If you want to finish the hogs, give them all they will eat... pretty much keeping feed in front of them. Mine would pretty much finish what I gave them in 24 hours, but I basically never let them run out of feed.
I am, thinking that whatever breeds are in them.... and I am suspecting some Landrace with the length of body they have. Landrace were popular for colder climates but they had the long floppy ears and long lean bodies. Although, so did some of the large blacks..... the white feet suggest some berkshire in there and they are not as large a hog... so that might be what makes up the base but berks have upright ears....
You are fighting against the cold there and the hogs having to eat to keep up their body heat in the winter.... their feed will go first to maintaining their body heat and condition... so you are going to feed alot more feed in the winter to have them gaining.