Gaga has said to fans in London that Swine is the second single and she likes it more than Applause.
Also Kiss 108 has confirmed it:
Kiss 108 @Kiss108 9h
[MUSIC] @LadyGaGa teases us her second single!!! Listen to part of 'Swine' @KISS108 http://ow.ly/oq6mo
I like what we've heard so far from it but I doubt any of this is reliable, and I don't think she'd announce it this early when “Applause“ is what, only few weeks old. I call ********.