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Slender iceplant poisoning in sheep
By Roy Butler, District Veterinary Officer, Merredin
Replaces Farmnote 66/93
Slender iceplant (Mesembyanthemum nodiflorum) is a prostrate succulent annual plant that favours degraded, heavy and saline soils. It is particularly prevalent in the eastern wheatbelt. Sheep may actively seek it out, possibly attracted by its high salt (sodium) content. It contains oxalic acid and can cause poisoning.
Once the plant is eaten, oxalic acid enters the bloodstream where it combines with dissolved calcium. This reduces available blood calcium levels, which interferes with muscle function and causes paralysis. The insoluble calcium oxalate, formed from the reaction between oxalic acid and dissolved calcium, causes damage to the lining of the rumen and to the kidneys.
In the wheatbelt there are other succulent annual weeds, related to slender iceplant, which are sometimes referred to as "iceplant". These include common iceplant (Mesembryanthemum crystallinum) and Cleretum papulosum (no common name). These plants may contain potentially toxic levels of oxalate, however they have not been proven to cause stock poisoning.
Occurrence of poisoning
Iceplant germinates at the break of the season, and has small white, yellow-centred flowers in spring. After setting seed, from September to November, the plant characteristically changes from green to red before dying. Individual plants can spread to a metre in diameter and aggregations of plants can cover many hectares.
Iceplant gained its common name from the crystals of salt that glisten along its stems during the early stages of growth. Poisoning normally occurs from October to April. This corresponds with the plant being most toxic when it is dead. The plant's toxicity increases after it dies and it remains toxic while dry and after summer rain. Iceplant poisoning has occurred in both pasture and stubble paddocks and usually within 24 hours of sheep being moved into a new paddock. Deaths tend to cease after a few days, perhaps because sheep become more tolerant to oxalic acid, or because their desire for salt has been satisfied and they no longer eat the plant. However, ill-thrift can occur if iceplant remains part of a sheep's diet for extended periods. The plant's toxicity increases after haying off and it remains toxic while dry and after summer rain.
Deaths from iceplant poisoning have not been reported in livestock species other than sheep. However, other species, including goats and horses, are likely to be susceptible. Cattle are least susceptible to oxalate poisoning.
Signs of iceplant poisoning
Affected sheep are unable to stand due to muscle paralysis and are often found lying on their chests. In severely affected animals the head will flop into the flank region.
Characteristically, there is a thick but clear discharge coming from both nostrils. Stomach paralysis can cause gases to accumulate in the stomach, giving the animal a bloated appearance. Sheep suffering iceplant poisoning can show signs for several days before dying. Typical post-mortem signs include enlarged, soft, pale-coloured kidneys.
The prescribed treatment is calcium borogluconate (sold under various brand names) given according to label instructions as an injection under the skin.
Calcium borogluconate is available from stock agents and can be administered by farmers. Successful treatment is most likely if sheep are treated when signs first appear.
Affected sheep must not be allowed to lie flat on their sides, as they will become bloated, unable to breathe adequately, and die.
Iceplant is killed easily by cultivation or some herbicides but it often persists among trees, rocks and along fence lines, so on many farms iceplant poisoning is an ever-present risk. There are some management practices which will reduce the risk for sheep. Giving sheep a loose mix of limestone and salt before and during grazing of risky paddocks may help. It is also important that sheep are not hungry when put into risky paddocks so it is advisable to give them a good feed of hay (not grain) immediately before they have access to iceplant. If sheep graze plants, such as bluebush and most saltbushes, which contain low levels of oxalate, before they have access to iceplant, they can develop some tolerance for oxalate.
Drier seasons favour the plant and it is more likely to be a problem after a dry winter. Sheep deaths appear to be less common when more than 25 mm of rain falls during summer after the plant has dried out, although tests have shown that oxalate levels do not decline significantly following heavy rain.
Table 1. Monthly oxalate concentrations in iceplant expressed as a percentage of dry matter
|dry iceplant - sheep at risk|
|May||4.2||old dry plants leached by rain|
|June||0.3||newly germinated plants|
|green growing plant|
|plant flowering, setting seed and turning red|
|iceplant drying out - sheep at risk|
Cleretum papulosum (no common name) contains oxalate but has not been proven to cause stock poisoning.
Common iceplant (Mesembryanthemum crystallinum) contains oxalate but has not been proven to cause stock poisoning.
Slender iceplant (Mesembryanthemum nodiflorum). Dead, dry plant, showing clove-like seed capsules.
Slender iceplant (Mesembryanthemum nodiflorum). Typical appearance in summer on medium-heavy soils. Dead, dry and potentially toxic.
Page updated: December 2010