Oprah Winfrey struggling to hold her OWN network

Rosie O'Donnell turns 50 today. But the milestone is less merry after Tuesday's final taping of her short-lived talk show on the Oprah Winfrey Network, ending another failed experiment in the channel's tumultuous history and raising new questions about its future.

In another troubling sign, 30 of OWN's 150 staffers were laid off Monday, and Discovery Networks (which co-owns OWN with Winfrey) installed new executives to run its business and programming operations.

Discovery has invested $310 million in OWN, but first-year ratings were merely even with Discovery Health, the channel it replaced. "I've never seen Discovery invest this much money in such a short period," says longtime cable analyst Derek Baine of SNL Kagan.

"The ratings aren't coming in anywhere near as forecast. It would be a huge disappointment for Discovery to have to pull the plug, but it seems like that may be what they're considering at this point, given that they're taking control."

Is that possible? "Absolutely not," says Discovery Networks spokesman David Leavy. "We're in it for the long term."

But the road has been rough. After delays and management shakeups, OWN launched 15 months ago largely without Winfrey, who spent half a year finishing up her syndicated talk show. Her signature series, Oprah's Next Chapter, started only in January, and though it's tops on OWN, ratings are low: Sunday's Lady Gaga interview drew 808,000 viewers, though the interview with Whitney Houston's daughter scored a record 3.5 million March 11.

And OWN, which promised an all-original lineup, has retreated, filling its schedule with repeats such as Deadly Women and Wicked Attraction from sibling Investigation Discovery. Overall ratings are up this year. A network launch "is always a challenge, and ratings grow over time," Winfrey said in a statement Friday.

Not O'Donnell's. The Rosie Show, based in Winfrey's Chicago studio, cost $20 million a year but last week averaged only 130,000 viewers. The finale airs! March 3 0.

With cost-cutting and a new team, "we are poised for some tremendous growth from a business and ratings point of view," says co-president Erik Logan, who will unveil new shows April 5. "We're much more confident that (they're) more on-brand than they were last summer."