Oprah Winfrey and Discovery Communications CEO David Zaslav have run out of excuses: With their unofficial relaunch today of OWN, they’ll have no one to blame but themselves if their struggling joint venture fails to show a big improvement in the ratings following a dismal 3Q. In its targeted demo, women 25-54, OWN delivered a rating of .16 — down 16% vs. the same period last year when the channel was still Discovery Health. OWN may have set a deceptively low bar for itself; word is that it cut back on marketing in preparation for the relaunch. Still, the channel is betting everything on Oprah’s star power — and, to a lesser extent, Rosie O’Donnell’s — and that will be put to the test beginning today with the launch of The Rosie Show (7-8 PM) and Oprah’s Lifeclass (8-9 PM). Winfrey’s program, built on clips from her syndicated talk show, begins with one of her classics: for an episode about “ego,” she will include scenes from the show where she illustrated how much weight she lost from a liquid protein diet by wheeling in a wagon filled with 70 pounds of fat.