* Union, Deka, DWS say top management should stay on for now
* Analyst says AGM vote invites activist investors
* Bayer in bid to reassure staff over media coverage (Adds DWS, Bayer staff letter, analyst quote)
By Ludwig Burger
FRANKFURT, April 29 (Reuters) - Three of Bayer's largest German investors said the drugmaker's embattled management needed to stay at the helm to avoid further upheaval, despite their unease over a share price slump in the wake of the $63 billion Monsanto takeover.
The backing for Chief Executive Werner Baumann comes after an unprecedented rebuke at the annual shareholder meeting on Friday, where a majority of investors cast a vote of disapproval of top management's actions.
"A hasty replacement of the CEO would only increase the risk of a break-up and therefore can't be in the interest of long-term oriented investors such as Union Investment," said Janne Werning, an analyst at Germany's Union Investment which is a top-20 shareholder.
"The scale of the litigation risks won't become clearer before next year, that's why we think it's fair and necessary to grant top management more time," he said in a written statement over the weekend.
DWS, the asset management arm of Deutsche Bank, said on Monday it currently also saw no merits in ousting Bayer's top managers.
Union had been among top-20 investors who cast a 'No' vote in Bayer's annual AGM poll to ratify management's business conduct during the year under review, saying the legal risks associated with Monsanto had been known for many years.
About 30 billion euros ($33 billion) have been wiped off Bayer's market value since August, when a U.S. jury found it liable because Monsanto had not warned of alleged cancer risks linked to its weedkiller Roundup. More than 13,000 plaintiffs are claiming damages.
Bayer shares were 2.3 percent lower by 0910 GMT on Monday, as the stock traded without the right to a 2.80 euro per-share dividend for the first time.
Bayer is appealing or plans to appeal the Roundup verdicts and has pointed to global regulators' findings that the use of glyphosate, the active ingredient in the herbicide, is safe.
Ingo Speich, a fund manager at Deka Investment, said on Friday that management change would only compound the chaos.
"It can't be in anyone's interest to see the daily operations being neglected, on top of all the existing chaos," he said at the AGM.
In a cautionary reminder of the risks of management turmoil, shares in German engineering group Thyssenkrupp continued to slide after both the CEO and chairman quit last year amid calls from activist investors to change strategy.
Markus Mayer, an analyst at brokerage Baader Helvea stressed the potential benefits of a management shake-up.
"Activist investors or strategic buyers ...might replace the supervisory board and management and split up and/or take over parts of Bayer. As we see significant valuation upside for Bayer," he said on Monday.
Over the weekend, Bayer's management was at pains to reassure staff over any fallout from the AGM vote, saying it was the backing from the non-executive board that counted.
"The stockholder vote will generate press attention and speculation about Bayer's leadership. You will likely read about it in the media or face questions from friends and family," Bayer's executive board told employees in a letter seen by Reuters.
It said the vote had no legal consequences.
"The Supervisory Board's vote of confidence in us as the Board of Management gives us a clear mandate to lead our company," managers went on to say.
Bayer's non-executive supervisory board won 66.4 percent of the votes ratifying its business conduct at the AGM. Though a majority, the result came in far below a nod of 95 percent or more that is the norm at German AGMs. ($1 = 0.8961 euros) (Additional reporting by Patricia Weiss Editing by Keith Weir)