPONENT SIGNS: Pale, yellow, bluish or brownish membranes, green-tinged faeces, listlessness, animal stops eating, will bleed easily, red-wine to coffee-coloured urine. In dead animals: ulcers in the stomach, bleeding, and a pale yellow, blue or brown colouring of the carcass.
RESPIRATORY SIGNS: Increased breathing rate, animal grunts when breathing, frothing at the mouth. In dead animals: fluid and gas in the lungs, signs of infection in the lungs (pneumonia), froth in the windpipe. SKIN SIGNS: Itchiness and reddening of skin, scale or crust formation, rough coat, thick fluid on the skin, hair or wool loss, animals seek shade, feet are warm and painful to the touch, difficulty in walking.
SIGNS OF BONES & TEETH: Uneven, mottled or black teeth, animal shifts weight from one leg to the other, stiffness, bones fracture easily. LIVER SIGNS: Vomiting, yellow discoloration of membranes, swelling of the belly and face. In dead animals: fluid in the chest and abdomen.

If an animal gets sick or dies, inform your animal health technician or state vet. They will examine dead animals and send samples to a laboratory for testing, as well as searching for poisonous plants where the animal grazed. Once you know what type of poisoning has occurred, you can decide on the best treatment and prevention. In many cases, there is no treatment.

But if you know which type of plant is involved, you will know whether treatment, such as feeding the animal activated charcoal to ‘soak up’ the poison, will help. Although many animals recover with or without treatment, a number of plant toxins affect them for the rest of their lives, reducing growth and productivity of stock as well as their resistance to other diseases.

Prevention

  • Know which poisonous plants occur in your area, and keep your livestock away from them.
  • Keep animals in good condition with supplementary food and licks during the dry season – and always make sure they have enough water.
  • Take care when introducing animals from other areas (especially exotic breeds); they may be unaccustomed to the plants on your land.
  • It may be necessary to eradicate some of the poisonous plants.
  • Don’t feed your animals mouldy hay or hay cut from areas where poisonous plants occur.

Source: Animal Health for Developing Farmers Programme, ARC-Onderstepoort Veterinary Institute. Call 021 529 9158 for more information.