A research project conducted by the Western Port Catchment Landcare Network has proven the point by monitoring the effects of temperatures on livestock in unsheltered areas compared with areas protected by Landcare-funded shelter belts.

"The results have been startling," said the network's beef and dairy project officer, Peter Ronalds, who confirmed similar research done interstate.

Mr Ronalds said when the cold change came through on Christmas Day last year, the temperature in the shaded area was 20 degrees.

In contrast, the temperature in the unsheltered area was 13 degrees.

"Dairy cattle with shelter produce 17 per cent more milk compared to cattle with no shelter," he said.

The results on hot days were just as stunning. Mr Ronalds said it was 32 degrees in the shade on January 10, whereas the temperature was 40 degrees in the sun.

"On a 27 degree day, unsheltered cows will have 26 per cent less milk than shaded stock," he said.

The research quantified what farmers have also suspected, giving a boost to agricultural productivity, which has risen by 3.8 per cent annually over the past decade.

Source: The Age