Barclays analyst Kannan Venkateshwar says Discovery at a conference yesterday walked back its Q4 U.S. advertising growth guidance due to weaker ratings. The guidance was reduced to 2%-3% growth from 3%-5%. Discovery is now the most ad-exposed name in U.S. media, deriving 60% of U.S. revenues from advertising, and given broader secular challenges across the sector, the impact on multiples is understandable, Venkateshwar tells investors in a research note after the stock dropped 8% yesterday to $28.20. While the company expects the weakness in advertising to be offset by a slightly better pace of affiliate fee growth, the overall pace of U.S. sales growth in Q4 will be 1.3%, among the lowest in the industry, adds the analyst. He keeps an Equal Weight rating on Discovery shares.