* STOXX 600 down 0.1 pct
* Bayer strikes deal to buy Monsanto
* Energy stocks suffer from oil slump
* Ocado and luxury stocks fall
* DKSH gains after upgrade (ADVISORY- Follow European and UK stock markets in real time on the Reuters Live Markets blog on Eikon - see cpurl://apps.cp./cms/?pageId=livemarkets)
By Alistair Smout and Kit Rees
LONDON, Sept 14 (Reuters) - European shares ended slightly lower on Wednesday, giving up earlier gains as oil and luxury stocks declined, with Bayer closing off its highs after clinching a $66 billion deal to buy Monsanto.
German drug and chemical company Bayer finished with a gain of only 0.3 percent, having been up as much as 4.7 percent after news of the deal broke.
The $128-a-share deal was cheaper than many analysts expected, with some saying that it would help Bayer to maintain its competitive position.
However, Bayer's pursuit of Monsanto has been criticised by shareholders and the deal faces substantial regulatory hurdles. Some analysts also said that the final deal's substantial equity component took the shine off the good price.
"We think this increased equity component may disappoint investors, but short-term some relief is likely to be found in the lower than expected price," Baader Helvea analysts said in a note.
"That said, we now see the real work beginning as to getting the deal approved by the relevant authorities, leaving uncertainty about how the final combined entity will look. As such, we expect the shares to trade sideways near term."
The STOXX 600 closed 0.1 percent down, ending in slightly negative territory as a sell-off in oil prices intensified, knocking the heavyweight energy sector.
It was a fifth day of losses for European shares, extending recent weakness after markets sold off globally on concern over the effectiveness of central bank policy.
Equities have been under pressure after the European Central Bank said last week that an extension of its stimulus programme had not been discussed and amid speculation about a potential interest rate rise from the U.S. Federal Reserve next week.
Mark Dampier, head of research at Hargreaves Lansdown, said he expects markets to be nervous ahead of key meetings from the Fed and the Bank of Japan this month.
"My view on the market is that it's going to be pretty flat, possibly down, over the next few days while they wait for yet another ... macro-statistical event to come out," he said.
Luxury stocks lost ground, with France's Hermes falling 8.8 percent after saying that it would no longer provide an annual sales growth forecast, starting next year, because of an uncertain trading environment.
Swiss watchmaker Richemont fell 3.9 percent after it reported a 13 percent sales decline in the five months to August, with shares in Swatch Group also dragged lower.
Britain's Ocado extended losses from the previous session, dropping 7.6 percent after BNP Paribas cut its rating on the stock to "underperform". Ocado fell on Tuesday after warning on margin pressure in its third-quarter update.
Swiss business support services company DKSH was a leading gainer, up 4.9 percent on the back of an upgrade from Credit Suisse to "outperform". (Editing by David Goodman)