One of the common perennial grasses in pastures and crop stubbles in North East Victoria that would have responded to the recent rains are the panic grasses.
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Panic grasses are also commonly known as fairy grass, witch grass and hairy panic. These grasses can cause photosensitisation and death when ingested, particularly in lambs.
The young, rapidly growing grasses contain steroidal saponins, which when eaten can form crystals in the liver, damaging the liver cells and obstructing the outflow of bile. The breakdown products of chlorophyll, which is found in green grass, are then no longer cleared by the liver and cause damage to skin tissues when exposed to light.
So, the thin skinned, wool-free parts of the sheep which are exposed to sunlight get damaged and show signs like severe sunburn. Typically affected areas are the ears, eyelids, nose, lips and vulva. Affected lambs will seek shade and be reluctant to graze.
The liver damage may lead to jaundice, and with the swelling caused by photosensitisation the condition is sometimes known as "yellow bighead". This liver damage can kill the lambs before photosensitisation develops.
The only treatment is to remove affected stock from the toxic pastures and provide them access to shade.
If this happens promptly, affected stock can recover completely, as the liver has a remarkable ability to heal itself. However, some livers may never recover totally.
The best prevention is to avoid grazing risky paddocks.
