Coming off its least-watched month in primetime in 20 years in May, CNN has taken another big ratings blow: The cable news network has registered to its lowest-rated quarter in primetime since 1991. For this year's second quarter, CNN hit a low among total viewers and the key adults 25-54 demographic, with all primetime programs posting steep declines. The network averaged 446,000 total viewers and 129,000 in the 25-54 demo in primetime. Compared to last year's second quarter, that's down 35% and 41%, respectively. Rival Fox New Channel, meanwhile, with 1.79 million primetime total viewers on average, was down 1% from its 2011 second-quarter numbers. FNC lost 14% in the 25-54, bringing in 355,000 viewers. MSNBC was down 13% in total primetime viewers, with 689,000 on average, and down 17% in the 25-54 with 217,000. The quarter ran March 26-June 22.