Solution to summer staggers risk from cathead

Dr Chris Bourke is monitoring these Border Leicester ewes to find a solution to Tribulus staggers at NSW Department of Primary Industries’ Orange Agricultural Institute.
Dr Chris Bourke is monitoring these Border Leicester ewes to find a solution to Tribulus staggers at NSW Department of Primary Industries’ Orange Agricultural Institute.

Research is underway to give central-western graziers a remedy for a crippling and fatal disease of sheep - Tribulus staggers.

First identified in 1937 as Coonabarabran staggers, the disease is caused when sheep eat cathead plants (Tribulus terrestris) growing on bare cultivation following a drought.

NSW Department of Primary Industries principal research scientist, Chris Bourke, has studied the disease for close to 25 years and said that current conditions could see its return this season.

“With summer rain we can expect to see cathead growing from January until May and because it may be the only green plant around sheep will naturally be attracted to it,” Dr Bourke said.

Dr Bourke is currently investigating secondary causes of the disease which graziers may be able to control to reduce the occurrence of fatalities in their flocks.

“It may be a mineral adjustment to feed which will protect sheep from the toxic effects of cathead,” he said.

“We’ve learned a lot about the weed and the toxins it produces since the 1982 drought when large numbers of sheep, up to 50 per cent of some Border Leicester studs, in cathead-prone areas were affected.”

The weed grows when summer storms deflect off the Warrumbungle Ranges and bring rain to farms along the Castlereagh River from Binnaway to Mendooran.

It has continued to trouble graziers following major droughts in an area bounded by Dubbo, Coonamble, Coonabarabran and Dunedoo with reports also coming from Mudgee, Wellington, Cumnock, Gulgong and Molong.

Toxins in the weed cause sheep to go weak in the hind legs and has had a marked effect on British and cross-bred sheep because they tend to eat more cathead than Merinos according to Dr Bourke’s research.

“Cattle can be used to graze paddocks with a heavy cathead cover and Merinos should be grazed on cathead ahead of British breeds.

“Signs of the disease may not show up until several months after animals have grazed on cathead but once the symptoms are detected it’s too late to save the sheep.

“Hind leg weakness is always more pronounced on one side which causes the animal to lean to one side and move diagonally with a distinctive stagger, rather than straight ahead.”

Graziers can contact their local Rural Lands Protection Board district veterinarian.