ZURICH, June 13 (Reuters) - GAM Holding's board has repeated its appeal to shareholders to accept a takeover approach from Britain's Liontrust Asset Management the Swiss asset manager said on Tuesday.

Liontrust has published its prospectus for the takeover, with an offer period expected to run from June 28 to July 25, GAM said.

The current GAM board and group management board has agreed to tender its shares in the offer, it added.

"The board believes that the offer from Liontrust is in the best interests of all stakeholders and will create the stability needed to continue to deliver for clients," GAM chairman David Jacob said in a statement.

"Our portfolio managers have indicated their strong support for the offer, and we have had positive feedback from many clients."

The end results of the offer are currently expected to be published in August and completion of the transaction is expected to happen during the fourth quarter of 2023, GAM said.

Liontrust conditionally agreed to acquire GAM Holding AG in a deal that values the Swiss asset manager at 107 million francs, the companies said in May.

But a group of investors led by French billionaire Xavier Niel and Swiss entrepreneur Marco Garzetti, have opposed the all-share offer, saying they want to try to turn GAM around.

Their group, which controls 9.2% of GAM shares last week requested an extraordinary shareholders meeting to replace GAM's board.

GAM said on Tuesday the request "does not constitute a competing offer."

Also on Tuesday GAM announced that Sally Orton, its chief financial officer since August 2022, has resigned and will be replaced by former CFO Richard McNamara.

(Reporting by John Revill, Editing by Louise Heavens)