S&P 500 Slides Below Closely Watched Threshold

Wall Street ended lower on Monday, falling out of lockstep with oil prices as energy and healthcare shares lost ground.

U.S. indexes gave up early gains despite a 3 percent rally in U.S. oil prices. Stocks and oil have been strongly correlated in recent months as crude prices tanked to decade lows, and their movements in opposite directions during the session was notable to investors.

Following gains last week, technical trading dominated the action as the S&P 500 fell below its 50-day moving average, a sign seen as bad for sentiment. The index broke above the average on Thursday for the first time this year.

"If stocks rally up to a declining 50-day average, people will sell against that," said Michael Matousek, head trader at U.S. Global Investors Inc in San Antonio. "From a psychological standpoint, you have that overhead resistance at that level."

Nine of the 10 major S&P sectors fell, led by a 1.58 percent decline in the healthcare sector .SPXHC, with Amgen Inc (AMGN.O) down 3.60 percent.

The energy index .SPNY fell 1.16 percent despite a 3 percent increase in the price of U.S. oil amid signs that a 20-month selloff could be hitting bottom.

The S&P utilities index .SPLRCU was the lone gainer, up 0.2 percent and helped by a 1.34 percent increase in Edison International (EIX.N).

The Dow Jones industrial average .DJI fell 0.74 percent to 16,516.5 points and the S&P 500 .SPX lost 0.81 percent to 1,932.22.

The Nasdaq Composite .IXIC dropped 0.71 percent to 4,557.95.

For the month, the Dow rose 0.3 percent, the S&P 500 lost 0.4 percent and the Nasdaq lost 1.2 percent.

Strong data, including improving consumer spending, released last week suggested the U.S. economy was recovering better than expected, raising expectations that the Federal Reserve will hike interest rates this year.

After the bell, Workday (WDAY.N) fell 1 percent as the cloud-computing company reported a bigger quarterly net loss, hurt by higher spending on sales, marketing and product development.

Shares of Endo International (ENDP.O) slumped 21 percent after the pharmaceutical company's revenue forecast missed estimates.

Valeant (VRX.N) tumbled 18.41 percent after the Canadian drugmaker said its chief executive would return from medical leave and it delayed the release of its quarterly results.

Icahn Enterprises (IEP.O) rose 3.68 percent after the activist investor offered to buy the rest of Federal Mogul (FDML.O). Shares of the auto parts maker soared 45.78 percent.

Although the main indexes closed lower, advancing issues outnumbered decliners on the NYSE by 1,593 to 1,453. On the Nasdaq, 1,545 issues fell and 1,283 advanced.

The S&P 500 index showed seven new 52-week highs and two new lows, while the Nasdaq recorded 38 new highs and 46 lows.

About 8.0 billion shares changed hands on U.S. exchanges, above the 8.9 billion daily average for the past 20 trading days, according to Thomson Reuters data.