Executives at American network Fox have been threatened with a $25,000 (£16,666) fine for failing to respond to a U.S. TV regulator's enquiry into 100,000 complaints over an episode of American Dad.America's media watchdog, the Federal Communications Commission (FCC), was flooded with grievances from angry viewers who were offended by an episode of Seth MacFarlane 's animated comedy in January, which depicted a horse ejaculating.FCC chiefs claim Fox bosses have repeatedly failed to respond to an enquiry into the programme, and have threatened the station with a huge penalty.However, a spokesperson for the network insists executives are baffled by the action due to "the fact that we responded to all of the questions related to the substance" of the investigation.The network has now vowed to "respond in greater detail to the Commission in due course".