Graziers warned on photosensitisation risk from grazing winter crops

Local Land Services is warning producers that grazing crops or green pastures brings the risk of photosensitisation in lambs.

Whilst green feed in the Central West is few and far between this year, producers in scattered areas have been lucky enough to receive adequate rainfall to allow grazing of winter crops.

Central West Local Land Services’ District Vets have received a number of reports of photosensitisation this season as a result, said District Vet Dr Nik Cronin.

“Earlier in the season in the south, producers were seeing cases on grazing canola, whereas more recently in other areas lambs grazing cereal crops and other pastures have been affected,” Dr Cronin said.

Photosensitisation, or ‘photo’, is where stock become abnormally sensitive to sunlight due to the presence of photodynamic agents in their skin. Animals get sunburnt on the exposed unwoolled parts of the body.

“In lambs, there is variable swelling of affected areas including ears, eyelids, lips and nose,” Dr Cronin said.

“The swollen ears may droop and are often a distinctive feature of the condition.”

Photo can be primary or secondary. In secondary cases, skin sensitivity is a result of liver disease from eating plants such as cathead and panic grasses, and there are often mortalities where liver damage is severe.

Primary photo is caused by the direct ingestion of plants containing photodynamic compounds. The liver is not damaged, and while mortalities are less likely, production losses from the setback can be significant.

“Episodes of primary disease tend to be sporadic, and have been associated with grazing of a range of plant species, including various grasses, cereals and legumes,” Dr Cronin said.

“Stock may become affected within days of grazing the feed of concern, or during prolonged grazing when there is a change in the plants’ growth phase.”

Photosensitisation on grazing brassicas is more likely to occur when the crop is grazed early.

The recently reported cases in the Central West have been primary photo. Management involves removing stock from the problem paddock and providing shelter from the sun.

Mild cases of primary photo should improve in less than a week, although in cases where sunburn has been severe, recovery may be more prolonged.

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