The Oprah Winfrey Network fired its top executive, Christina Norman, after dissatisfaction with the four-month-old channel's ratings, people familiar with the matter said.

The network, which is jointly owned by Oprah Winfrey and Discovery Communications Inc., said Friday that Peter Liguori, Discovery's chief operating officer, is replacing Ms. Norman as CEO on an interim basis, effective immediately. Mr. Liguori will continue to serve as chief operating officer at Discovery while heading OWN.

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