WASHINGTON (Reuters) - The Fox News debate without front-runner Donald Trump attracted the second-smallest audience of the seven such televised encounters among Republicans so far this election cycle, according to ratings figures released on Friday. According to Nielsen data, about 12.5 million people watched the Republican face-off, beating only an earlier debate on the less-prominent Fox Business Network.  But Thursday’s encounter was one of Fox News’s biggest-ever hits and drew more viewers than coverage of a rally at the same time that was hosted by Trump. The billionaire refused to participate in the debate out of anger that Fox News anchor Megyn Kelly was a moderator.  Last-minute phone calls with Fox News Chairman Roger Ailes failed to resolve their dispute, which broke out just days before next week’s Iowa caucuses, the first nominating contest for the Nov. 8 presidential election.     Instead, Trump held his own rally in Iowa at the same time as the debate, which he promoted as a way to raise money for charity. CNN and MSNBC gave his event some coverage, but their combined audience during that time was about a quarter of the crowd watching the Fox debate, according to Nielsen data.  On Friday, Trump defended his decision to snub Fox News, one of the most powerful media forces in Republican politics.          “I have a very good relationship with Fox, but when somebody doesn’t treat you properly, you’ve got to be tough,” he said at a rally in New Hampshire. Trump often claims on the campaign trail that he is responsible for strong viewership of Republican debates. And he managed to upstage the debate to a certain extent, dominating Twitter mentions and Google searches during the event.      Despite Trump’s absence, Thursday’s debate was the second-largest audience ever for a Fox News telecast, beaten only by the first Republican presidential debate in 2015 with 24 million viewers.     It was also the most-watched program on TV on Thursday night, Fox News said. “The debate topped all TV Thursday night in total viewers including all broadcast shows,” Fox News said in a statement.  Audiences for all Republican debates in the current presidential election campaign have been higher than in previous years, though viewership tapered after the first two. About 18 million people watched a CNN-hosted Republican debate in December. The Fox Business event this month drew the smallest crowd with 11 million viewers. Democratic debates have gotten lower ratings this election cycle.  (Additional reporting by Lisa Richwine and Alana Wise; Editing by Alistair Bell) SAP is the sponsor of this coverage which is independently produced by the staff of Reuters News Agency.