Berlin - On the ninth day of their milk boycott, German dairy farmers shifted their demonstrations Wednesday from milk- processing plants to the offices of the grocery chains which they blame for low milk prices.

The farmers have sacrificed more than a week's income in a so far vain battle to force up the milk price in Europe's biggest economy.

Protesters picketed the headquarters of Germany's giant Aldi and Lidl discount supermarket companies, which sell fresh milk at bargain prices, and the head office of Edeka, Germany's biggest grocer.

Grocery trade leaders said they would talk about the price issue with the farmers, but offered no substantial concessions.

The German Cartel Office began an inquiry that may end in a huge fine for the BDM dairy farmers' association. The BDM, which is organizing the fierce protests, is accused of breaking a German law that outlaws economic boycotts.

After legal advice, the BDM had to advise radical farmers on Tuesday to end several days of picketing which had prevented milk supplies from non-striking farms being taken to factories for processing.

Some of Germany's farmers own shares in dairy factory cooperatives and oppose the boycott.

The HDE national retail federation said milk and yoghurt were once again moving out to shops, despite claims by farm leaders that 70 to 80 per cent of milk from Germany's cows was being dumped onto fields or into drains and feed troughs.

Strikers applauded the first and only dairy factory to concede their demand for farm-gate prices to be raised to 43 euro cents (66 dollar cents) per litre. Farmers say they are faced with ruin because current market prices are only two-thirds of that level.

The compliant Berchtesgadener Milk Works said Wednesday it would pay farmers that price though it has no guarantee it will be able to command a higher wholesale price from German supermarket chains.