Also known as
Zamia poisoning or the Wamps
This is a fatal nervous disease that can affect cattle if they browse on leaves (particularly the young shoots) or fruit of cycad trees—especially those of the genus Zamia. If an animal eats very much of this plant, the result is irreversible paralysis of the hind legs, due to degeneration of the spinal cord.
The cycad is a group of plants with palm-like leaves arranged in a rosette pattern around a cone at the top of a single trunk. There are at least 10 species of cycads found in the Northern Territories of Australia and extending along the coastal areas of the gulf.
These plants typically have a stout, woody trunk with a crown of large, stiff, evergreen leaves. They usually have pinnate leaves. Cycads vary in size from small (trunks only a few centimeters in diameter) to several meters (9 feet or more) tall. They usually grow very slowly and live a long time, with some specimens known to be at least 1,000 years old. Because of their superficial resemblance to palm trees or ferns, they are sometimes mistaken for these species, but they are not closely related to either group.
Grazing cattle in regions where these plants grow can become costly due to annual losses from poisoning. Zamia (sometimes called zamia palm or burrawong), grows in eastern Queensland and inland to the Central Highlands. The cycad genera in Australia that can poison cattle include Cycas, Macrozamia and Bowenia.
Cattle may graze cycads when other feed is scarce or if young leaves or seeds are available, particularly after bushfires. Poisoning may be progressive over a number of years; cattle that have grazed cycad-infested country may show signs even after being imported to cycad-free county. The syndrome is seen in cattle and rarely in sheep. Water buffalo are also reportedly susceptible.
Zamia staggers may appear after just 14 days of eating the plant, but signs are usually slowly progressive over a number of years.
Initial signs include frequent dribbling of urine, holding the tail to one side, and walking sideways due to the tendency of the hindquarters to fall to one side. The hind legs may over extend or over-flex. In the early stages, over-extension creates a high goose-stepping gait and in later stages there is too much flexion of the fetlocks and the animal is walking on the front parts of the foot.
The gait worsens if the animal has to move very much. After eating the leaves for some time (generally more than 14 days), the animal loses coordination of the hindquarters, staggers about and eventually falls, or drags itself along on the forelegs with the hind legs trailing behind.
Whenever the animal falls, it crashes heavily to the ground, with a “wamp” in farmers’ terms, which led to calling this disease “the wamps” in some regions.
Cattle that develop neurological signs and are subsequently removed from the zamia do not recover. They may improve a little if removed from the source of poisoning, but recovery is never complete; they remain in that condition for the rest of their lives. Some die through misadventure when falling down banks and into gullies. Severely affected animals may not be able to reach food or water
The unstable condition of affected cattle makes them difficult to market, as they are likely to fall down in transit and cause other animals to go down and become injured. As the condition is nervous, the quality of the meat is not affected.
- Goose-stepping gait in the hind limbs
- Knuckling of the hind fetlock
- Wasting of the hindquarters
Cycad leaves and seeds contain at least two toxins. One is a chemical that damages the liver and intestines, and the other is a neurotoxin causing irreversible damage to the nerves of the spinal cord. All mammals can be poisoned, but cattle seem to be most affected by the neurotoxin—though it generally takes a large consumption to poison cattle. The neurotoxin responsible for this condition has not yet been identified but these plants also contain a chemical known as MAM, which can be damaging to the liver.
The seeds and young fronds appear to be quite palatable and are readily eaten, especially when other feed is scarce. This can occur commonly with regrowth after bushfires. These are also the most toxic parts of the plant. The seeds contain a toxic alkaloid (macrozamin) which can cause gastroenteritis and jaundice in sheep. The seeds of a South African cycad also contain macrozamin.
The paralysis and incoordination of the hindquarters is the result of degeneration of nerve fibers in the spinal cord. Additionally, signs of liver or alimentary tract damage, such as jaundice and diarrhea, due to the MAM toxins may be seen in cattle showing zamia staggers.
Experimental research from the 1890s through the late 1900s showed the effects of the toxins; feeding calves on young leaves at a rate of 4 pounds daily for 11 days or 6 pounds daily for 7 days reproduced the disease in experimental animals.
These studies reported that the first signs of the paralytic condition appear after about 14 days of zamia feeding, when 2 to 4 pounds of any part of the plant are consumed daily.
The only good way to prevent poisoning is to keep cattle from having access to these plants, especially those with fruit or young fronds. Removal of these plants from a grazing area may be illegal, however, since many cycad species in Australia are threatened. A permit may be required to remove or poison them. If removal or exclusion fencing is not possible, the stockman must provide adequate feed supplement for the cattle, to help reduce intake of cycads.
One control method that often works is to fence off the zamia country and only graze it for short periods when feed in that area is plentiful (and/or supplementary feed available), and when the young shoots and seeds are not evident.
Chemical control of cycads (where permitted) is difficult. Growth of new young shoots from the base of the plant will occur if chemical treatment is not thorough enough. The use of Tordon 75D injected into the stem is effective and is registered for this use, but chemical control of zamia is usually not economical because it grows in areas that generally don’t have a lot of good forage for livestock.
There is no treatment for zamia staggers.